Updated on 2024/04/18

写真a

 
ICHIKAWA, Kohei
 
Affiliation
Faculty of Science and Engineering, Global Center for Science and Engineering
Job title
Associate Professor(non-tenure-track)
Degree
博士 (理学) ( 京都大学 )

Research Experience

  • 2023.09
    -
    2026.08

    Waseda University   Faculty of Science and Engineering   Associate professor

  • 2023.04
    -
    2023.08

    Tohoku University   Frontier Research Institute for Interdisciplinary Sciences/Astronomical Institute   Associate professor

  • 2018.04
    -
    2023.03

    Tohoku University   Frontier research institute/Astronomical Institute   Assistant Professor

  • 2021.03
    -
    2022.03

    Max Planck Institute for extraterrestrial Physics   Visiting Researcher

  • 2020.08
    -
    2020.11

    Parental leave

  • 2016.10
    -
    2018.09

    Columbia University   Department of Astronomy   JSPS fellow/FRIS fellow

  • 2016.04
    -
    2018.03

    National Astronomical Observatory of Japan   Optical and Infrared Division   JSPS fellow (PD)

  • 2015.04
    -
    2016.03

    National Astronomical Observatory of Japan   Hawaii Telescope

▼display all

Education Background

  • 2010.04
    -
    2015.03

    Kyoto University   Department of Astronomy  

  • 2006.04
    -
    2010.03

    Kyoto University   Faculty of Science  

Committee Memberships

  • 2023.08
    -
    Now

    NAOJ/Subaru telescope  Subaru Telescope Time Allocation Committee

  • 2018.04
    -
    Now

    Thirty Meter Telescope  International Science Definition Team (ISDT) core member

  • 2018.04
    -
    Now

    members  TMT ISDT

  • 2019.06
    -
    2023.05

    天文月報 編集委員

  • 2012
     
     

    日本天文学会  評議員

Professional Memberships

  • 2022.08
    -
    Now

    International Astronomical Union (IAU)

  • 2019.01
    -
    Now

    American Astronomical Society

  •  
     
     

    THE ASTRONOMICAL SOCIETY OF JAPAN

Research Areas

  • Astronomy   observational astronomy

Research Interests

  • supermassive black holes

Awards

  • 若手アンサンブルワークショップ講演賞

    2022.11   東北大学  

  • 21st Intelligent Cosmos Young Researcher Award

    2022.05  

    Winner: Kohei Ichikawa

  • 令和4年度 科学技術分野の文部科学大臣表彰 若手科学者賞

    2022.04   文部科学省  

    Winner: 市川幸平

  • MARCEL GROSSMANN AWARDS

    2021.06   MARCEL GROSSMANN Meeting  

    Winner: Max Planck Institute For Extraterrestrial Physics (to all members)

  • Prominent research fellow

    2021.06   Tohoku University  

    Winner: Kohei Ichikawa

 

Papers

  • Black Hole Mass and Eddington-ratio Distributions of Less-luminous Quasars at z ∼ 4 in the Subaru Hyper Suprime-Cam Wide Field

    Wanqiu He, Masayuki Akiyama, Motohiro Enoki, Kohei Ichikawa, Kohei Inayoshi, Nobunari Kashikawa, Toshihiro Kawaguchi, Yoshiki Matsuoka, Tohru Nagao, Masafusa Onoue, Taira Oogi, Andreas Schulze, Yoshiki Toba, Yoshihiro Ueda

    The Astrophysical Journal    2024.02

    DOI

    Scopus

  • Origin of an orbiting star around the galactic supermassive black hole

    Shogo Nishiyama, Tomohiro Kara, Brian Thorsbro, Hiromi Saida, Yohsuke Takamori, Masaaki Takahashi, Takayuki Ohgami, Kohei Ichikawa, Rainer Schödel

    Proceedings of the Japan Academy. Series B, Physical and biological sciences   100 ( 1 ) 86 - 99  2024.01

     View Summary

    The tremendous tidal force that is linked to the supermassive black hole (SMBH) at the center of our galaxy is expected to strongly subdue star formation in its vicinity. Stars within 1'' from the SMBH thus likely formed further from the SMBH and migrated to their current positions. In this study, spectroscopic observations of the star S0-6/S10, one of the closest (projected distance from the SMBH of ≈0''.3) late-type stars were conducted. Using metal absorption lines in the spectra of S0-6, the radial velocity of S0-6 from 2014 to 2021 was measured, and a marginal acceleration was detected, which indicated that S0-6 is close to the SMBH. The S0-6 spectra were employed to determine its stellar parameters including temperature, chemical abundances ([M/H], [Fe/H], [α/Fe], [Ca/Fe], [Mg/Fe], [Ti/Fe]), and age. As suggested by the results of this study, S0-6 is very old (≳10 Gyr) and has an origin different from that of stars born in the central pc region.

    DOI PubMed

    Scopus

  • The eROSITA final equatorial-depth survey (eFEDS): host-galaxy demographics of X-ray AGNs with Subaru Hyper Suprime-Cam

    Junyao Li, John D. Silverman, Andrea Merloni, Mara Salvato, Johannes Buchner, Andy Goulding, Teng Liu, Riccardo Arcodia, Johan Comparat, Xuheng Ding, Kohei Ichikawa, Masatoshi Imanishi, Toshihiro Kawaguchi, Lalitwadee Kawinwanichakij, Yoshiki Toba

    Monthly Notices of the Royal Astronomical Society   527 ( 3 ) 4690 - 4704  2024.01

     View Summary

    We investigate the physical properties, such as star-forming activity, disc versus bulge nature, galaxy size, and obscuration of 3811 SRG/eROSITA-detected AGNs at 0.2 < z < 0.8 in the eFEDS field. Using Subaru Hyper Suprime-Cam imaging data in the grizy bands, we measure the structural and stellar properties for their host galaxies by performing a 2D AGN-host image decomposition. We find that (1) AGNs can contribute significantly to the total optical light down to log LX ∼ 42.5 erg s−1, thus ignoring the AGN component can significantly bias the structural measurements; (2) AGN hosts are predominately star-forming galaxies at log M ≲ 11.3 M; (3) the bulk of AGNs (64 per cent) reside in galaxies with significant stellar discs (Sérsic index n < 2), while their host galaxies become increasingly bulge dominated (n ∼ 4) and quiescent at log M ≿ 11.0 M; (4) the size–stellar mass relation of AGN hosts tends to lie between that of inactive (i.e. non-AGN) star-forming, and quiescent galaxies, suggesting that the physical mechanism responsible for building the central stellar density also efficiently fuel the black hole growth; (5) the hosts of X-ray unobscured AGNs are biased towards face-on systems, suggesting that some of the obscuration of the nuclei could come from galaxy-scale gas and dust. This will bias against the detection of unobscured AGNs in gas-rich star-forming galaxies, which may partly account for the deficiency of star-forming discs as host galaxies for the most massive AGNs (missing star-forming fraction up to ∼ 40 per cent). Our results are consistent with a scenario in which the black hole and galaxy transform in structure and star-forming activity while grow in mass, as desired to establish the local MBH − Mbulge relation.

    DOI

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  • BASS. XLII. The Relation between the Covering Factor of Dusty Gas and the Eddington Ratio in Nearby Active Galactic Nuclei

    C. Ricci, K. Ichikawa, M. Stalevski, T. Kawamuro, S. Yamada, Y. Ueda, R. Mushotzky, G. C. Privon, M. J. Koss, B. Trakhtenbrot, A. C. Fabian, L. C. Ho, D. Asmus, F. E. Bauer, C. S. Chang, K. K. Gupta, K. Oh, M. Powell, R. W. Pfeifle, A. Rojas, F. Ricci, M. J. Temple, Y. Toba, A. Tortosa, E. Treister, F. Harrison, D. Stern, C. M. Urry

    Astrophysical Journal   959 ( 1 )  2023.12

     View Summary

    Accreting supermassive black holes (SMBHs) located at the centers of galaxies are typically surrounded by large quantities of gas and dust. The structure and evolution of this circumnuclear material can be studied at different wavelengths, from the submillimeter to the X-ray. Recent X-ray studies have shown that the covering factor of the obscuring material tends to decrease with increasing Eddington ratio, likely due to radiative feedback on dusty gas. Here we study a sample of 549 nearby (z ≲ 0.1) hard X-ray (14-195 keV) selected nonblazar active galactic nuclei (AGN) and use the ratio between the AGN infrared and bolometric luminosity as a proxy of the covering factor. We find that, in agreement with what has been found by X-ray studies of the same sample, the covering factor decreases with increasing Eddington ratio. We also confirm previous findings that showed that obscured AGN typically have larger covering factors than unobscured sources. Finally, we find that the median covering factors of AGN located in different regions of the column density-Eddington ratio diagram are in good agreement with what would be expected from a radiation-regulated growth of SMBHs.

    DOI

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  • BASS. XXXIV. A Catalog of the Nuclear Millimeter-wave Continuum Emission Properties of AGNs Constrained on Scales ≤ 100–200 pc

    Taiki Kawamuro, Claudio Ricci, Richard F. Mushotzky, Masatoshi Imanishi, Franz E. Bauer, Federica Ricci, Michael J. Koss, George C. Privon, Benny Trakhtenbrot, Takuma Izumi, Kohei Ichikawa, Alejandra F. Rojas, Krista Lynne Smith, Taro Shimizu, Kyuseok Oh, Jakob S. den Brok, Shunsuke Baba, Mislav Baloković, Chin Shin Chang, Darshan Kakkad, Ryan W. Pfeifle, Matthew J. Temple, Yoshihiro Ueda, Fiona Harrison, Meredith C. Powell, Daniel Stern, Meg Urry, David B. Sanders

    Astrophysical Journal, Supplement Series   269 ( 1 )  2023.11

     View Summary

    We present a catalog of the millimeter-wave (mm-wave) continuum properties of 98 nearby (z < 0.05) active galactic nuclei (AGNs) selected from the 70 month Swift/BAT hard-X-ray catalog that have precisely determined X-ray spectral properties and subarcsecond-resolution Atacama Large Millimeter/submillimeter Array Band 6 (211–275 GHz) observations as of 2021 April. Due to the hard-X-ray (>10 keV) selection, the sample is nearly unbiased for obscured systems at least up to Compton-thick-level obscuration, and provides the largest number of AGNs with high-physical-resolution mm-wave data (<100–200 pc). Our catalog reports emission peak coordinates, spectral indices, and peak fluxes and luminosities at 1.3 mm (230 GHz). Additionally, high-resolution mm-wave images are provided. Using the images and creating radial surface brightness profiles of mm-wave emission, we identify emission extending from the central sources and isolated blob-like emission. Flags indicating the presence of these emission features are tabulated. Among 90 AGNs with significant detections of nuclear emission, 37 AGNs (≈41%) appear to have both or one of extended or blob-like components. We, in particular, investigate AGNs that show well-resolved mm-wave components and find that these seem to have a variety of origins (i.e., a jet, radio lobes, a secondary AGN, stellar clusters, a narrow-line region, galaxy disk, active star formation regions, or AGN-driven outflows), and some components have currently unclear origins.

    DOI

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  • Digitization of weather records of Seungjeongwon Ilgi: A historical weather dynamics dataset of the Korean Peninsula in 1623–1910

    Zeyu Lyu, Kohei Ichikawa, Yongchao Cheng, Hisashi Hayakawa, Yukiko Kawamoto

    Geoscience Data Journal    2023.10

     View Summary

    Abstract

    Historical weather records from Europe indicate that the Earth experienced substantial climate variability, which caused, for instance, the Little Ice Age and the global crisis in the period between the 14th and 19th centuries. However, it is still unclear how global this climate variability was because of the scarce meteorological data availability in other regions including East Asia, especially around the 17th century. In this context, Seungjeongwon Ilgi, a daily record of the Royal Secretariat of the Joseon Dynasty of Korea, is a precious source of historical meteorological records for the Korean Peninsula, as it covers 288 years of weather observations made during 1623–1910. We used the digital database of Seungjeongwon Ilgi to construct a machine‐readable weather condition dataset. To this end, we extracted valid weather information from the original weather description text and compiled them into pre‐defined weather categories. Additionally, we attempted to improve the usability of dataset by converting the reported dates in the traditional calendar system to those in the Gregorian calendar. Finally, we outlined promising implications of this dataset for meteorological and climatological studies, while describing the limitations of the dataset. Overall, future studies focusing on the climate and weather of the past could use this meteorological database for investigating long‐term climate variability. Our datasets are publicly available at 10.5281/zenodo.8382243.

    DOI

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  • BASS. XXXV. The M <inf>BH</inf>-σ* Relation of 105 Month Swift-BAT Type 1 AGNs

    Turgay Caglar, Michael J. Koss, Leonard Burtscher, Benny Trakhtenbrot, M. Kiyami Erdim, Julian E. Mejía-Restrepo, Federica Ricci, Meredith C. Powell, Claudio Ricci, Richard Mushotzky, Franz E. Bauer, Tonima T. Ananna, Rudolf E. Bär, Bernhard Brandl, Jarle Brinchmann, Fiona Harrison, Kohei Ichikawa, Darshan Kakkad, Kyuseok Oh, Rogério Riffel, Lia F. Sartori, Krista L. Smith, Daniel Stern, C. Megan Urry

    Astrophysical Journal   956 ( 1 )  2023.10

     View Summary

    We present two independent measurements of stellar velocity dispersions (σ ⋆) from the Ca ii H+K λ3969, 3934 and Mg i b λ 5183, 5172, 5167 region (3880-5550 Å) and the calcium triplet region (8350-8750 Å) for 173 hard X-ray-selected Type 1 active galactic nuclei (AGNs; z ≤ 0.08) from the 105 month Swift-BAT catalog. We construct one of the largest samples of local Type 1 AGNs that have both single-epoch virial black hole mass (M BH) estimates and σ ⋆ measurements obtained from high spectral resolution data, allowing us to test the usage of such methods for supermassive black hole studies. We find that the two independent σ ⋆ measurements are highly consistent with each other, with an average offset of only 0.002 ± 0.001 dex. Comparing M BH estimates based on broad emission lines and stellar velocity dispersion measurements, we find that the former is systematically lower by ≈0.12 dex. Consequently, Eddington ratios estimated through broad-line M BH determinations are similarly biased (but in the opposite way). We argue that the discrepancy is driven by extinction in the broad-line region. We also find an anticorrelation between the offset from the M BH-σ ⋆ relation and the Eddington ratio. Our sample of Type 1 AGNs shows a shallower M BH-σ ⋆ relation (with a power-law exponent of ≈3.5) compared with that of inactive galaxies (with a power-law exponent of ≈4.5), confirming earlier results obtained from smaller samples.

    DOI

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  • eROSITA Final Equatorial-Depth Survey (eFEDS) eFEDS X-ray view of WERGS radio galaxies selected by the Subaru/HSC and VLA/FIRST survey

    Kohei Ichikawa, Takuji Yamashita, Andrea Merloni, Junyao Li, Teng Liu, Mara Salvato, Masayuki Akiyama, Riccardo Arcodia, Tom Dwelly, Xiaoyang Chen, Masatoshi Imanishi, Kohei Inayoshi, Toshihiro Kawaguchi, Taiki Kawamuro, Mitsuru Kokubo, Yoshiki Matsuoka, Tohru Nagao, Malte Schramm, Hyewon Suh, Masayuki Tanaka, Yoshiki Toba, Yoshihiro Ueda

    ASTRONOMY & ASTROPHYSICS   672  2023.04  [Refereed]

    Authorship:Lead author, Corresponding author

     View Summary

    yWe constructed the eROSITA X-ray catalog of radio galaxies discovered by the WERGS survey, made by cross-matching the wide area Subaru/Hyper Suprime-Cam (HSC) optical survey and VLA/FIRST 1.4 GHz radio survey. We report finding 393 eROSITA detected radio galaxies in the 0.5 2 keV band in the eFEDS field covering 140 deg(2). Thanks to the wide and medium depth eFEDS X-ray survey down to f(0.5-2 keV) = 6 :5 x10-(15) erg s(-1) cm(-2), the sample contains the rare and most X-ray luminous radio galaxies above the knee of the X-ray luminosity function, spanning 44 < log(L0.5-2keV ((abs,corr)) /ergs(-1)) < 46:5 at 1 < z < 4. The sample also contains the sources around and below the knee for the sources 41 < log(L0.5-2keV((abs,corr)) /ergs(-1) < 45 at z < 1. Based on the X-ray properties obtained by the spectral fitting, 37 sources show obscured active galactic nucleus (AGN) signatures with log(N-H =cm(-2)) > 22. These obscured and radio AGN reside in 0:4 < z < 3:2, indicating that they are obscured counterparts of the radio-loud quasar, which were missed in the previous optical quasar surveys. By combining radio and X-ray luminosities, we also investigated the jet production efficiency eta(jet) = eta P-rad(jet) / L-AGN;bol by utilizing the jet power of P-jet. We find that there are 14 sources with extremely high jet production efficiency at eta(jet) approximate to 1. This high eta(jet) value might be a result of the decreased radiation efficiency of eta(rad) < 0:1, due to the low accretion rate for those sources, and /or of the boosting due to the decline of LAGN;bol by a factor of 10 100 by keeping Pjet constant in the previous Myr, indicating the experience of the AGN feedback. Finally, inferring the BH masses from the stellar mass, we find that X-ray luminous sources show the excess of the radio emission with respect to the value estimated from the fundamental plane. This radio emission excess cannot be explained by the Doppler boosting alone, and therefore the disk-jet connection of X-ray luminous eFEDS-WERGS is fundamentally different from the conventional fundamental plane which mainly covers the low-accretion regime.

    DOI

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  • Massive Molecular Gas Companions Uncovered by Very Large Array CO(1-0) Observations of the z=5.2 Radio Galaxy TN J0924-2201

    Kianhong Lee, Kotaro Kohno, Bunyo Hatsukade, Fumi Egusa, Takuji Yamashita, Malte Schramm, Kohei Ichikawa, Masatoshi Imanishi, Takuma Izumi, Tohru Nagao, Yoshiki Toba, Hideki Umehata

    ASTROPHYSICAL JOURNAL   944 ( 1 )  2023.02  [Refereed]

     View Summary

    We present Karl G. Jansky Very Large Array K-band (19 GHz) observations of the redshifted CO(1-0) line emission toward the radio galaxy TN J0924-2201 at z = 5.2, which is one of the most distant radio galaxies with CO detected. With an angular resolution of similar to 2 '', the CO(1-0) line emission is resolved into three clumps, within +/- 500 km s(-1) relative to its redshift, which is determined by Ly alpha. We find that the clumps are located off-center and 12-33 kpc away from the center of the host galaxy, which has counterparts in the Hubble Space Telescope i band, Spitzer/IRAC, and the Atacama Large Millimeter/submillimeter Array (ALMA) band 6 (230 GHz; 1.3 mm). With the ALMA detection, we estimate the infrared luminosity LIR and the star formation rate (SFR) of the host galaxy to be (9.3 +/- 1.7) x 10(11)L(circle dot) and 110 +/- 20 M-circle dot yr(-1), respectively. We also derive the 3 sigma upper limit of M-H2 < 1.3 x 10(10) M-circle dot at the host galaxy. The 2 detected CO(1-0) line luminosities of the three clumps, L '(CO (1-0)) = (3.2-4.7) x 10(10) K km s(-1) pc(2), indicate the presence of three massive molecular gas reservoirs, with M-H2 = (2.5-3.7) x 10(10) M-circle dot, assuming a CO-to-H-2 conversion factor of alpha(CO) = 0.8 M-circle dot (K km s(-1) pc(2))(-1), although the SFR is not elevated due to the nondetection of the ALMA -1.3 mm continuum (SFR < 40 M-circle dot yr(-1)). From the host galaxy, the nearest molecular gas clump, labeled "clump A," is apparently in alignment with the radio jet axis, showing radio-CO alignment. The origins of these three clumps around TN J0924-2201 can possibly be interpreted as outflows, mergers, or jet-induced metal enrichment.

    DOI

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  • Extreme Nature of Four Blue-excess Dust-obscured Galaxies Revealed by Optical Spectroscopy

    Akatoki Noboriguchi, Tohru Nagao, Yoshiki Toba, Kohei Ichikawa, Masaru Kajisawa, Nanako Kato, Toshihiro Kawaguchi, Hideo Matsuhara, Yoshiki Matsuoka, Kyoko Onishi, Masafusa Onoue, Nozomu Tamada, Koki Terao, Yuichi Terashima, Yoshihiro Ueda, Takuji Yamashita

    The Astrophysical Journal   941   195  2022.12  [Refereed]

    DOI

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  • A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). IX. The most overdense region at z ∼ 5 inhabited by a massive radio galaxy

    Hisakazu Uchiyama, Takuji Yamashita, Tohru Nagao, Yoshiaki Ono, Jun Toshikawa, Kohei Ichikawa, Nozomu Kawakatu, Masaru Kajisawa, Yoshiki Toba, Yoshiki Matsuoka, Mariko Kubo, Masatoshi Imanishi, Kei Ito, Toshihiro Kawaguchi, Chien-Hsiu Lee, Tomoki Saito

    Publications of the Astronomical Society of Japan   74 ( 6 ) L27 - L32  2022.12  [Refereed]

     View Summary

    Abstract

    We report on the galaxy density environment around a high-z radio galaxy (HzRG) at z = 4.72, HSC J083913.17+011308.1 (HSC J0839+0113), probed using an r-dropout Lyman break galaxy (LBG) sample from the Hyper Suprime-Cam Subaru Strategic Program data. We find that HSC J0839+0113 resides in the outskirts of an overdense region identified by the r-dropout galaxies at a 4.7σ significance level. The projected distance between HSC J0839+0113 and the peak position of the overdense region is 0.4 physical Mpc, which is shorter than the typical protocluster radius in this epoch. According to the extended Press–Schechter and the light cone models, the HSC J0839+0113-hosted overdense region is expected to evolve into a halo &amp;gt;1014 ${M_{\odot } }$ at z = 0 with a high probability of $&amp;gt;\!\! 80\%$. These findings suggest that HSC J0839+0113 is associated with a protocluster. The HSC J0839+0113 rich-system is the most overdense region of LBGs among the known protoclusters with LBGs in the same cosmic epoch.

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  • H1821+643: The Most X-Ray and Infrared Luminous Active Galactic Nucleus (AGN) in the Swift/BAT Survey in the Process of Rapid Stellar and Supermassive Black Hole Mass Assembly

    Hikaru Fukuchi, Kohei Ichikawa, Masayuki Akiyama, Claudio Ricci, Sunmyon Chon, Mitsuru Kokubo, Ang Liu, Takuya Hashimoto, Takuma Izumi

    ASTROPHYSICAL JOURNAL   940 ( 1 )  2022.11  [Refereed]

    Authorship:Corresponding author

     View Summary

    H1821+643 is the most X-ray luminous nonbeamed active galactic nucleus (AGN) of L (14-150 keV) = 5.2 x 10(45) erg s(-1) in the Swift/Burst Alert Telescope (BAT) ultrahard X-ray survey, and it is also a hyperluminous infrared (IR) galaxy L (IR) = 10(13.2) L (& ODOT;) residing in the center of a massive galaxy cluster, which is a unique environment achieving the rapid mass assembly of black holes (BH) and host galaxies in the local universe. We decompose the X-ray to IR spectral energy distribution (SED) into the AGN and starburst component using the SED-fitting tool CIGALE-2022.0 and show that H1821+643 consumes a large amount of cold gas ( M?con 7 to 10(2) K thanks to [O i] 63 mu m, which is a main coolant in low temperature range (10(4) to 10(2) K) with a cooling rate of M?cool=3.2x105M & ODOT;yr-1

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  • BASS XXXII: Studying the Nuclear Millimeter-wave Continuum Emission of AGNs with ALMA at Scales ≲100–200 pc

    Taiki Kawamuro, Claudio Ricci, Masatoshi Imanishi, Richard F. Mushotzky, Takuma Izumi, Federica Ricci, Franz E. Bauer, Michael J. Koss, Benny Trakhtenbrot, Kohei Ichikawa, Alejandra F. Rojas, Krista Lynne Smith, Taro Shimizu, Kyuseok Oh, Jakob S. den Brok, Shunsuke Baba, Mislav Baloković, Chin-Shin Chang, Darshan Kakkad, Ryan W. Pfeifle, George C. Privon, Matthew J. Temple, Yoshihiro Ueda, Fiona Harrison, Meredith C. Powell, Daniel Stern, Meg Urry, David B. Sanders

    The Astrophysical Journal   938 ( 1 ) 87 - 87  2022.10  [Refereed]

     View Summary

    Abstract

    To understand the origin of nuclear (≲100 pc) millimeter-wave (mm-wave) continuum emission in active galactic nuclei (AGNs), we systematically analyzed subarcsecond resolution Band-6 (211–275 GHz) Atacama Large Millimeter/submillimeter Array data of 98 nearby AGNs (z &lt; 0.05) from the 70 month Swift/BAT catalog. The sample, almost unbiased for obscured systems, provides the largest number of AGNs to date with high mm-wave spatial resolution sampling (∼1–200 pc), and spans broad ranges of 14–150 keV luminosity {$40\lt \mathrm{log}[{L}_{14-150}/(\mathrm{erg}\,{ { \rm{s } } }^{-1})]\lt 45$}, black hole mass $[5\lt \mathrm{log}({M}_{\mathrm{BH } }/{M}_{\odot })\lt 10$], and Eddington ratio ($-4\lt \mathrm{log}{\lambda }_{\mathrm{Edd } }\lt 2$). We find a significant correlation between 1.3 mm (230 GHz) and 14–150 keV luminosities. Its scatter is ≈0.36 dex, and the mm-wave emission may serve as a good proxy of the AGN luminosity, free of dust extinction up to NH ∼ 1026 cm−2. While the mm-wave emission could be self-absorbed synchrotron radiation around the X-ray corona according to past works, we also discuss different possible origins of the mm-wave emission: AGN-related dust emission, outflow-driven shocks, and a small-scale (&lt;200 pc) jet. The dust emission is unlikely to be dominant, as the mm-wave slope is generally flatter than expected. Also, due to no increase in the mm-wave luminosity with the Eddington ratio, a radiation-driven outflow model is possibly not the common mechanism. Furthermore, we find independence of the mm-wave luminosity on indicators of the inclination angle from the polar axis of the nuclear structure, which is inconsistent with a jet model whose luminosity depends only on the angle.

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  • Finding of a Population of Active Galactic Nuclei Showing a Significant Luminosity Decline in the Past ∼103–104 yr

    Janek Pflugradt, Kohei Ichikawa, Masayuki Akiyama, Mitsuru Kokubo, Bovornpractch Vijarnwannaluk, Hirofumi Noda, Xiaoyang Chen

    The Astrophysical Journal   938 ( 1 ) 75 - 75  2022.10  [Refereed]

    Authorship:Corresponding author

     View Summary

    Abstract

    Recent observations have revealed an interesting active galactic nucleus (AGN) subclass that shows strong activity at large scales (∼1 kpc) but weaker at small scales (&lt;10 pc), suggesting a strong change in the mass accretion rate of the central engine in the past 103–104 yr. We systematically search for such declining or fading AGNs by cross-matching the Sloan Digital Sky Survey type 1 AGN catalog at z &lt; 0.4, covering the [O iii] λ5007 emission line, which is a tracer for the narrow-line region emission, with the Wide-field Infrared Survey Explorer (WISE) mid-infrared (MIR) catalog covering the emissions from the dusty tori. Out of the 7653 sources, we found 57 AGNs whose bolometric luminosities estimated from the MIR band are at least one order of magnitude fainter than those estimated from the [O iii] λ5007 emission line. This luminosity-declining AGN candidate population shows four important properties: (1) the past AGN activity estimated from the [O iii] λ5007 line reaches approximately the Eddington limit; (2) more than 30% of the luminosity-declining AGN candidates show a large absolute variability of ΔW1 &gt; 0.45 mag in the previous ∼10 yr at the WISE 3.4 μm band; (3) the median ratio of log([N ii] λ6584/Hαλ6563) = −0.52, suggesting a lower gas metallicity and/or higher ionization parameter compared to other AGN populations; and (4) the second-epoch spectra of the population indicate a spectral type change for 15% of the sources. This population provides insights on the possible connection between the luminosity decline that started ∼103–104 yr ago and the decline in the recent 10 yr.

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  • Mid-infrared and Maser Flux Variability Correlation in Massive Young Stellar Object G036.70+00.09

    Mizuho Uchiyama, Kohei Ichikawa, Koichiro Sugiyama, Yoshihiro Tanabe, Yoshinori Yonekura

    ASTROPHYSICAL JOURNAL   936 ( 1 )  2022.09  [Refereed]

     View Summary

    We present the discovery of the simultaneous flux variation of a massive young stellar object (MYSO) G036.70+00.09 (G036.70) both in the maser emission and mid-infrared (MIR; lambda = 3-5 mu m) bands. Using the ALLWISE and NEOWISE archival databases that cover a long time span of approximately 10 yr with a cadence of 6 months, we confirm that G036.70 indicates a stochastic year-long MIR variability with no signs of a WISE band color change of W1 (3.4 mu m) -W2 (4.6 mu m). Cross-matching the MIR data set with the high-cadence 6.7 GHz class II methanol maser flux using the Hitachi 32 m radio telescope that discovered its periodicity in the methanol maser of 53.0-53.2 days, we also determine the flux correlations between the two bands at two different timescales, year-long and day-long, both of which have never been reported in MYSOs, except when they are in the accretion burst phase. The results of our study support the scenario that a class II methanol maser is pumped up by infrared emission from accreting disks of MYSOs. We also discuss the possible origins of MIR and maser variability. To explain the two observed phenomena, a stochastic year-long MIR variability with no signs of significant color change and maser-MIR variability correlation or a change in mass accretion rate and line-of-sight extinction because of the nonaxisymmetric dust density distribution in a rotating accretion disk are possible origins. Observations through spectroscopic monitoring of accretion-related emission lines are essential for determining the origin of the observed variability in G036.70.

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  • BASS. XXX. Distribution Functions of DR2 Eddington Ratios, Black Hole Masses, and X-Ray Luminosities

    Tonima Tasnim Ananna, Anna K. Weigel, Benny Trakhtenbrot, Michael J. Koss, C. Megan Urry, Claudio Ricci, Ryan C. Hickox, Ezequiel Treister, Franz E. Bauer, Yoshihiro Ueda, Richard Mushotzky, Federica Ricci, Kyuseok Oh, Julian E. Mejia-Restrepo, Jakob Den Brok, Daniel Stern, Meredith C. Powell, Turgay Caglar, Kohei Ichikawa, O. Ivy Wong, Fiona A. Harrison, Kevin Schawinski

    ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES   261 ( 1 )  2022.07  [Refereed]

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    We determine the low-redshift X-ray luminosity function, active black hole mass function (BHMF), and Eddington ratio distribution function (ERDF) for both unobscured (Type 1) and obscured (Type 2) active galactic nuclei (AGNs), using the unprecedented spectroscopic completeness of the BAT AGN Spectroscopic Survey (BASS) data release 2. In addition to a straightforward 1/V-ma(x) approach, we also compute the intrinsic distributions, accounting for sample truncation by employing a forward-modeling approach to recover the observed BHMF and ERDF. As previous BHMFs and ERDFs have been robustly determined only for samples of bright, broad-line (Type 1) AGNs and/or quasars, ours are the first directly observationally constrained BHMF and ERDF of Type 2 AGNs. We find that after accounting for all observational biases, the intrinsic ERDF of Type 2 AGNs is significantly more skewed toward lower Eddington ratios than the intrinsic ERDF of Type 1 AGNs. This result supports the radiation-regulated unification scenario, in which radiation pressure dictates the geometry of the dusty obscuring structure around an AGN. Calculating the ERDFs in two separate mass bins, we verify that the derived shape is consistent, validating the assumption that the ERDF (shape) is mass-independent. We report the local AGN duty cycle as a function of mass and Eddington ratio, by comparing the BASS active BHMF with the local mass function for all supermassive black holes. We also present the log N - log S of the Swift/BAT 70 month sources.

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  • BASS. XXVIII. Near-infrared Data Release 2: High-ionization and Broad Lines in Active Galactic Nuclei

    Jakob S. den Brok, Michael J. Koss, Benny Trakhtenbrot, Daniel Stern, Sebastiano Cantalupo, Isabella Lamperti, Federica Ricci, Claudio Ricci, Kyuseok Oh, Franz E. Bauer, Rogerio Riffel, Alberto Rodriguez-Ardila, Rudolf Baer, Fiona Harrison, Kohei Ichikawa, Julian E. Mejia-Restrepo, Richard Mushotzky, Meredith C. Powell, Rozenn Boissay-Malaquin, Marko Stalevski, Ezequiel Treister, C. Megan Urry, Sylvain Veilleux

    ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES   261 ( 1 )  2022.07  [Refereed]

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    We present the BAT AGN Spectroscopic Survey (BASS) Near-infrared Data Release 2 (DR2), a study of 168 nearby ((z) over bar = 0.04, z < 0.6) active galactic nuclei (AGN) from the all-sky Swift Burst Array Telescope X-ray survey observed with the Very Large Telescope (VLT)/X-shooter in the near-infrared (NIR; 0.8-2.4 mu m). We find that 49/109 (45%) Seyfert 2 and 35/58 (60%) Seyfert 1 galaxies observed with VLT/X-shooter show at least one NIR high-ionization coronal line (CL; ionization potential chi > 100 eV). Comparing the emission of the [Si VI] lambda 1.9640 CL with the X-ray emission for the DR2 AGN, we find a significantly tighter correlation, with a lower scatter (0.37 dex) than that for the optical [O III] lambda 5007 line (0.71 dex). We do not find any correlation between CL emission and the X-ray photon index Gamma. We find a clear trend of line blueshifts with increasing ionization potential in several CLs, such as [Si VI] lambda 1.9640, [Si X] lambda 1.4300, [S VIII] lambda 0.9915, and [S IX] lambda 1.2520, indicating the radial structure of the CL region. Finally, we find a strong underestimation bias in black hole mass measurements of Sy 1.9 using broad H alpha due to the presence of significant dust obscuration. In contrast, the broad Pa alpha and Pa beta emission lines are in agreement with the M-sigma relation. Based on the combined DR1 and DR2 X-shooter sample, the NIR BASS sample now comprises 266 AGN with rest-frame NIR spectroscopic observations, the largest set assembled to date.

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  • BASS. XXII. The BASS DR2 AGN Catalog and Data

    Michael J. Koss, Claudio Ricci, Benny Trakhtenbrot, Kyuseok Oh, Jakob S. den Brok, Julian E. Mejia-Restrepo, Daniel Stern, George C. Privon, Ezequiel Treister, Meredith C. Powell, Richard Mushotzky, Franz E. Bauer, Tonima T. Ananna, Mislav Balokovic, Rudolf E. Bar, George Becker, Patricia Bessiere, Leonard Burtscher, Turgay Caglar, Enrico Congiu, Phil Evans, Fiona Harrison, Marianne Heida, Kohei Ichikawa, Nikita Kamraj, Isabella Lamperti, Fabio Pacucci, Federica Ricci, Rogerio Riffel, Alejandra F. Rojas, Kevin Schawinski, Matthew J. Temple, C. Megan Urry, Sylvain Veilleux, Jonathan Williams

    ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES   261 ( 1 )  2022.07  [Refereed]

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    We present the active galactic nucleus (AGN) catalog and optical spectroscopy for the second data release of the Swift BAT AGN Spectroscopic Survey (BASS DR2). With this DR2 release we provide 1449 optical spectra, of which 1182 are released for the first time, for the 858 hard-X-ray-selected AGNs in the Swift BAT 70-month sample. The majority of the spectra (801/1449, 55%) are newly obtained from Very Large Telescope (VLT)/X-shooter or Palomar/Doublespec. Many of the spectra have both higher resolution (R > 2500, N similar to 450) and/or very wide wavelength coverage (3200-10000 angstrom, N similar to 600) that are important for a variety of AGN and host galaxy studies. We include newly revised AGN counterparts for the full sample and review important issues for population studies, with 47 AGN redshifts determined for the first time and 790 black hole mass and accretion rate estimates. This release is spectroscopically complete for all AGNs (100%, 858/858), with 99.8% having redshift measurements (857/858) and 96% completion in black hole mass estimates of unbeamed AGNs (722/752). This AGN sample represents a unique census of the brightest hard-X-ray-selected AGNs in the sky, spanning many orders of magnitude in Eddington ratio (L/L (Edd) = 10(-5)-100), black hole mass (M (BH) = 10(5)-10(10) M (circle dot)), and AGN bolometric luminosity (L (bol) = 10(40)-10(47) erg s(-1) ).

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  • BASS. XXI. The Data Release 2 Overview

    Michael J. Koss, Benny Trakhtenbrot, Claudio Ricci, Franz E. Bauer, Ezequiel Treister, Richard Mushotzky, C. Megan Urry, Tonima T. Ananna, Mislay Balokovic, Jakob S. den Brok, S. Bradley Cenko, Fiona Harrison, Kohei Ichikawa, Isabella Lamperti, Amy Lein, Julian E. Mejia-Restrepo, Kyuseok Oh, Fabio Pacucci, Ryan W. Pfeifle, Meredith C. Powell, George C. Privon, Federica Ricci, Mara Salvato, Kevin Schawinski, Taro Shimizu, Krista L. Smith, Daniel Stern

    ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES   261 ( 1 )  2022.07  [Refereed]

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    The BAT AGN Spectroscopic Survey (BASS) is designed to provide a highly complete census of the key physical parameters of the supermassive black holes (SMBHs) that power local active galactic nuclei (AGNs) (z less than or similar to 0.3), including their bolometric luminosity (L (bol)), black hole (BH) mass (M (BH)), accretion rates (L (bol)/L (Edd)), line-of-sight gas obscuration (N (H)), and the distinctive properties of their host galaxies (e.g., star formation rates, masses, and gas fractions). We present an overview of the second data release of BASS (DR2), an unprecedented spectroscopic AGN survey in spectral range, resolution, and sensitivity, including 1449 optical (similar to 3200 angstrom-1 mu m) and 233 near-IR (1-2.5 mu m) spectra for the brightest 858 ultrahard X-ray (14-195 keV) selected AGNs across the entire sky and essentially all levels of obscuration. This release provides a highly complete set of key measurements (emission-line measurements and central velocity dispersions), with 99.9% measured redshifts and 98% BH masses estimated (for unbeamed AGNs outside the Galactic plane). The BASS DR2 AGN sample represents a unique census of nearby powerful AGNs, spanning over 5 orders of magnitude in AGN bolometric luminosity (L (bol) similar to 10(40)-10(47) erg s(-1)), BH mass (M (BH) similar to 10(5)-10(10) M (circle dot)), Eddington ratio (L (bol)/L (Edd) greater than or similar to 10(-5)), and obscuration (N (H) similar to 10(20)-10(25) cm(-2)). The public BASS DR2 sample and measurements can thus be used to answer fundamental questions about SMBH growth and its links to host galaxy evolution and feedback in the local universe, as well as open questions concerning SMBH physics. Here we provide a brief overview of the survey strategy, the key BASS DR2 measurements, data sets and catalogs, and scientific highlights from a series of DR2-based works pursued by the BASS team.

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  • BASS. XXV. DR2 Broad-line-based Black Hole Mass Estimates and Biases from Obscuration

    Julian E. Mejia-Restrepo, Benny Trakhtenbrot, Michael J. Koss, Kyuseok Oh, Jakob den Brok, Daniel Stern, Meredith C. Powell, Federica Ricci, Turgay Caglar, Claudio Ricci, Franz E. Bauer, Ezequiel Treister, Fiona A. Harrison, C. M. Urry, Tonima Tasnim Ananna, Daniel Asmus, Roberto J. Assef, Rudolf E. Baer, Patricia S. Bessiere, Leonard Burtscher, Kohei Ichikawa, Darshan Kakkad, Nikita Kamraj, Richard Mushotzky, George C. Privon, Alejandra F. Rojas, Eleonora Sani, Kevin Schawinski, Sylvain Veilleux

    ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES   261 ( 1 )  2022.07  [Refereed]

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    We present measurements of broad emission lines and virial estimates of supermassive black hole masses (M-BH) for a large sample of ultrahard X-ray-selected active galactic nuclei (AGNs) as part of the second data release of the BAT AGN Spectroscopic Survey (BASS/DR2). Our catalog includes M-BH estimates for a total of 689 AGNs, determined from the H alpha, H beta), Mg II lambda 2798, and/or C IV lambda 1549 broad emission lines. The core sample includes a total of 512 AGNs drawn from the 70 month Swift/BAT all-sky catalog. We also provide measurements for 177 additional AGNs that are drawn from deeper Swift/BAT survey data. We study the links between M-BH estimates and line-of-sight obscuration measured from X-ray spectral analysis. We find that broad Ha emission lines in obscured AGNs (log(N-H/cm(-2)) > 22.0) are on average a factor of 8.0(-2.4)(+4.1) weaker relative to ultrahard X-ray emission and about 35 + 1 7 2 % narrower than those in unobscured sources (i.e., log(N-H/cm(-2)) < 21.5). This indicates that the innermost part of the broad-line region is preferentially absorbed. Consequently, current single-epoch MBH prescriptions result in severely underestimated (>1 dex) masses for Type 1.9 sources (AGNs with broad Ha but no broad H beta)and/or sources with log(N-H/cm(-2)) greater than or similar to 22.0. We provide simple multiplicative corrections for the observed luminosity and width of the broad Ha component (L[bH alpha] and FWHM[bH alpha]) in such sources to account for this effect and to (partially) remedy MBH estimates for Type 1.9 objects. As a key ingredient of BASS/DR2, our work provides the community with the data needed to further study powerful AGNs in the low-redshift universe.

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  • BASS. XXIV. The BASS DR2 Spectroscopic Line Measurements and AGN Demographics

    Kyuseok Oh, Michael J. Koss, Yoshihiro Ueda, Daniel Stern, Claudio Ricci, Benny Trakhtenbrot, Meredith C. Powell, Jakob S. den Brok, Isabella Lamperti, Richard Mushotzky, Federica Ricci, Rudolf E. Bar, Alejandra F. Rojas, Kohei Ichikawa, Rogerio Riffel, Ezequiel Treister, Fiona Harrison, C. Megan Urry, Franz E. Bauer, Kevin Schawinski

    ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES   261 ( 1 )  2022.07  [Refereed]

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    We present the second catalog and data release of optical spectral line measurements and active galactic nucleus (AGN) demographics of the BAT AGN Spectroscopic Survey, which focuses on the Swift-BAT hard X-ray detected AGNs. We use spectra from dedicated campaigns and publicly available archives to investigate spectral properties of most of the AGNs listed in the 70 month Swift-BAT all-sky catalog; specifically, 743 of the 746 unbeamed and unlensed AGNs (99.6%). We find a good correspondence between the optical emission line widths and the hydrogen column density distributions using the X-ray spectra, with a clear dichotomy of AGN types for N (H) = 10(22) cm(-2). Based on optical emission-line diagnostics, we show that 48%-75% of BAT AGNs are classified as Seyfert, depending on the choice of emission lines used in the diagnostics. The fraction of objects with upper limits on line emission varies from 6% to 20%. Roughly 4% of the BAT AGNs have lines too weak to be placed on the most commonly used diagnostic diagram, [O iii]lambda 5007/H beta versus [N ii]lambda 6584/H alpha, despite the high signal-to-noise ratio of their spectra. This value increases to 35% in the [O iii]lambda 5007/[O ii]lambda 3727 diagram, owing to difficulties in line detection. Compared to optically selected narrow-line AGNs in the Sloan Digital Sky Survey, the BAT narrow-line AGNs have a higher rate of reddening/extinction, with H alpha/H beta > 5 (similar to 36%), indicating that hard X-ray selection more effectively detects obscured AGNs from the underlying AGN population. Finally, we present a subpopulation of AGNs that feature complex broad lines (34%, 250/743) or double-peaked narrow emission lines (2%, 17/743).

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  • BASS. XXIII. A New Mid-infrared Diagnostic for Absorption in Active Galactic Nuclei

    Ryan W. Pfeifle, Claudio Ricci, Peter G. Boorman, Marko Stalevski, Daniel Asmus, Benny Trakhtenbrot, Michael J. Koss, Daniel Stern, Federica Ricci, Shobita Satyapal, Kohei Ichikawa, David J. Rosario, Turgay Caglar, Ezequiel Treister, Meredith Powell, Kyuseok Oh, C. Megan Urry, Fiona Harrison

    ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES   261 ( 1 )  2022.07  [Refereed]

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    In this study, we use the Swift/BAT AGN sample, which has received extensive multiwavelength follow-up analysis as a result of the BAT AGN Spectroscopic Survey, to develop a diagnostic for nuclear obscuration by examining the relationship between the line-of-sight column densities (N-H), the 2-10 keV to 12 mu m luminosity ratio, and WISE mid-infrared colors. We demonstrate that heavily obscured AGNs tend to exhibit both preferentially "redder" mid-infrared colors and lower values of L-X,L-Obs./L-12 mu m than less obscured AGNs, and we derive expressions relating N-H to the L-X,L-Obs./L-12 mu m and L-22 mu m/L-4.6 mu m luminosity ratios, as well as develop diagnostic criteria using these ratios. Our diagnostic regions yield samples that are greater than or similar to 80% complete and greater than or similar to 60% pure for AGNs with log(N-H/cm(-2)) >= 24, as well as greater than or similar to 85% pure for AGNs with log(N-H/cm(-2)) greater than or similar to 23.5. We find that these diagnostics cannot be used to differentiate between optically star-forming galaxies and active galaxies. Further, mid-IR contributions from host galaxies that dominate the observed 12 mu m emission can lead to larger apparent X-ray deficits and redder mid-IR colors than the AGNs would intrinsically exhibit, though this effect helps to better separate less and more obscured AGNs. Finally, we test our diagnostics on two catalogs of AGNs and infrared galaxies, including the XMM-Newton XXL-N field, and we identify several known Compton-thick AGNs, as well as a handful of candidate heavily obscured AGNs based upon our proposed obscuration diagnostics.

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  • BASS. XXIX. The Near-infrared View of the Broad-line Region (BLR): The Effects of Obscuration in BLR Characterization*

    Federica Ricci, Ezequiel Treister, Franz E. Bauer, Julian E. Mejia-Restrepo, Michael J. Koss, Jakob S. den Brok, Mislav Balokovic, Rudolf Baer, Patricia Bessiere, Turgay Caglar, Fiona Harrison, Kohei Ichikawa, Darshan Kakkad, Isabella Lamperti, Richard Mushotzky, Kyuseok Oh, Meredith C. Powell, George C. Privon, Claudio Ricci, Rogerio Riffel, Alejandra F. Rojas, Eleonora Sani, Krista L. Smith, Daniel Stern, Benny Trakhtenbrot, C. Megan Urry, Sylvain Veilleux

    ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES   261 ( 1 )  2022.07  [Refereed]

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    Virial black hole (BH) mass (M (BH)) determination directly involves knowing the broad-line region (BLR) clouds' velocity distribution, their distance from the central supermassive BH (R (BLR)), and the virial factor (f). Understanding whether biases arise in M (BH) estimation with increasing obscuration is possible only by studying a large (N > 100) statistical sample of obscuration-unbiased (hard) X-ray-selected active galactic nuclei (AGNs) in the rest-frame near-infrared (0.8-2.5 mu m) since it penetrates deeper into the BLR than the optical. We present a detailed analysis of 65 local Burst Alert Telescope (BAT) selected Seyfert galaxies observed with Magellan/FIRE. Adding these to the near-infrared BAT AGN spectroscopic survey database, we study a total of 314 unique near-infrared spectra. While the FWHMs of H alpha and near-infrared broad lines (He i, Pa beta, Pa alpha) remain unbiased to either BLR extinction or X-ray obscuration, the H alpha broad-line luminosity is suppressed when N (H) greater than or similar to 10(21) cm(-2), systematically underestimating M (BH) by 0.23-0.46 dex. Near-infrared line luminosities should be preferred to H alpha until N (H) < 10(22) cm(-2), while at higher obscuration a less-biased R (BLR) proxy should be adopted. We estimate f for Seyfert 1 and 2 using two obscuration-unbiased M (BH) measurements, i.e., the stellar velocity dispersion and a BH mass prescription based on near-infrared and X-ray, and find that the virial factors do not depend on the redshift or obscuration, but some broad lines show a mild anticorrelation with M (BH). Our results show the critical impact obscuration can have on BLR characterization and the importance of the near-infrared and X-rays for a less-biased view of the BLR.

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  • A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). VII. Redshift Evolution of Radio Galaxy Environments at z=0.3-1.4

    Hisakazu Uchiyama, Takuji Yamashita, Tohru Nagao, Kohei Ichikawa, Yoshiki Toba, Shogo Ishikawa, Mariko Kubo, Masaru Kajisawa, Toshihiro Kawaguchi, Nozomu Kawakatu, Chien-Hsiu Lee, Akatoki Noboriguchi

    ASTROPHYSICAL JOURNAL   934 ( 1 )  2022.07  [Refereed]

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    We examine the redshift evolution of density environments around 2163 radio galaxies with the stellar masses of similar to 10(9)-10(12) M (circle dot) between redshifts of z = 0.3-1.4, based on the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) and Faint Images of the Radio Sky at Twenty cm. We use the k-nearest neighbor method to measure the local galaxy number density around our radio galaxy sample. We find that the overdensities of the radio galaxies are weakly but significantly anticorrelated with redshift. This is consistent with the known result that the relative abundance of less-massive radio galaxies increases with redshift, because less-massive radio galaxies reside in relatively low-density regions. Massive radio galaxies with stellar masses of M (*) > 10(11) M (circle dot) are found in high density environments compared with the control sample galaxies with radio nondetection and matched stellar mass. Less-massive radio galaxies with M (*) < 10(11) M (circle dot) reside in average density environments. The fraction of the radio galaxies associated with the neighbors within a typical major merger scale, <70 kpc, is higher than (comparable to) that of the control galaxies at M (*) > 10(11) M (circle dot) (M (*) < 10(11) M (circle dot)). We also find that the local densities around the radio galaxies are anticorrelated with the radio luminosities and black hole mass accretion rates at a fixed stellar mass. These findings suggest that massive radio galaxies have matured through galaxy mergers in the past, and have supermassive black holes whose mass accretion almost ceased at z > 1.4, while less-massive radio galaxies undergo active accretion just at this epoch, as they have avoided such merger events.

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  • The eROSITA Final Equatorial-Depth Survey (eFEDS) A multiwavelength view of WISE mid-infrared galaxies/active galactic nuclei

    Yoshiki Toba, Teng Liu, Tanya Urrutia, Mara Salvato, Junyao Li, Yoshihiro Ueda, Marcella Brusa, Naomichi Yutani, Keiichi Wada, Atsushi J. Nishizawa, Johannes Buchner, Tohru Nagao, Andrea Merloni, Masayuki Akiyama, Riccardo Arcodia, Bau-Ching Hsieh, Kohei Ichikawa, Masatoshi Imanishi, Kaiki T. Inoue, Toshihiro Kawaguchi, Georg Lamer, Kirpal Nandra, John D. Silverman, Yuichi Terashima

    ASTRONOMY & ASTROPHYSICS   661  2022.05  [Refereed]

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    Aims. We investigate the physical properties - such as the stellar mass (M-*), star-formation rate, infrared (IR) luminosity (L-IR), X-ray luminosity (L-X), and hydrogen column density (N-H) - of mid-IR (MIR) galaxies and active galactic nuclei (AGN) at z < 4 in the 140 deg(2) field observed by eROSITA on SRG using the Performance-and-Verification-Phase program named the eROSITA Final Equatorial Depth Survey (eFEDS).Methods. By cross-matching the WISE 22 mu m (W4)-detected sample and the eFEDS X-ray point-source catalog, we find that 692 extragalactic objects are detected by eROSITA. We have compiled a multiwavelength dataset extending from X-ray to far-IR wavelengths. We have also performed (i) an X-ray spectral analysis, (ii) spectral-energy-distribution fitting using X-CIGALE, (iii) 2D image-decomposition analysis using Subaru Hyper Suprime-Cam images, and (iv) optical spectral fitting with QSFit to investigate the AGN and host-galaxy properties. For 7088 WISE 22 tim objects that are undetected by eROSITA, we have performed an X-ray stacking analysis to examine the typical physical properties of these X-ray faint and probably obscured objects.Results. We find that (i) 82% of the eFEDS-W4 sources are classified as X-ray AGN with log L-X > 42 erg s(-1); (ii) 67 and 24% of the objects have log (L-IR/L-circle dot) > 12 and 13, respectively; (iii) the relationship between L-X and the 6 mu m luminosity is consistent with that reported in previous works; and (iv) the relationship between the Eddington ratio and N-H for the eFEDS-W4 sample and a comparison with a model prediction from a galaxy-merger simulation indicates that approximately 5.0% of the eFEDS-W4 sources in our sample are likely to be in an AGN-feedback phase, in which strong radiation pressure from the AGN blows out the surrounding material from the nuclear region.Conclusions. Thanks to the wide area coverage of eFEDS, we have been able to constrain the ranges of the physical properties of the WISE 22 mu m-selected sample of AGNs at z < 4, providing a benchmark for forthcoming studies on a complete census of MIR galaxies selected from the full-depth eROSITA all-sky survey.

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  • The eROSITA Final Equatorial-Depth Survey (eFEDS). Identification and characterization of the counterparts to point-like sources

    M. Salvato, J. Wolf, T. Dwelly, A. Georgakakis, M. Brusa, A. Merloni, T. Liu, Y. Toba, K. Nandra, G. Lamer, J. Buchner, C. Schneider, S. Freund, A. Rau, A. Schwope, A. Nishizawa, M. Klein, R. Arcodia, J. Comparat, B. Musiimenta, T. Nagao, H. Brunner, A. Malyali, A. Finoguenov, S. Anderson, Y. Shen, H. Ibarra-Medel, J. Trump, W. N. Brandt, C. M. Urry, C. Rivera, M. Krumpe, T. Urrutia, T. Miyaji, K. Ichikawa, D. P. Schneider, A. Fresco, T. Boller, J. Haase, J. Brownstein, R. R. Lane, D. Bizyaev, C. Nitschelm

    Astronomy and Astrophysics   661   A3 - A3  2022.05  [Refereed]

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    Context. In November 2019, eROSITA on board of the Spektrum-Roentgen-Gamma (SRG) observatory started to map the entire sky in X-rays. After the four-year survey program, it will reach a flux limit that is about 25 times deeper than ROSAT. During the SRG performance verification phase, eROSITA observed a contiguous 140 deg2 area of the sky down to the final depth of the eROSITA all-sky survey (eROSITA Final Equatorial-Depth Survey; eFEDS), with the goal of obtaining a census of the X-ray emitting populations (stars, compact objects, galaxies, clusters of galaxies, and active galactic nuclei) that will be discovered over the entire sky.

    Aims. This paper presents the identification of the counterparts to the point sources detected in eFEDS in the main and hard samples and their multi-wavelength properties, including redshift.

    Methods. To identifyy the counterparts, we combined the results from two independent methods (NWAY and ASTROMATCH), trained on the multi-wavelength properties of a sample of 23k XMM-Newton sources detected in the DESI Legacy Imaging Survey DR8. Then spectroscopic redshifts and photometry from ancillary surveys were collated to compute photometric redshifts.

    Results. Of the eFEDS sources, 24 774 of 27 369 have reliable counterparts (90.5%) in the main sample and 231 of 246 sourcess (93.9%) have counterparts in the hard sample, including 2514 (3) sources for which a second counterpart is equally likely. By means of reliable spectra, Gaia parallaxes, and/or multi-wavelength properties, we have classified the reliable counterparts in both samples into Galactic (2695) and extragalactic sources (22 079). For about 340 of the extragalactic sources, we cannot rule out the possibility that they are unresolved clusters or belong to clusters. Inspection of the distributions of the X-ray sources in various optical/IR colour-magnitude spaces reveal a rich variety of diverse classes of objects. The photometric redshifts are most reliable within the KiDS/VIKING area, where deep near-infrared data are also available.

    Conclusions. This paper accompanies the eROSITA early data release of all the observations performed during the performance and verification phase. Together with the catalogues of primary and secondary counterparts to the main and hard samples of the eFEDS survey, this paper releases their multi-wavelength properties and redshifts.

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  • The eROSITA Final Equatorial-Depth Survey (eFEDS) The AGN catalog and its X-ray spectral properties

    Teng Liu, Johannes Buchner, Kirpal Nandra, Andrea Merloni, Tom Dwelly, Jeremy S. Sanders, Mara Salvato, Riccardo Arcodia, Marcella Brusa, Julien Wolf, Antonis Georgakakis, Thomas Boller, Mirko Krumpe, Georg Lamer, Sophia Waddell, Tanya Urrutia, Axel Schwope, Jan Robrade, Joern Wilms, Thomas Dauser, Johan Comparat, Yoshiki Toba, Kohei Ichikawa, Kazushi Iwasawa, Yue Shen, Hector Ibarra Medel

    ASTRONOMY & ASTROPHYSICS   661  2022.05  [Refereed]

     View Summary

    Context. The eROSITA Final Equatorial Depth Survey (eFEDS), observed with eROSITA ahead of its planned 4-yr all-sky survey, is the largest contiguous-field X-ray survey at present. It yielded a large sample of X-ray sources with very rich multiband photometric and spectroscopic coverage.Aims. We present here the eFEDS active galactic nuclei (AGN) catalog and the eROSITA X-ray spectral properties of the eFEDS sources.Methods. Using a Bayesian method, we performed a systematic X-ray spectral analysis for all the eFEDS sources. We adopted multiple spectral models, including single-component power-law or hot-plasma models and double-component models of a power law plus soft excess. We investigated the capacity of eROSITA X-ray spectra for constraining AGN spectral shapes through a detailed analysis of the posterior parameter probability distribution functions. Hierarchical Bayesian modeling was used to recover the spectral parameter distribution of the sample. The source fluxes and luminosities were measured from the posterior of the spectral fitting.Results. The eFEDS AGN catalog (22 079 sources) comprises similar to 80% of the eFEDS point sources. Despite a large number of faint sources, our spectral fitting provides reasonable measurements of spectral shapes and intrinsic luminosities for a majority of the sources. Because of sample selection bias, this AGN catalog is dominated by X-ray unobscured sources, with an obscured (logN(H) > 21.5) fraction of 8%; the power-law emission of the hot corona is also relatively soft, with a typical slope of 2.0. For type-I AGN, the X-ray emission is well correlated with the UV emission with the usual anticorrelation between the X-ray to UV spectral slope alpha(OX) and the UV luminosity. The X-ray spectral properties measured with various models are presented for all the eFEDS sources.

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  • A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). VI. Distant Filamentary Structures Pointed Out by High-z Radio Galaxies at z ∼ 4

    Hisakazu Uchiyama, Takuji Yamashita, Jun Toshikawa, Nobunari Kashikawa, Kohei Ichikawa, Mariko Kubo, Kei Ito, Nozomu Kawakatu, Tohru Nagao, Yoshiki Toba, Yoshiaki Ono, Yuichi Harikane, Masatoshi Imanishi, Masaru Kajisawa, Chien-Hsiu Lee, Yongming Liang

    The Astrophysical Journal   926 ( 1 ) 76 - 76  2022.02  [Refereed]

     View Summary

    Abstract

    We present the environmental properties around high-z radio galaxies (HzRGs) at z ∼ 4, which have been poorly investigated because of their rarity. We use the largest samples of HzRGs and g-dropout galaxy overdense regions at z ∼ 4, which were constructed from the Hyper Suprime-Cam Subaru Strategic Program, to characterize the HzRG environments statistically. We measure the g-dropout galaxy overdensities around 21 HzRGs whose rest-frame 1.4 GHz radio luminosities (L1.4 GHz) are 1026–27 W Hz−1. We find that the overdensities around the faint HzRGs with L1.4 GHz ∼ 1026.0–26.5 W Hz−1 tend to be higher than those of the g-dropout galaxies. On the other hand, no significant difference of density environments is found between the luminous HzRGs with L1.4 GHz ∼ 1026.5–27.0 W Hz−1 and the g-dropout galaxies. The HzRGs are found to occupy more massive halos than g-dropout galaxies through a cross-correlation between the HzRGs and g-dropout galaxies. This trend is more pronounced in the faint HzRGs. These results are consistent with a scenario where HzRGs get older and more massive as the radio luminosity decreases. The HzRGs are expected to trace the progenitors of Local Cluster halos from their calculated halo mass. In addition, we find that surrounding galaxies tend to distribute along the radio jet major axis of the HzRGs at angular distances of ≲500 physical kpc. Our findings imply the onset of the filamentary structures around the HzRGs at z ∼ 4.

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  • Hypercubes of AGN Tori (HYPERCAT). II. Resolving the Torus with Extremely Large Telescopes

    Robert Nikutta, Enrique Lopez-Rodriguez, Kohei Ichikawa, N. A. Levenson, Christopher Packham, Sebastian F. Honig, Almudena Alonso-Herrero

    ASTROPHYSICAL JOURNAL   923 ( 1 )  2021.12  [Refereed]

     View Summary

    Recent infrared interferometric observations revealed sub-parsec scale dust distributions around active galactic nuclei (AGNs). Using images of Clumpy torus models and NGC 1068 as an example, we demonstrate that the near- and mid-infrared nuclear emission of some nearby AGNs will be resolvable in direct imaging with the next generation of 30 m telescopes, potentially breaking degeneracies from previous studies that used integrated spectral energy distributions of unresolved AGN tori. To that effect we model wavelength-dependent point spread functions from the pupil images of various telescopes: James Webb Space Telescope, Keck, Giant Magellan Telescope, Thirty Meter Telescope, and Extremely Large Telescope. We take into account detector pixel scales and noise, and apply deconvolution techniques for image recovery. We also model 2D maps of the 10 mu m silicate feature strength, S (10), of NGC 1068 and compare with observations. When the torus is resolved, we find S (10) variations across the image. However, to reproduce the S (10) measurements of an unresolved torus a dusty screen of A ( V ) > 9 mag is required. We also fit the first resolved image of the K-band emission in NGC 1068 recently published by the GRAVITY Collaboration, deriving likely model parameters of the underlying dust distribution. We find that both (1) an elongated structure suggestive of a highly inclined emission ring, and (2) a geometrically thin but optically thick flared disk where the emission arises from a narrow strip of hot cloud surface layers on the far inner side of the torus funnel, can explain the observations.

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  • A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). IV. Rapidly Growing (Super)Massive Black Holes in Extremely Radio-loud Galaxies

    Kohei Ichikawa, Takuji Yamashita, Yoshiki Toba, Tohru Nagao, Kohei Inayoshi, Maria Charisi, Wanqiu He, Alexander Y. Wagner, Masayuki Akiyama, Bovornpratch Vijarnwannaluk, Xiaoyang Chen, Masaru Kajisawa, Taiki Kawamuro, Chien-Hsiu Lee, Yoshiki Matsuoka, Malte Schramm, Hyewon Suh, Masayuki Tanaka, Hisakazu Uchiyama, Yoshihiro Ueda, Janek Pflugradt, Hikaru Fukuchi

    ASTROPHYSICAL JOURNAL   921 ( 1 )  2021.11  [Refereed]

    Authorship:Lead author, Corresponding author

     View Summary

    We present the optical and infrared properties of 39 extremely radio-loud galaxies discovered by cross-matching the Subaru/Hyper Suprime-Cam (HSC) deep optical imaging survey and VLA/FIRST 1.4 GHz radio survey. The recent Subaru/HSC strategic survey revealed optically faint radio galaxies (RG) down to g(AB) similar to 26, opening a new parameter space of extremely radio-loud galaxies (ERGs) with radio-loudness parameter of log R-rest log (f(1.4GHz,rest)/f(g,rest)) > 4. Because of their optical faintness and small number density of similar to 1 deg(-2), such ERGs were difficult to find in the previous wide but shallow or deep but small area optical surveys. ERGs show intriguing properties that are different from the conventional RGs: (1) most ERGs reside above or on the star-forming main-sequence and some of them might be low-mass galaxies with log(M-*/M-circle dot) < 10. (2) ERGs exhibit a high specific black hole accretion rate, reaching the order of the Eddington limit. The intrinsic radio loudness (R-int), defined by the ratio of jet power over bolometric radiation luminosity, is one order of magnitude higher than that of radio quasars. This suggests that ERGs harbor a unique type of active galactic nuclei (AGN) that show both powerful radiations and jets. Therefore, ERGs are prominent candidates of very rapidly growing black holes reaching Eddington-limited accretion just before the onset of intensive AGN feedback.

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  • Optical Spectroscopy of Dual Quasar Candidates from the Subaru HSC-SSP program

    Shenli Tang, John D. Silverman, Xuheng Ding, Junyao Li, Khee-Gan Lee, Michael A. Strauss, Andy Goulding, Malte Schramm, Lalitwadee Kawinwanichakij, J. Xavier Prochaska, Joseph F. Hennawi, Masatoshi Imanishi, Kazushi Iwasawa, Yoshiki Toba, Issha Kayo, Masamune Oguri, Yoshiki Matsuoka, Masafusa Onoue, Knud Jahnke, Kohei Ichikawa, Tilman Hartwig, Nobunari Kashikawa, Toshihiro Kawaguchi, Kotaro Kohno, Yuichi Matsuda, Tohru Nagao, Yoshiaki Ono, Masami Ouchi, Kazuhiro Shimasaku, Hyewon Suh, Nao Suzuki, Yoshiaki Taniguchi, Yoshihiro Ueda, Naoki Yasuda

    ASTROPHYSICAL JOURNAL   922 ( 1 )  2021.11  [Refereed]

     View Summary

    We report on a spectroscopic program to search for dual quasars using Subaru Hyper Suprime-Cam (HSC) images of SDSS quasars, which represent an important stage during galaxy mergers. Using Subaru/FOCAS and Gemini-N/GMOS, we identify three new physically associated quasar pairs having projected separations less than 20 kpc, out of 26 observed candidates. These include the discovery of the highest-redshift (z = 3.1) quasar pair with a separation <10 kpc. Based on the sample acquired to date, the success rate of identifying physically associated dual quasars is 19% when excluding stars based on their HSC colors. Using the full sample of six spectroscopically confirmed dual quasars, including three previously published, we find that the black holes in these systems have black hole masses (M (BH) similar to 10(8-9) M (circle dot)), bolometric luminosities (log L (bol) similar to 44.5-47.5 erg s(-1)) and Eddington ratios (0.01-0.3) similar to single SDSS quasars. We measure the stellar mass of their host galaxies based on 2D image decomposition of the five-band (grizy) optical emission and assess the mass relation between supermassive black holes (SMBHs) and their hosts. Dual SMBHs appear to have elevated masses relative to their host galaxies. Thus, mergers may not necessarily align such systems onto the local mass relation, as suggested by the Horizon-AGN simulation. This study suggests that dual luminous quasars are triggered by mergers prior to the final coalescence of the two SMBHs, resulting in early mass growth of the black holes relative to their host galaxies.

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  • Hypercubes of AGN Tori (HYPERCAT). I. Models and Image Morphology

    Robert Nikutta, Enrique Lopez-Rodriguez, Kohei Ichikawa, N. A. Levenson, Christopher Packham, Sebastian F. Honig, Almudena Alonso-Herrero

    ASTROPHYSICAL JOURNAL   919 ( 2 )  2021.10  [Refereed]

     View Summary

    Near- and mid-infrared interferometers have resolved the dusty parsec-scale obscurer (torus) around nearby active galactic nuclei (AGNs). With the arrival of extremely large single-aperture telescopes, the emission morphology will soon be resolvable unambiguously, without modeling directly the underlying brightness distribution probed by interferometers today. Simulations must instead deliver the projected 2D brightness distribution as a result of radiative transfer through a 3D distribution of dusty matter around the AGN. We employ such physically motivated 3D dust distributions in tori around AGNs to compute 2D images of the emergent thermal emission, using Clumpy, a dust radiative transfer code for clumpy media. We demonstrate that Clumpy models can exhibit morphologies with significant polar elongation in the mid-infrared (i.e., the emission extends perpendicular to the dust distribution) on scales of several parsecs, in line with observations in several nearby AGNs. We characterize the emission and cloud distribution morphologies. The observed emission from near- to mid-infrared wavelengths generally does not trace the bulk of the cloud distribution. The elongation of the emission is sensitive to the torus opening angle or scale height. For cloud distributions with a flat radial profile, polar extended emission is realized only at wavelengths shorter than similar to 18 mu m, and shorter than similar to 5 mu m for steep profiles. We make the full results available through Hypercat, a large hypercube of resolved AGN torus brightness maps computed with Clumpy. Hypercat also comprises software to process and analyze such large data cubes and provides tools to simulate observations with various current and future telescopes.

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  • The Galaxy Activity, Torus, and Outflow Survey (GATOS). I. ALMA images of dusty molecular tori in Seyfert galaxies

    S. García-Burillo, A. Alonso-Herrero, C. Ramos Almeida, O. González-Martín, F. Combes, A. Usero, S. Hönig, M. Querejeta, E. K. S. Hicks, L. K. Hunt, D. Rosario, R. Davies, P. G. Boorman, A. J. Bunker, L. Burtscher, L. Colina, T. Díaz-Santos, P. Gandhi, I. García-Bernete, B. García-Lorenzo, K. Ichikawa, M. Imanishi, T. Izumi, A. Labiano, N. A. Levenson, E. López-Rodríguez, C. Packham, M. Pereira-Santaella, C. Ricci, D. Rigopoulou, D. Rouan, T. Shimizu, M. Stalevski, K. Wada, D. Williamson

    Astronomy & Astrophysics   652   A98 - A98  2021.08  [Refereed]

     View Summary

    We present the first results of the Galaxy Activity, Torus, and Outflow Survey (GATOS), a project aimed at understanding the properties of the dusty molecular tori and their connection to the host galaxy in nearby Seyfert galaxies. Our project expands the range of active galactic nuclei (AGN) luminosities and Eddington ratios covered by previous surveys of Seyferts conducted by the Atacama Large Millimeter Array (ALMA), allowing us to study the gas feeding and feedback cycle in a combined sample of 19 Seyferts. We used ALMA to obtain new images of the emission of molecular gas and dust using the CO(3–2) and HCO+(4–3) lines as well as their underlying continuum emission at 870 μm with high spatial resolutions (0.1″ ∼ 7 − 13 pc) in the circumnuclear disks (CND) of ten nearby (<italic>D</italic> &lt; 28 Mpc) Seyfert galaxies selected from an ultra-hard X-ray survey. Our new ALMA observations detect 870 μm continuum and CO line emission from spatially resolved disks located around the AGN in all the sources. The bulk of the 870 μm continuum flux can be accounted for by thermal emission from dust in the majority of the targets. For most of the sources, the disks show a preponderant orientation perpendicular to the AGN wind axes, as expected for dusty molecular tori. The median diameters and molecular gas masses of the tori are ∼42 pc and ∼6 × 105 <italic>M</italic>, respectively. We also detected the emission of the 4–3 line of HCO+ in four GATOS targets. The order of magnitude differences found in the CO/HCO+ ratios within our combined sample point to a very different density radial stratification inside the dusty molecular tori of these Seyferts. We find a positive correlation between the line-of-sight gas column densities responsible for the absorption of X-rays and the molecular gas column densities derived from CO toward the AGN in our sources. Furthermore, the median values of both column densities are similar. This suggests that the neutral gas line-of-sight column densities of the dusty molecular tori imaged by ALMA significantly contribute to the obscuration of X-rays. The radial distributions of molecular gas in the CND of our combined sample show signs of nuclear-scale molecular gas deficits. We also detect molecular outflows in the sources that show the most extreme nuclear-scale gas deficits in our sample. These observations find for the first time supporting evidence that the imprint of AGN feedback is more extreme in higher luminosity and/or higher Eddington ratio Seyfert galaxies.

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  • The Galaxy Activity, Torus, and Outflow Survey (GATOS): II. Torus and polar dust emission in nearby Seyfert galaxies

    A. Alonso-Herrero, S. García-Burillo, S. F. Hönig, I. García-Bernete, C. Ramos Almeida, O. González-Martín, E. López-Rodríguez, P. G. Boorman, A. J. Bunker, L. Burtscher, F. Combes, R. Davies, T. Díaz-Santos, P. Gandhi, B. García-Lorenzo, E. K.S. Hicks, L. K. Hunt, K. Ichikawa, M. Imanishi, T. Izumi, A. Labiano, N. A. Levenson, C. Packham, M. Pereira-Santaella, C. Ricci, D. Rigopoulou, P. Roche, D. J. Rosario, D. Rouan, T. Shimizu, M. Stalevski, K. Wada, D. Williamson

    Astronomy and Astrophysics   652  2021.08  [Refereed]

     View Summary

    We compare high angular resolution mid-infrared (mid-IR) and Atacama Large Millimeter/submillimeter Array (ALMA) far-infrared (far-IR) images of twelve nearby (median 21 Mpc) Seyfert galaxies selected from the Galaxy Activity, Torus, and Outflow Survey (GATOS). The mid-IR unresolved emission contributes more than 60% of the nuclear (diameters of 1.5″ ∼ 150 pc) emission in most galaxies. By contrast, the ALMA 870  μm continuum emission is mostlyresolved with a median diameter of 42 pc and typically along the equatorial direction of the torus (Paper I). The Eddington ratios and nuclear hydrogen column densities (NH) of half the sample are favorable to launching polar and/or equatorial dusty winds, according to numerical simulations. Six of these show mid-IR extended emission approximately in the polar direction as traced by the narrow line region and perpendicular to the ALMA emission. In a few galaxies, the nuclear NH might be too high to uplift large quantities of dusty material along the polar direction. Five galaxies have low NH and/or Eddington ratios and thus polar dusty winds are not likely. We generated new radiative transfer CAT3D-WIND disk+wind models and model images at 8, 12, and 700  μm. We tailored these models to the properties of the GATOS Seyferts in this work. At low wind-to-disk cloud ratios, the far-IR model images have disk-and ring-like morphologies. The characteristic "X"-shape associated with dusty winds is seen better in the far-IR at intermediate-high inclinations for the extended-wind configurations. In most of the explored models, the mid-IR emission mainly comes from the inner part of the disk and cone. Extended biconical and one-sided polar mid-IR emission is seen in extended-wind configurations and high wind-to-disk cloud ratios. When convolved to the typical angular resolution of our observations, the CAT3D-WIND model images reproduce qualitative aspects of the observed mid-and far-IR morphologies. However, low to intermediate values of the wind-to-disk ratio are required to account for the observed large fractions of unresolved mid-IR emission in our sample. This work and Paper I provide observational support for the torus+wind scenario. The wind component is more relevant at high Eddington ratios and/or active galactic nucleus luminosities, and polar dust emission is predicted at nuclear column densities of up to ∼1024 cm-2. The torus or disk component, on the other hand, prevails at low luminosities and/or Eddington ratios.

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  • BAT AGN Spectroscopic Survey XXVII: Scattered X-Ray radiation in obscured active galactic nuclei

    K. K. Gupta, C. Ricci, A. Tortosa, Y. Ueda, T. Kawamuro, M. Koss, B. Trakhtenbrot, K. Oh, F. E. Bauer, F. Ricci, G. C. Privon, L. Zappacosta, D. Stern, D. Kakkad, E. Piconcelli, S. Veilleux, R. Mushotzky, T. Caglar, K. Ichikawa, A. Elagali, M. C. Powell, C. M. Urry, F. Harrison

    Monthly Notices of the Royal Astronomical Society   504 ( 1 ) 428 - 443  2021.06  [Refereed]

     View Summary

    Accreting supermassive black holes (SMBHs), also known as active galactic nuclei (AGN), are generally surrounded by large amounts of gas and dust. This surrounding material reprocesses the primary X-ray emission produced close to the SMBH and gives rise to several components in the broadband X-ray spectra of AGN, including a power-law possibly associated with Thomson-scattered radiation. In this work, we study the properties of this scattered component for a sample of 386 hard-X-ray-selected, nearby ($z\sim0.03$) obscured AGN from the 70-month Swift/BAT catalogue. We investigate how the fraction of Thomson-scattered radiation correlates with different physical properties of AGN, such as line-of-sight column density, X-ray luminosity, black hole mass, and Eddington ratio. We find a significant negative correlation between the scattering fraction and the column density. Based on a large number of spectral simulations, we exclude the possibility that this anticorrelation is due to degeneracies between the parameters. The negative correlation also persists when considering different ranges of luminosity, black hole mass, and Eddington ratio. We discuss how this correlation might be either due to the angle dependence of the Thomson cross-section or to more obscured sources having a higher covering factor of the torus. We also find a positive correlation between the scattering fraction and the ratio of [O iii] λ5007 to X-ray luminosity. This result is consistent with previous studies and suggests that the Thomson-scattered component is associated with the narrow-line region.

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  • Three Case Reports on the Cometary Plasma Tail in the Historical Documents

    Hisashi Hayakawa, Yuri Fujii, Koji Murata, Yasuyuki Mitsuma, Yongchao Cheng, Nagatoshi Nogami, Kohei Ichikawa, Hidetoshi Sano, Kohji Tsumura, Yukiko Kawamoto, Masaki Nishino

    Journal of Space Weather and Space Climate   11   21 - 21  2021.03  [Refereed]

     View Summary

    Cometary tails visually manifest the solar wind and became a first hint for its discovery. While the solar wind is being directly monitored with satellites, its time series before the space age has been controversially reconstructed with multiple proxies. Recently, cometary plasma tail observations have been subjected to consideration to indirectly measure the solar wind but brought conclusion that no plasma tail has been reported prior to 1769 probably due to their brightness. However, historical records have occasionally reported comets with two tails even before 1769 and these cases have been tentatively associated with visual reports of cometary plasma and dust tails. Therefore, we examined three such cases (C/1577 V1, 1P/837, and 1P/760), compared the descriptions in historical records with calculated direction of their plasma tails. Our comparisons show that the records and calculations agree in these cases and plasma tails were visually recorded corresponding to these three great comets. These cases certify the capability of plasma tail observations with the unaided eye even before 1769, qualitatively imply their extreme brightness, proximities with the Sun and the Earth, and relative enhancements of UV radiations and interaction of cometary neutral atmosphere with solar wind plasma and magnetic field, while the lack of their detailed length or kink hinders us from their quantitative measuring. Further investigations will probably lead to the re-discovery of even more visual evidence of cometary plasma tail and, hence, improve our understanding on past space climate.

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  • Cometary records revise Eastern Mediterranean chronology around 1240 CE

    Koji Murata, Kohei Ichikawa, Yuri I Fujii, Hisashi Hayakawa, Yongchao Cheng, Yukiko Kawamoto, Hidetoshi Sano

    Publications of the Astronomical Society of Japan   73 ( 1 ) 197 - 204  2021.02  [Refereed]

    Authorship:Corresponding author

     View Summary

    Eirene Laskarina, empress of John III Batatzes of the exiled Byzantine Empire
    of Nicaea (1204--1261 CE), was an important Eastern Mediterranean figure in the
    first half of the thirteenth century. We reassess the date of Eirene's death,
    which has been variously dated between late 1239 and 1241, with the
    understanding that narrowing the range in which this event occurred contributes
    much to understanding the political situation in the area around 1240. George
    Akropolites, a famous official of the Empire, gives an account that connects
    Eirene's death to a comet that appeared "six months earlier", thus pointing to
    two comet candidates that were visible from the Eastern Mediterranean between
    1239 and 1241, one recorded on "3 June 1239" and the other on "31 January
    1240". Recent historians prefer the former, based on historical circumstances
    and without a critical assessment of the comet records. We revisit the
    historical records and reveal that the "3 June 1239" candidate was not a comet.
    On the other hand, the other candidate, sighted on "31 January 1240", was a
    comet, as supported by multiple historical records in multiple regions, and is
    also a good fit with Akropolites's narrative. Therefore, we conclude that
    Eirene died six months after the comet that was seen on 31 January 1240, which
    places her death in the summer of 1240. Given that the date of her death is
    crucial for determining some other contemporary events across the Eastern
    Mediterranean, our results offer a solid basis for further research on the
    thirteenth-century Eastern Mediterranean.

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  • BAT AGN Spectroscopic Survey-XX: Molecular Gas in Nearby Hard X-ray Selected AGN Galaxies

    Michael J. Koss, Benjamin Strittmatter, Isabella Lamperti, Taro Shimizu, Benny Trakhtenbrot, Amelie Saintonge, Ezequiel Treister, Claudia Cicone, Richard Mushotzky, Kyuseok Oh, Claudio Ricci, Daniel Stern, Tonima T. Ananna, Franz E. Bauer, George C. Privon, Rudolf E. Bar, Carlos De Breuck, Fiona Harrison, Kohei Ichikawa, Meredith C. Powell, David Rosario, David B. Sanders, Kevin Schawinski, Li Shao, C. Megan Urry, Sylvain Veilleux

    ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES   252 ( 2 )  2021.02  [Refereed]

     View Summary

    We present the host galaxy molecular gas properties of a sample of 213 nearby
    (0.01<z< 0.05) hard X-ray selected AGN galaxies, drawn from the 70-month
    catalog of Swift-BAT, with 200 new CO(2-1) line measurements obtained with the
    JCMT and APEX telescopes. We find that AGN in massive galaxies tend to have
    more molecular gas, and higher gas fractions, than inactive galaxies matched in
    stellar mass. When matched in star formation, we find AGN galaxies show no
    difference from inactive galaxies with no evidence of AGN feedback affecting
    the molecular gas. The higher molecular gas content is related to AGN galaxies
    hosting a population of gas-rich early types with an order of magnitude more
    molecular gas and a smaller fraction of quenched, passive galaxies (~5% vs.
    49%). The likelihood of a given galaxy hosting an AGN (L_bol>10^44 erg/s)
    increases by ~10-100 between a molecular gas mass of 10^8.7 Msun and 10^10.2
    Msun. Higher Eddington ratio AGN galaxies tend to have higher molecular gas
    masses and gas fractions. Higher column density AGN galaxies (Log NH>23.4) are
    associated with lower depletion timescales and may prefer hosts with more gas
    centrally concentrated in the bulge that may be more prone to quenching than
    galaxy wide molecular gas. The significant average link of host galaxy
    molecular gas supply to SMBH growth may naturally lead to the general
    correlations found between SMBHs and their host galaxies, such as the
    correlations between SMBH mass and bulge properties and the redshift evolution
    of star formation and SMBH growth.

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  • NuSTAR Non-detection of a Faint Active Galactic Nucleus in an Ultraluminous Infrared Galaxy with Kpc-scale Fast Wind

    Xiaoyang Chen, Kohei Ichikawa, Hirofumi Noda, Taiki Kawamuro, Toshihiro Kawaguchi, Yoshiki Toba, Masayuki Akiyama

    Astrophysical Journal Letters   905 ( 1 )  2020.12  [Refereed]

     View Summary

    © 2020. The American Astronomical Society. All rights reserved.. Large-scale outflows are generally considered to be possible evidence that active galactic nuclei (AGNs) can severely affect their host galaxies. Recently, an ultraluminous infrared galaxy (ULIRG) at z = 0.49, AKARI J0916248+073034, was found to have a galaxy-scale [O iii] λ 5007 outflow with one of the highest energy-ejection rates at z < 1.6. However, the central AGN activity estimated from its torus mid-infrared (MIR) radiation is weak relative to the luminous [O iii] emission. In this work we report the first NuSTAR hard X-ray follow-up of this ULIRG to constrain its current AGN luminosity. The intrinsic 2-10 keV luminosity shows a 90% upper limit of 3.0 × 1043 erg s-1 assuming Compton-thick obscuration (N H = 1.5 × 1024 cm-2), which is only 3.6% of the luminosity expected from the extinction-corrected [O iii] luminosity. Using the NuSTAR observation, we successfully identify that this ULIRG has a very extreme case of X-ray deficit among local ULIRGs. A possible scenario to explain the drastic decline in both the corona (X-ray) and torus (MIR) is that the primary radiation from the AGN accretion disk is currently in a fading status, as a consequence of a powerful nuclear wind suggested by powerful ionized outflow in a galaxy scale.

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  • Faint Quasars Live in the Same Number Density Environments as Lyman Break Galaxies at z similar to 4

    Hisakazu Uchiyama, Masayuki Akiyama, Jun Toshikawa, Nobunari Kashikawa, Roderik Overzier, Tohru Nagao, Kohei Ichikawa, Murilo Marinello, Masatoshi Imanishi, Masayuki Tanaka, Yoshiki Matsuoka, Yutaka Komiyama, Shogo Ishikawa, Masafusa Onoue, Mariko Kubo, Yuichi Harikane, Kei Ito, Shigeru Namiki, Yongming Liang

    ASTROPHYSICAL JOURNAL   905 ( 2 )  2020.12

     View Summary

    Characterizing high-z quasar environments is key to understanding the coevolution of quasars and the surrounding galaxies. To restrict their global picture, we statistically examine the g-dropout galaxy overdensity distribution around 570 faint quasar candidates at z similar to 4, based on the Hyper Suprime-Cam Subaru Strategic Program survey. We compare the overdensity significances of g-dropout galaxies around the quasars with those around g-dropout galaxies, and find no significant difference between their distributions. A total of 4 (22) out of the 570 faint quasars, 0.7-0.4+0.8, are found to be associated with the >4 sigma overdense regions within an angular separation of 1.8 (3.0) arcmin, which is the typical size of protoclusters at this epoch. This is similar to the fraction of g-dropout galaxies associated with the >4 sigma overdense regions. This result is consistent with our previous work in which 4 sigma overdense regions within 18 and 30 separations, respectively. Therefore, we suggest that the galaxy number densities around quasars are independent of their luminosity, and most quasars do not preferentially appear in the richest protocluster regions at z similar to 4. The lack of an apparent positive correlation between the quasars and the protoclusters implies that (i) the gas-rich major merger rate is relatively low in the protocluster regions, (ii) most high-z quasars may appear through secular processes, or (iii) some dust-obscured quasars exist in the protocluster regions.

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  • The Subaru HSC Galaxy Clustering with Photometric Redshift. I. Dark Halo Masses versus Baryonic Properties of Galaxies at 0.3 ≤ z ≤ 1.4

    Shogo Ishikawa, Nobunari Kashikawa, Masayuki Tanaka, Jean Coupon, Alexie Leauthaud, Jun Toshikawa, Kohei Ichikawa, Taira Oogi, Hisakazu Uchiyama, Yuu Niino, Atsushi J. Nishizawa

    Astrophysical Journal   904 ( 2 )  2020.12  [Refereed]

     View Summary

    © 2020. The American Astronomical Society. All rights reserved. We present the clustering properties of low-z (z ≤ 1.4) galaxies selected by the Hyper Suprime-Cam Subaru Strategic Program Wide layer over 145 deg2. The wide-field and multiwavelength observation yields 5,064,770 galaxies at 0.3 ≤ z ≤ 1.4 with photometric redshifts and physical properties. This enables the accurate measurement of angular correlation functions, and the subsequent halo occupation distribution (HOD) analysis allows us to identify the connection between baryonic and dark halo properties. The fraction of less-massive satellite galaxies at z ≲ 1 is found to be almost constant at ∼20%, but it gradually decreases beyond. However, the abundance of satellite galaxies at z > 1 is quite small even for less-massive galaxies due to the rarity of massive centrals at high-z. This decreasing trend is connected to the small satellite fraction of Lyman break galaxies at z > 3. The stellar-to-halo mass ratios at 0.3 ≤ z ≤ 1.4 are almost consistent with the predictions obtained using the latest empirical model; however, we identify small excesses from the theoretical model at the massive end. The pivot halo mass is found to be unchanged at at 0.3 ≤ z ≤ 1.4, and we systematically show that is a universal pivot halo mass up to z ∼ 5 that is derived using only the clustering/HOD analyses. Nevertheless, halo masses with peaked instantaneous baryon conversion efficiencies are much smaller than the pivot halo mass regardless of redshift, and the most efficient stellar-mass assembly is thought to be in progress in dark halos.

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  • Tracing the Coevolution Path of Supermassive Black Holes and Spheroids with AKARI-selected Ultraluminous IR Galaxies at Intermediate Redshifts

    Xiaoyang Chen, Masayuki Akiyama, Kohei Ichikawa, Hirofumi Noda, Yoshiki Toba, Issei Yamamura, Toshihiro Kawaguchi, Abdurro' Uf, Mitsuru Kokubo

    Astrophysical Journal   900 ( 1 )  2020.09  [Refereed]

     View Summary

    © 2020. The American Astronomical Society. All rights reserved.. We present the stellar population and ionized-gas outflow properties of ultraluminous IR galaxies (ULIRGs) at z = 0.1-1.0 that are selected from the AKARI far-IR all-sky survey. We construct a catalog of 1077 ULIRGs to examine feedback effects after major mergers. Of the 1077 ULIRGs, 202 are spectroscopically identified by SDSS and Subaru/FOCAS observations. Thanks to the deeper depth and higher resolution of AKARI compared to the previous Infrared Astronomical Satellite (IRAS) survey and reliable identification from the Wide-field Infrared Survey Explorer (WISE) mid-IR pointing, the sample is unique in identifying optically faint (i ∼ 20) IR-bright galaxies, which could be missed in previous surveys. A self-consistent spectrum and broadband spectral energy distribution (SED) decomposition method, which constrains stellar population properties in SED modeling based on spectral fitting results, has been employed for 149 ULIRGs whose optical continua are dominated by host galaxies. They are massive galaxies (Mstar ∼ 1011-1012 M⊙) associated with intense star formation activities (SFR ∼ 200-2000 M⊙ yr-1). The sample covers a range of active galactic nucleus (AGN) bolometric luminosity of 1010-1013 L⊙, and the outflow velocity measured from the [O iii] 5007 Å line shows a correlation with AGN luminosity. Eight galaxies show extremely fast outflows with velocity up to 1500-2000 km s-1. However, the coexistence of vigorous starbursts and strong outflows suggests the star formation has not been quenched during the ULIRG phase. By deriving the stellar mass and mass fraction of the young stellar population, we find no significant discrepancies between stellar properties of ULIRGs with weak and powerful AGNs. The results are not consistent with the merger-induced evolutionary scenario, which predicts that star formation-dominated ULIRGs will show smaller stellar masses and younger stellar populations compared to AGN-dominated ULIRGs.

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    8
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  • A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). III. Discovery of a z = 4.72 Radio Galaxy with the Lyman Break Technique

    Takuji Yamashita, Tohru Nagao, Hiroyuki Ikeda, Yoshiki Toba, Masaru Kajisawa, Yoshiaki Ono, Masayuki Tanaka, Masayuki Akiyama, Yuichi Harikane, Kohei Ichikawa, Toshihiro Kawaguchi, Taiki Kawamuro, Kotaro Kohno, Chien-Hsiu Lee, Kianhong Lee, Yoshiki Matsuoka, Mana Niida, Kazuyuki Ogura, Masafusa Onoue, Hisakazu Uchiyama

    The Astronomical Journal   160 ( 2 ) 60 - 60  2020.07  [Refereed]

     View Summary

    We report a discovery of a z = 4.72 radio galaxy, HSC J083913.17+011308.1, using the Lyman break technique with the Hyper Suprime-Cam Subaru Strategic Survey (HSC-SSP) catalog for Very Large Array Faint Images of the Radio Sky at Twenty centimeter radio sources. The number of known high-z radio galaxies (HzRGs) at z > 3 is quite small to constrain the evolution of HzRGs so far. The deep and wide-area optical survey by HSC-SSP enables us to apply the Lyman break technique to a large search for HzRGs. For an HzRG candidate among pre-selected r-band dropouts with a radio detection, a follow-up optical spectroscopy with the Gemini Multi-Object Spectrographs (GMOS)/Gemini has been performed. The obtained spectrum presents a clear Ly alpha emission line redshifted to z = 4.72. The spectral energy distribution fitting analysis with the rest-frame UV and optical photometries suggests the massive nature of this HzRG with logM*/M-circle dot = 11.4. The small equivalent width of Ly alpha and the moderately red UV colors indicate its dusty host galaxy, implying a chemically evolved and dusty system. The radio spectral index does not meet a criterion for an ultra-steep spectrum, alpha(325)(1400) of -1.1 and alpha(150)(1400) of -0.9, demonstrating that the HSC-SSP survey compensates for a subpopulation of HzRGs that are missed in surveys focusing on an ultra-steep spectral index.

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  • Application of an X-Ray Clumpy Torus Model (XCLUMPY) to 10 Obscured Active Galactic Nuclei Observed with Suzaku and NuSTAR

    Atsushi Tanimoto, Yoshihiro Ueda, Hirokazu Odaka, Shoji Ogawa, Satoshi Yamada, Toshihiro Kawaguchi, Kohei Ichikawa

    ASTROPHYSICAL JOURNAL   897 ( 1 )  2020.07  [Refereed]

     View Summary

    We apply XCLUMPY, an X-ray spectral model from a clumpy torus in an active galactic nucleus (AGN), to the broadband X-ray spectra of 10 obscured AGNs observed with both Suzaku and NuSTAR. The infrared spectra of these AGNs were analyzed by Ichikawa et al. with the CLUMPY code. Because XCLUMPY adopts the same clump distribution as that in the CLUMPY, we can directly compare the torus parameters obtained from the X-ray spectra and those from the infrared spectra. The torus angular widths determined from the infrared spectra (sigma(IR)) are systematically larger than those from the X-ray data (sigma(X)); the difference (sigma(IR) - sigma(X)) correlates with the inclination angle determined from the X-ray spectrum. These results can be explained by the contribution from dusty polar outflows to the observed infrared flux, which becomes more significant at higher inclinations (more edge-on views). The ratio of the hydrogen column density to the V-band extinction in the line-of-sight absorber shows a large scatter (similar or equal to 1 dex) around the Galactic value, suggesting that a significant fraction of AGNs have dust-rich circumnuclear environments.

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    5
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  • The BAT AGN Spectroscopic Survey. XVIII. Searching for Supermassive Black Hole Binaries in X-Rays

    Tingting Liu, Michael Koss, Laura Blecha, Claudio Ricci, Benny Trakhtenbrot, Richard Mushotzky, Fiona Harrison, Kohei Ichikawa, Darshan Kakkad, Kyuseok Oh, Meredith Powell, George C. Privon, Kevin Schawinski, T. Taro Shimizu, Krista Lynne Smith, Daniel Stern, Ezequiel Treister, C. Megan Urry

    ASTROPHYSICAL JOURNAL   896 ( 2 )  2020.06  [Refereed]

     View Summary

    Theory predicts that a supermassive black hole binary (SMBHB) could be observed as a luminous active galactic nucleus (AGN) that periodically varies on the order of its orbital timescale. In X-rays, periodic variations could be caused by mechanisms including relativistic Doppler boosting and shocks. Here we present the first systematic search for periodic AGNs using 941 hard X-ray light curves (14-195 keV) from the first 105 months of the Swift Burst Alert Telescope (BAT) survey (2004-2013). We do not find evidence for periodic AGNs in Swift-BAT, including the previously reported SMBHB candidate MCG+11-11-032. We find that the null detection is consistent with the combination of the upper-limit binary population in AGNs in our adopted model, their expected periodic variability amplitudes, and the BAT survey characteristics. We have also investigated the detectability of SMBHBs against normal AGN X-ray variability in the context of the extended ROentgen Survey with an Imaging Telescope Array (eROSITA) survey. Under our assumptions of a binary population and the periodic signals they produce, which have long periods of hundreds of days, up to 13% true periodic binaries can be robustly distinguished from normal variable AGNs with the ideal uniform sampling. However, we demonstrate that realistic eROSITA sampling is likely to be insensitive to long-period binaries because longer observing gaps reduce their detectability. In contrast, large observing gaps do not diminish the prospect of detecting binaries of short, few-day periods, as 19% can be successfully recovered, the vast majority of which can be identified by the first half of the survey.

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    11
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  • Universal Transition Diagram from Dormant to Actively Accreting Supermassive Black Holes

    Kohei Inayoshi, Kohei Ichikawa, Luis C. Ho

    ASTROPHYSICAL JOURNAL   894 ( 2 )  2020.05  [Refereed]

    Authorship:Corresponding author

     View Summary

    The vast majority of supermassive black holes (SMBHs) in the local universe exhibit levels of activity much lower than those expected from gas supplying rates onto the galactic nuclei, and only a small fraction of silent SMBHs can turn into active galactic nuclei. Revisiting observational data of very nearby SMBHs whose gravitational spheres of influence are spatially reached by the Chandra X-ray satellite, we find that the level of BH activity drastically increases from the quiescent phase when the inflow rate outside of the BH influence radius is higher than 0.1% of the Eddington accretion rate. We also show that the relation between the nuclear luminosity and gas accretion rate from the BH influence radius measured from X-ray observations is well described by the universal state transition of accreting SMBHs, as predicted by recent hydrodynamical simulations with radiative cooling and BH feedback. After the state transition, young massive stars should form naturally in the nucleus, as observed in the case of the nearest SMBH, Sagittarius A*, which is currently quiescent but was recently active.

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    11
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  • ALMA Polarimetry Measures Magnetically Aligned Dust Grains in the Torus of NGC 1068

    Enrique Lopez-Rodriguez, Almudena Alonso-Herrero, Santiago Garcia-Burillo, Michael S. Gordon, Kohei Ichikawa, Masatoshi Imanishi, Seiji Kameno, Nancy A. Levenson, Robert Nikutta, Chris Packham

    ASTROPHYSICAL JOURNAL   893 ( 1 )  2020.04  [Refereed]

     View Summary

    The obscuring structure surrounding active galactic nuclei (AGN) can be explained as a dust and gas flow cycle that fundamentally connects the AGN with their host galaxies. This structure is believed to be associated with dusty winds driven by radiation pressure. However, the role of magnetic fields, which are invoked in almost all models for accretion onto a supermassive black hole and outflows, has not been thoroughly studied. Here we report the first detection of polarized thermal emission by means of magnetically aligned dust grains in the dusty torus of NGC 1068 using ALMA Cycle 4 polarimetric dust continuum observations (007, 4.2 pc; 348.5 GHz, 860 mu m). The polarized torus has an asymmetric variation across the equatorial axis with a peak polarization of 3.7% 0.5% and position angle of 109 degrees 2 degrees (B-vector) at similar to 8 pc east from the core. We compute synthetic polarimetric observations of magnetically aligned dust grains assuming a toroidal magnetic field and homogeneous grain alignment. We conclude that the measured 860 mu m continuum polarization arises from magnetically aligned dust grains in an optically thin region of the torus. The asymmetric polarization across the equatorial axis of the torus arises from (1) an inhomogeneous optical depth and (2) a variation of the velocity dispersion, i.e., a variation of the magnetic field turbulence at subparsec scales, from the eastern to the western region of the torus. These observations and modeling constrain the torus properties beyond spectral energy distribution results. This study strongly supports that magnetic fields up to a few parsecs contribute to the accretion flow onto the active nuclei.

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  • Dust Destruction by Charging: A Possible Origin of Gray Extinction Curves of Active Galactic Nuclei

    Ryo Tazaki, Kohei Ichikawa, Mitsuru Kokubo

    ASTROPHYSICAL JOURNAL   892 ( 2 )  2020.04  [Refereed]

     View Summary

    Observed extinction curves of active galactic nuclei (AGNs) are significantly different from those observed in the Milky Way. The observations require preferential removal of small grains at the AGN environment; however, the physics for this remains unclear. In this paper, we propose that dust destruction by charging, or Coulomb explosion, may be responsible for AGN extinction curves. Harsh AGN radiation makes a dust grain highly charged through photoelectric emission, and grain fission via Coulomb explosion occurs when the electrostatic tensile stress of a charge grain exceeds its tensile strength. We show that Coulomb explosion can preferentially remove both small silicate and graphite grains and successfully reproduce both flat extinction curve and the absence of 2175 A bump.

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    17
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  • Dust Destruction by Drift-induced Sputtering in Active Galactic Nuclei

    Ryo Tazaki, Kohei Ichikawa

    ASTROPHYSICAL JOURNAL   892 ( 2 )  2020.04  [Refereed]

     View Summary

    Recent mid-infrared high spatial resolution observations have revealed that active galactic nuclei (AGNs) may host a polar dust region with the size of several pc, and such dust may be carried by radiation from the central engine. The polar dust emission often exhibits very weak or absence of the silicate 10 mu m emission feature. A possible explanation is that the polar dust is dominated by micron-sized large grains because these grains do not show the silicate feature, while it remains unclear how large grains are preferentially supplied to the polar region. Here, we propose a new scenario describing the prevalence of large grains at the polar region. We show that grains are accelerated to the hypersonic drift velocity by the radiation pressure from AGN, and the hypersonic drift results in dust destruction via kinetic sputtering. Sputtering destroys small grains faster than the large ones, and thus larger grains will be preferentially blown over longer distance. Although the hypersonic drift, or kinetic sputtering, tends to be suppressed for very small grains due to the Coulomb drag, they might also be disrupted by Coulomb explosion. Removal of small grains and/or survival of large grains may explain the lack of a silicate 10 mu m emission feature in polar dust emission.

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  • Obscuring Fraction of Active Galactic Nuclei Implied by Supernova and Radiative Feedbacks

    Nozomu Kawakatu, Keiichi Wada, Kohei Ichikawa

    ASTROPHYSICAL JOURNAL   889 ( 2 )  2020.02  [Refereed]

     View Summary

    We study the obscuring structure of circumnuclear disks (CNDs) by considering supernova (SN) feedbacks from nuclear starburst and the effect of anisotropic radiative pressure from active galactic nuclei (AGNs). We suppose that the mass accretion onto a central supermassive black hole (SMBH) is triggered by SN-driven turbulence within CNDs, and we explore how the structures of CNDs depend on the BH mass (M-BH) and AGN luminosity (L-AGN). We find that the obscuring fraction (f(obs)) peaks at similar to 10% of the Eddington luminosity (L-Edd), and its maximal value is f(obs) similar to 0.6 for less massive SMBHs (e.g., M-BH M<sub). This is because the scale height of CNDs is determined by the SN-driven accretion for a smaller L-AGN, while the dusty molecular gas in CNDs is blown away by the radiation pressure from AGNs beyond the critical luminosity. On the other hand, for massive SMBHs (e.g., M-BH > 10(8) M<sub), f(obs) is always smaller than 0.2, and it is almost independent of L-AGN because the scale height of CNDs is mainly controlled by the maximal star formation efficiency (C-*,C-max) in CNDs. In comparison with the obscuring fractions suggested from the mid-infrared observations of nearby AGNs, the SN plus radiative feedback model with C-*,C-max = 10(-7) yr(-1) reproduces the observations for M-BH = 10(8) M-circle dot well. We also find that the intense starburst or the existence of dust-free absorbers inside CNDs are necessary for explaining X-ray observations.

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  • BAT AGN Spectroscopic Survey - XIII. The nature of the most luminous obscured AGN in the low-redshift universe

    Bär, Rudolf E., Trakhtenbrot, Benny, Oh, Kyuseok, Koss, Michael J., Wong, O. Ivy, Ricci, Claudio, Schawinski, Kevin, Weigel, Anna K., Sartori, Lia F., Ichikawa, Kohei, Secrest, Nathan J., Stern, Daniel, Pacucci, Fabio, Mushotzky, Richard, Powell, Meredith C., Ricci, Federica, Sani, Eleonora, Smith, Krista L., Harrison, Fiona A., Lamperti, Isabella, Urry, C. Megan

    Monthly Notices of the Royal Astronomical Society   489 ( 3 ) 3073 - 3092  2019.11  [Refereed]

     View Summary

    We present a multiwavelength analysis of 28 of the most luminous low-redshift narrow-line, ultra-hard X-ray-selected active galactic nuclei (AGN) drawn from the 70-month Swift/BAT all-sky survey, with bolometric luminosities of log (L_bol /{erg s}^{-1}) ≳ 45.25. The broad goal of our study is to determine whether these objects have any distinctive properties, potentially setting them aside from lower luminosity obscured AGN in the local Universe. Our analysis relies on the first data release of the BAT AGN Spectroscopic Survey (BASS/DR1) and on dedicated observations with the VLT, Palomar, and Keck observatories. We find that the vast majority of our sources agree with commonly used AGN selection criteria which are based on emission line ratios and on mid-infrared colours. Our AGN are pre-dominantly hosted in massive galaxies (9.8 ≲ log (M*/M) ≲ 11.7); based on visual inspection of archival optical images, they appear to be mostly ellipticals. Otherwise, they do not have distinctive properties. Their radio luminosities, determined from publicly available survey data, show a large spread of almost four orders of magnitude - much broader than what is found for lower X-ray luminosity obscured AGN in BASS. Moreover, our sample shows no preferred combination of black hole masses (MBH) and/or Eddington ratio (λEdd), covering 7.5 ≲ log (MBH/M) ≲ 10.3 and 0.01 ≲ λEdd ≲ 1. Based on the distribution of our sources in the λEdd-NH plane, we conclude that our sample is consistent with a scenario where the amount of obscuring material along the line of sight is determined by radiation pressure exerted by the AGN on the dusty circumnuclear gas. <P />...

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  • WISE Discovery of Mid-infrared Variability in Massive Young Stellar Objects

    Uchiyama Mizuho, Ichikawa Kohei

    ASTROPHYSICAL JOURNAL   883 ( 1 ) 6 - 6  2019.09  [Refereed]

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  • NuSTAR Discovery of Dead Quasar Engine in Arp 187

    Kohei Ichikawa, Taiki Kawamuro, Megumi Shidatsu, Claudio Ricci, Hyun-Jin Bae, Kenta Matsuoka, Jaejin Shin, Yoshiki Toba, Junko Ueda, Yoshihiro Ueda

    The Astrophysical Journal Letters   883 ( 1 )  2019.09  [Refereed]

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  • A NuSTAR and XMM-Newton Study of the Two Most Actively Star-forming Green Pea Galaxies (SDSS J0749+3337 and SDSS J0822+2241)

    Taiki Kawamuro, Yoshihiro Ueda, Kohei Ichikawa, Masatoshi Imanishi, Takuma Izumi, Atsushi Tanimoto, Kenta Matsuoka

    ASTROPHYSICAL JOURNAL   881 ( 1 )  2019.08  [Refereed]

     View Summary

    We explore X-ray evidence for the presence of active galactic nuclei (AGNs) in the two most actively star-forming Green Pea galaxies (GPs), SDSS J0749+3337 and SDSS J0822+2241, which have star formation rates (SFRs) of 123 M-circle dot yr(-1) and 78 M-circle dot yr(-1), respectively. The GPs have red mid-infrared (MIR) spectral energy distributions and higher 22 mu m luminosities than expected from a proxy of the SFR (Ha luminosity), consistent with hosting AGNs with 2-10 keV luminosities of similar to 10(44) erg s(-1). We thus obtain and analyze the first hard (>10 keV) X-ray data observed with NuSTAR and archival XMM-Newton data below 10 keV. From the NuSTAR approximate to 20. ks data, however, we find no significant hard X-ray emission. By contrast, soft X-ray emission with 0.5-8 keV luminosities of approximate to 10(42) erg s(-1) is significantly detected in both targets, which can be explained only by star formation (SF). A possible reason for the lack of clear evidence is that a putative AGN torus absorbs most of the X-ray emission. Applying a smooth-density AGN torus model, we determine minimum hydrogen column densities along the equatorial plane (N-H(eq)) consistent with the nondetection. The results indicate N-H(eq) greater than or similar to 2 x 10(24) cm(-2) for SDSS J0749+3337 and N-H(eq) greater than or similar to 5 x 10(24) cm(-2) for SDSS J0822+2241. Therefore, the GPs may host such heavily obscured AGNs. Otherwise, no AGN exists and the MIR emission is ascribed to SF. Active SF in low-mass galaxies is indeed suggested to reproduce red MIR colors. This would imply that diagnostics based on MIR photometry data alone may misidentify such galaxies as AGNs.

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    3
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  • Transition of BH feeding from the quiescent regime into star-forming cold disc regime

    Kohei Inayoshi, Kohei Ichikawa, Jeremiah P. Ostriker, Rolf Kuiper

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY   486 ( 4 ) 5377 - 5390  2019.07  [Refereed]

     View Summary

    We study the properties of rotating accretion flows on to supermassive black holes (SMBIls) using, axisymmetric two-dimensional hydrodynamical simulations with radiative cooling, and B11 feedback. The simulations resolve the accretion dynamics of gas outside from the B11 influence radius through an inner accretion disc. For lower Bondi accretion rates in units of the Eddington rate ((111/B << 10 3 Ar./Edd). the BH feeding is suppressed due to turbulent motion by several orders of magnitude frotn the Bondi rate with outflows to the Bondi radius nearly balancing inflows. Thus, the radiative luminosity results in as low as 10 1u 107 LEdd, where LFdd is the Eddington luminosity. For higher rates of /111j >, 10 3 /1./Rid, the optically thin accreting gas cools via free free emission and forms a geometrically thin disc, which feeds the RH efficiently and increases the radiative luminosity to >JO 3 Lud. The transitional behaviour of accreting IiHs in galactic nuclei from radiatively inefficient phases to cold disc accretion naturally explains (1) the reason for the offset between the observed luminosities and theoretical predictions for nearby quiescent SMBHs, and (2) the conditions to fuel gas into the nuclear SWIM In addition, the cold disc formed in galactic nuclei tends to be gravitationally unstable and leads to star formation when the Bondi rate is as high as /114B > 10-2 M,-,-, yr-1. This is a plausible explanation of the correlation observed between star formation rates and BH feeding rates in Seyfert galaxies.

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    14
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  • A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). II. Physical Properties Derived from the SED Fitting with Optical, Infrared, and Radio Data

    Toba Yoshiki, Yamashita Takuji, Nagao Tohru, Wang Wei-Hao, Ueda Yoshihiro, Ichikawa Kohei, Kawaguchi Toshihiro, Akiyama Masayuki, Hsieh Bau-Ching, Kajisawa Masaru, Lee Chien-Hsiu, Matsuoka Yoshiki, Noboriguchi Akatoki, Onoue Masafusa, Schramm Malte, Tanaka Masayuki, Komiyama Yutaka

    ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES   243 ( 1 ) 15 - 15  2019.07  [Refereed]

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  • A kilometre-sized Kuiper belt object discovered by stellar occultation using amateur telescopes

    K. Arimatsu, K. Tsumura, F. Usui, Y. Shinnaka, K. Ichikawa, T. Ootsubo, T. Kotani, T. Wada, K. Nagase, J. Watanabe

    Nature Astronomy   3 ( 4 ) 301 - 306  2019.04  [Refereed]

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  • Discovery of a strong ionized-gas outflow in an AKARI-selected ultra-luminous infrared galaxy at z=0.5

    Chen Xiaoyang, Akiyama Masayuki, Noda Hirofumi, Abdurro'uf, Toba Yoshiki, Yamamura Issei, Kawaguchi Toshihiro, Kokubo Mitsuru, Ichikawa Kohei

    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN   71 ( 2 )  2019.04  [Refereed]

     View Summary

    In order to construct a sample of ultra-luminous infrared galaxies (ULIRGs; with infrared luminosity L-IR > 10(12) L-circle dot) at 0.5 < z < 1, we are conducting an optical follow-up program for bright 90 mu m far-infrared sources with a faint optical (i < 20 mag) counterpart selected in the AKARI Far-Infrared Surveyor (FIS) Bright Source catalog (Ver.2). AKARI-FIS-V2 J0916248+073034, identified as a ULIRG at z = 0.49 in the spectroscopic follow-up observation, indicates signatures of an extremely strong outflow in its emission line profiles. Its [O III] 5007 angstrom emission line shows a full width at half-maximum (FWHM) of 1830 kms(-1) and velocity shift of -770 kms(-1) relative to the stellar absorption lines. Furthermore, the low-ionization [OII] 3726 angstrom 3729 angstrom doublet also shows a large FWHM of 910 kms(-1) and velocity shift of -380 kms(-1). After the removal of an unresolved nuclear component, the long-slit spectroscopy 2D image possibly shows that the outflow extends to a radius of 4 kpc. The mass outflow and energy ejection rates are estimated to be 500M(circle dot) yr(-1) and 4 x 10(44) erg s(-1), respectively, which imply that the outflow is among the most powerful ones observed in ULIRGs and quasi-stellar objects at 0.3 < z < 1.6. The co-existence of the strong outflow and intense star formation (star formation rate of 990 M-circle dot yr(-1)) indicates that the feedback of the strong outflow has not severely affected the star-forming region of the galaxy.

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  • SOFIA/FORCAST resolves 30-40 mu m extended dust emission in nearby active galactic nuclei

    Fuller Lindsay, Lopez-Rodriguez Enrique, Packham Chris, Ichikawa Kohei, Togi Aditya, Alonso-Herrero Almudena, Ramos-Almeida Cristina, Diaz-Santos Tanio, Levenson N. A, Radomski James

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY   483 ( 3 ) 3404 - 3419  2019.03  [Refereed]

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  • Discovery of Dying Active Galactic Nucleus in Arp 187: Experience of Drastic Luminosity Decline within 104 yr

    Kohei Ichikawa, Junko Ueda, Hyun-Jin Bae, Taiki Kawamuro, Kenta Matsuoka, Yoshiki Toba, Megumi Shidatsu

    The Astrophysical Journal   870 ( 2 )  2019.01  [Refereed]

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  • BAT AGN Spectroscopic Survey. XI. The Covering Factor of Dust and Gas in Swift/BAT Active Galactic Nuclei

    Kohei Ichikawa, Claudio Ricci, Yoshihiro Ueda, Franz E. Bauer, Taiki Kawamuro, Michael J. Koss, Kyuseok Oh, David J. Rosario, T. Taro Shimizu, Marko Stalevski, Lindsay Fuller, Christopher Packham, Benny Trakhtenbrot

    The Astrophysical Journal   870 ( 1 )  2019.01  [Refereed]

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  • Gravitational Waves from Supermassive Black Hole Binaries in Ultraluminous Infrared Galaxies

    Kohei Inayoshi, Kohei Ichikawa, Zoltán Haiman

    The Astrophysical Journal Letters   863 ( 2 ) L36  2018.08  [Refereed]

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  • The origin of the mid-infrared nuclear polarization of active galactic nuclei

    {Lopez-Rodriguez}, E., {Alonso-Herrero}, A., {Diaz-Santos}, T., {Gonzalez-Martin}, O., {Ichikawa}, K., {Levenson}, N.~A., {Martinez-Paredes}, M., {Nikutta}, R., {Packham}, C., {Perlman}, E., {Ramos Almeida}, C., {Rodriguez-Espinosa}, J.~M., {Telesco}, C.~M.

    Monthly Notice of Royal Astronomical Society   478 ( 2 ) 2350 - 2358  2018.08  [Refereed]

    DOI

  • The Emission and Distribution of Dust of the Torus of NGC 1068

    Enrique Lopez-Rodriguez, Lindsay Fuller, Almudena Alonso-Herrero, Andreas Efstathiou, Kohei Ichikawa, Nancy A. Levenson, Chris Packham, James Radomski, Cristina Ramos Almeida, Dominic J. Benford, Marc Berthoud, Ryan Hamilton, Doyal Harper, Attila Kovávcs, Fabio P. Santos, J. Staguhn, Terry Herter

    Astrophysical Journal   859 ( 2 ) 99  2018.06  [Refereed]

     View Summary

    We present observations of NGC 1068 covering the 19.7-53.0 μm wavelength range using FORCAST and HAWC+ on board SOFIA. Using these observations, high-angular-resolution infrared (IR) and submillimeter observations, we find an observational turnover of the torus emission in the 30-40 μm wavelength range with a characteristic temperature of 70-100 K. This component is clearly different from the diffuse extended emission in the narrow line and star formation regions at 10-100 μm within the central 700 pc. We compute 2.2-432 μm 2D images using the best inferred clumpy torus model based on several nuclear spectral energy distribution (SED) coverages. We find that when 1-20 μm SED is used, the inferred result gives a small torus size (&lt
    4 pc radius) and a steep radial dust distribution. The computed torus using the 1-432 μm SED provides comparable torus sizes, pc radius, and morphology to the recently resolved 432 μm Atacama Large Millimeter Array observations. This result indicates that the 1-20 μm wavelength range is not able to probe the full extent of the torus. The characterization of the turnover emission of the torus using the 30-60 μm wavelength range is sensitive to the detection of cold dust in the torus. The morphology of the dust emission in our 2D image at 432 μm is spatially coincident with the cloud distribution, while the morphology of the emission in the 1-20 μm wavelength range shows an elongated morphology perpendicular to the cloud distribution. We find that our 2D clumpy torus image at 12 μm can produce comparable results to those observed using IR interferometry.

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  • The Key Science Drivers for MICHI: a thermal-infrared instrument for the TMT

    Chris Packham, Mitsuhiko Honda, Mark Chun, Itsuki Sakon, Matthew Richter, Yoshiko Okamoto, Hirokazu Kataza, Christian Marois, Michael Meyer, Manoj Puravankara, Jayne Birkby, Ian Crossfield, Thayne Currie, Thomas Greathouse, Gregory Herczeg, Kohei Ichikawa, Hanae Inami, Masatoshi Imanishi, Enrique Lopez-Rodriguez

    GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY VII   10702  2018

     View Summary

    With the imminent launch of the JWST, the field of thermal-infrared (TIR) astronomy will enjoy a revolution. It is easy to imagine that all areas of infrared (IR) astronomy will be greatly advanced, but perhaps impossible to conceive of the new vistas that will be opened. To allow both follow-up JWST observations and a continuance of work started on the ground-based 8m's, we continue to plan the science cases and instrument design for a TIR imager and spectrometer for early operation on the TMT. We present the current status of our science cases and the instrumentation plans, harnessing expertise across the TMT partnership. This instrument will be proposed by the MICHI team as a second-generation instrument in any upcoming calls for proposals.

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    6
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  • Luminous quasars do not live in the most overdense regions of galaxies at z ∼ 4

    Hisakazu Uchiyama, Jun Toshikawa, Nobunari Kashikawa, Roderik Overzier, Yi-Kuan Chiang, Murilo Marinello, Masayuki Tanaka, Yuu Niino, Shogo Ishikawa, Masafusa Onoue, Kohei Ichikawa, Masayuki Akiyama, Jean Coupon, Yuichi Harikane, Masatoshi Imanishi, Tadayuki Kodama, Yutaka Komiyama, Chien-Hsiu Lee, Yen-Ting Lin, Satoshi Miyazaki, Tohru Nagao, Atsushi J. Nishizawa, Yoshiaki Ono, Masami Ouchi, Shiang-Yu Wang

    Publications of the Astronomical Society of Japan   70  2018.01  [Refereed]

     View Summary

    We present the cross-correlation between 151 luminous quasars (MUV &lt
    -26) and 179 protocluster candidates at z ∼ 3.8, extracted from the Wide imaging survey (∼121 deg2) performed as part of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). We find that only two out of 151 quasars reside in regions that are more overdense compared to the average field at &gt
    4 σ. The distributions of the distances between quasars and the nearest protoclusters and the significance of the overdensity at the positions of quasars are statistically identical to those found for g-dropout galaxies, suggesting that quasars tend to reside in almost the same environment as star-forming galaxies at this redshift. Using stacking analysis, we find that the average density of g-dropout galaxies around quasars is slightly higher than that around g-dropout galaxies on 1.0-2.5 pMpc scales, while at &lt
    0.5 pMpc that around quasars tends to be lower. We also find that quasars with higher UV luminosity or with more massive black holes tend to avoid the most overdense regions, and that the quasar near-zone sizes are anti-correlated with overdensity. These findings are consistent with a scenario in which luminous quasars at z ∼ 4 reside in structures that are less massive than those expected for the progenitors of today's rich clusters of galaxies, and possibly that luminous quasarsmay be suppressing star formation in their close vicinity.

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    40
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  • BAT AGN Spectroscopic Survey. I. Spectral Measurements, Derived Quantities, and AGN Demographics

    Michael Koss, Benny Trakhtenbrot, Claudio Ricci, Isabella Lamperti, Kyuseok Oh, Simon Berney, Kevin Schawinski, Mislav Balokovic, Linda Baronchelli, D. Michael Crenshaw, Travis Fischer, Neil Gehrels, Fiona Harrison, Yasuhiro Hashimoto, Drew Hogg, Kohei Ichikawa, Nicola Masetti, Richard Mushotzky, Lia Sartori, Daniel Stern, Ezequiel Treister, Yoshihiro Ueda, Sylvain Veilleux, Lisa Winter

    ASTROPHYSICAL JOURNAL   850 ( 1 )  2017.11  [Refereed]

     View Summary

    We present the first catalog and data release of the Swift-BAT AGN Spectroscopic Survey. We analyze optical spectra of the majority of the detected AGNs (77%, 642/836)based on their 14-195 keV emission in the 70-month Swift-BAT all-sky catalog. This includes redshift determination, absorption and emission-line measurements, and black hole mass and accretion rate estimates for the majority of obscured and unobscured AGNs (74%, 473/642), with 340 measured for the first time. With-90% of sources at z &lt; 0.2, the survey represents a significant advance in the census of hard X-ray-selected AGNs in the local universe. In this first catalog paper, we describe the spectroscopic observations and data sets, and our initial spectral analysis. The FWHMs of the emission lines show broad agreement with the X-ray obscuration (similar to 94%), such that Sy 1-1.8 have N-H &lt; 10(21.9) cm(-2), and Seyfert 2 have N-H &gt; 10(21.9) cm(-2). Seyfert 1.9, however, show a range of column densities. Compared to narrow-line AGNs in the SDSS, the X-ray-selected AGNs have a larger fraction of dusty host galaxies (H alpha/H beta &gt; 5), suggesting that these types of AGN are missed in optical surveys. Using the [O III] lambda 5007/H beta and [N lambda 6583/H alpha emission-line diagnostic, about half of the sources are classified as Seyferts similar to 15% reside in dusty galaxies that lack an H beta detection, but for which the upper limits on line emission imply either a Seyfert or LINER similar to 15% are in galaxies with weak or no emission lines despite high-quality spectra, and a few percent each are LINERS, composite galaxies, H II regions, or in known beamed AGNs.

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  • NuSTAR Hard X-Ray Data and Gemini 3D Spectra Reveal Powerful AGN and Outflow Histories in Two Low-redshift Ly alpha Blobs

    Taiki Kawamuro, Mischa Schirmer, James E. H. Turner, Rebecca L. Davies, Kohei Ichikawa

    ASTROPHYSICAL JOURNAL   848 ( 1 ) 42  2017.10  [Refereed]

     View Summary

    We have shown that Ly alpha blobs (LABs) may still exist even at z similar to 0.3, about seven billion years later than most other LABs known (Shirmer et al.). Their luminous Lya and [O III] emitters at z similar to 0.3 offer new insights into the ionization mechanism. This paper focuses on the two X-ray brightest LABs at z similar to 0.3, SDSS J0113+0106 (J0113) and SDSS J1155-0147 (J1155), comparable in size and luminosity to "B1," one of the best-studied LABs at z greater than or similar to 2. Our NuSTAR hard X-ray (3-30 keV) observations reveal powerful active galactic nuclei (AGN) with L2-10 keV = (0.53) x 10(44) erg s(-1). J0113 also faded by a factor of similar to 5 between 2014 and 2016, emphasizing that variable AGN may cause apparent ionization deficits in LABs. Joint spectral analyses including Chandra data constrain column densities of N-H = 5.1(-3.3)(+10) = 3.1(23) cm(-2) (J0113) and N-H = 6.0(-1.1)(+1.4) 10(22) cm(-2) (J1155). J0113 is likely buried in a torus with a narrow ionization cone, but ionizing radiation is also leaking in other directions, as revealed by our Gemini/GMOS 3D spectroscopy. The latter shows a bipolar outflow over 10 kpc, with a peculiar velocity profile that is best explained by AGN flickering. X-ray analysis of J1155 reveals a weakly absorbed AGN that may ionize over a wide solid angle, consistent with our 3D spectra. Extinction-corrected [O III] logluminosities are high, similar to 43.6. The velocity dispersions are low, similar to 100-150 km s(-1), even at the AGN positions. We argue that this is a combination of high extinction hiding the turbulent gas and previous outflows that have cleared the escape paths for their successors.

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    8
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  • Organized Autotelescopes for Serendipitous Event Survey (OASES): Design and performance

    Ko Arimatsu, Kohji Tsumura, Kohei Ichikawa, Fumihiko Usui, Takafumi Ootsubo, Takayuki Kotani, Yuki Sarugaku, Takehiko Wada, Koichi Nagase, Jun-ichi Watanabe

    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN   69 ( 4 )  2017.08  [Refereed]

     View Summary

    Organized Autotelescopes for Serendipitous Event Survey (OASES) is an optical observation project that aims to detect and investigate stellar occultation events by kilometer-sized trans-Neptunian objects (TNOs). In this project, multiple low-cost observation systems for wide-field and high-speed photometry were developed in order to detect rare and short-timescale stellar occultation events. The observation system consists of commercial off-the-shelf 0.28m aperture f/1.58 optics providing a 2.degrees 3 x 1.degrees 8 field of view. A commercial CMOS camera is coupled to the optics to obtain full-frame imaging with a frame rate greater than 10 Hz. As of 2016 September, this project exploits two observation systems, which are installed on Miyako Island, Okinawa, Japan. Recent improvements in CMOS technology in terms of high-speed imaging and low readout noise mean that the observation systems are capable of monitoring similar to 2000 stars in the Galactic plane simultaneously with magnitudes down to V similar to 13.0, providing similar to 20% photometric precision in light curves with a sampling cadence of 15.4 Hz. This number of monitored stars is larger than for any other existing instruments for coordinated occultation surveys. In addition, a precise time synchronization method needed for simultaneous occultation detection is developed using faint meteors. The two OASES observation systems are executing coordinated monitoring observations of a dense stellar field in order to detect occultations by kilometer-sized TNOs for the first time.

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    14
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  • Cooling Timescale of Dust Tori in Dying Active Galactic Nuclei

    Kohei Ichikawa, Ryo Tazaki

    ASTROPHYSICAL JOURNAL   844 ( 1 ) 21  2017.07  [Refereed]

     View Summary

    We estimate the dust torus cooling timescale once the active galactic nucleus (AGN) is quenched. In a clumpy torus system, once the incoming photons are suppressed, the cooling timescale of one clump from T-dust = 1000 K to several 10 K is less than 10 years, indicating that the dust torus cooling time is mainly governed by the light crossing time of the torus from the central engine. After considering the light crossing time of the torus, the AGN torus emission at 12 mu m becomes over two orders of magnitude fainter within 100 years after the quenching. We also propose that those "dying" AGNs could be found using the AGN indicators with a different physical scale R such as 12 mu m band luminosity tracing AGN torus (R similar to 10 pc) and the optical [O III]lambda 5007 emission line tracing narrow line regions (R = 10(2-4) pc).

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    14
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  • The dusty tori of nearby QSOs as constrained by high-resolution mid-IR observations

    M. Martinez-Paredes, I. Aretxaga, A. Alonso-Herrero, O. Gonzalez-Martin, E. Lopez-Rodriguez, C. Ramos Almeida, A. Asensio Ramos, T. Diaz Santos, M. Elitzur, P. Esquej, A. Hernan-Caballero, K. Ichikawa, R. Nikutta, C. Packham, M. Pereira-Santaella, C. Telesco

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY   468 ( 1 ) 2 - 46  2017.06  [Refereed]

     View Summary

    We present mid-infrared (MIR; 7.5-13.5 mu m) imaging and spectroscopy observations obtained with the CanariCam (CC) instrument on the 10.4-m Gran Telescopio CANARIAS for a sample of 20 nearby, MIR bright and X-ray luminous quasi-stellar objects (QSOs). We find that for the majority of QSOs the MIR emission is unresolved at angular scales-0.3 arcsec, corresponding to physical scales &lt;= 600 pc. We find that the higher-spatial resolution CC spectra have similar shapes to those obtained with Spitzer/ IRS, and hence we can assume that the spectra are not heavily contaminated by extended emission in the host galaxy. We thus take advantage of the higher signal-to-noise ratio Spitzer/IRS spectra, as a fair representation of the nuclear emission, to decompose it into a combination of active galactic nuclei (AGN), polycyclic aromatic hydrocarbon (PAH) and stellar components. In most cases, the AGN is the dominant component, with a median contribution of 85 per cent of the continuum light at MIR (5-15 mu m) within the IRS slit. This IR AGN emission is well reproduced by CLUMPY torus models. We find evidence for significant differences in the parameters that describe the dusty tori of QSOs when compared with the same parameters of Seyfert 1 and 2 nuclei. In particular, we find a lower number of clouds (N-0 &lt;= 12), steeper radial distribution of clouds (q -1.5-3.0) and clouds that are less optically thick (iota(V) &lt;= 100) than in Seyfert 1, which could be attributed to dusty structures that have been partially evaporated and piled up by the higher radiation field in QSOs. We find that the combination of the angular width sigma(torus), viewing angle i, and number of clouds along the equatorial line, N-0, produces large escape probabilities (P-esc &gt; 2 per cent) and low geometrical covering factors (f(2) &lt;= 0.6), as expected for AGN with broad lines in their optical spectra.

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    23
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  • Quenching of Supermassive Black Hole Growth around the Apparent Maximum Mass

    Kohei Ichikawa, Kohei Inayoshi

    ASTROPHYSICAL JOURNAL LETTERS   840 ( 1 )  2017.05  [Refereed]

     View Summary

    Recent quasar surveys have revealed that supermassive black holes (SMBHs) rarely exceed a mass of MBH similar to a few x 10(10) M-circle dot during the entire cosmic history. It has been argued that quenching of the BH growth is caused by a transition of a nuclear accretion disk into an advection-dominated accretion flow, with which strong outflows and/or jets are likely to be associated. We investigate the relationship between the maximum mass of SMBHs and the radio-loudness of quasars with a well-defined sample of similar to 10(5) quasars at a redshift range of 0 &lt; z &lt; 2, obtained from the Sloan Digital Sky Surveys DR7 catalog. We find that the number fraction of the radio-loud (RL) quasars increases above a threshold of MBH similar or equal to 2. x 10(9) M-circle dot, independent of their redshifts. Moreover, the number fraction of RL quasars with lower Eddington ratios (out of all RL quasars), indicating lower accretion rates, increases above the critical BH mass. These observational trends can be natural consequences of the proposed scenario of suppressing BH growth around the apparent maximum mass of 10(10) M-circle dot. The ongoing VLA Sky Survey in radio will allow us to estimate of the exact number fraction of RL quasars more precisely, which gives further insight into the quenching processes for BH growth.

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    14
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  • The Galaxy-Halo Connection in High-redshift Universe: Details and Evolution of Stellar-to-halo Mass Ratios of Lyman Break Galaxies on CFHTLS Deep Fields

    Shogo Ishikawa, Nobunari Kashikawa, Jun Toshikawa, Masayuki Tanaka, Takashi Hamana, Yuu Niino, Kohei Ichikawa, Hisakazu Uchiyama

    ASTROPHYSICAL JOURNAL   841 ( 1 )  2017.05  [Refereed]

     View Summary

    We present the results of clustering analyses of Lyman break galaxies (LBGs) at z similar to 3, 4, and 5 using the final data release of the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). Deep- and wide-field images of the CFHTLS Deep Survey enable us to obtain sufficiently accurate two-point angular correlation functions to apply a halo occupation distribution analysis. The mean halo masses, calculated as &lt; M-h &gt; = 10(11.7)-10(12.8) h(-1) M-circle dot, increase with the stellar-mass limit of LBGs. The threshold halo mass to have a central galaxy, M-min, follows the same increasing trend as the low-z results, whereas the threshold halo mass to have a satellite galaxy, M-1, shows higher values at z = 3-5 than z = 0.5-1.5, over the entire stellar mass range. Satellite fractions of dropout galaxies, even at less massive halos, are found to drop sharply, from z = 2 down to less than 0.04, at z = 3-5. These results suggest that satellite galaxies form inefficiently within dark halos at z = 3-5, even for less massive satellites with M-star &lt; 10(10) M-circle dot. We compute stellar-to-halo mass ratios (SHMRs) assuming a main sequence of galaxies, which is found to provide SHMRs consistent with those derived from a spectral energy distribution fitting method. The observed SHMRs are in good agreement with model predictions based on the abundance-matching method, within 1 sigma confidence intervals. We derive observationally, for the first time, M-h(pivot), which is the halo mass at a peak in the star-formation efficiency, at 3 &lt; z &lt; 5, and it shows a small increasing trend with cosmic time at z &gt; 3. In addition, M-h(pivot) and its normalization are found to be almost unchanged during 0 &lt; z &lt; 5. Our study provides observational evidence that galaxy formation is ubiquitously most efficient near a halo mass of M-h similar to 10(12) M-circle dot over cosmic time.

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    21
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  • Infrared polarimetry of Mrk 231: scattering off hot dust grains in the central core

    E. Lopez-Rodriguez, C. Packham, T. J. Jones, R. Siebenmorgen, P. F. Roche, N. A. Levenson, A. Alonso-Herrero, E. Perlman, K. Ichikawa, C. Ramos Almeida, O. Gonzalez-Martin, R. Nikutta, M. Martinez-Paredez, D. Shenoy, M. S. Gordon, C. M. Telesco

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY   464 ( 2 ) 1762 - 1770  2017.01  [Refereed]

     View Summary

    We present high-angular (0.17-0.35 arcsec) resolution imaging polarimetric observations of Mrk 231 in the 3.1 mu m filter using MMT-Pol on the 6.5-m MMT, and in the 8.7, 10.3, and 11.6 mu m filters using CanariCam on the 10.4-m Gran Telescopio CANARIAS. In combination with already published observations, we compile the 1-12 mu m total and polarized nuclear spectral energy distribution (SED). The total flux SED in the central 400 pc is explained as the combination of (1) a hot (731 +/- 4 K) dusty structure, directly irradiated by the central engine, which is at 1.6 +/- 0.1 pc away and attributed to be in the pc-scale polar region, (2) an optically-thick, smooth and disc-like dusty structure ('torus') with an inclination of 48 degrees +/- 23 degrees surrounding the central engine, and (3) an extinguished (A(V) = 36 +/- 5 mag) starburst component. The polarized SED decreases from 0.77 +/- 0.14 per cent at 1.2 mu m to 0.31 +/- 0.15 per cent at 11.6 mu m and follows a power-law function, lambda(similar to 0.57). The polarization angle remains constant (similar to 108 degrees) in the 1-12 mu m wavelength range. The dominant polarization mechanism is explained as scattering-off hot dust grains in the pc-scale polar regions.

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    7
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  • THE COMPLETE INFRARED VIEW OF ACTIVE GALACTIC NUCLEI FROM THE 70MONTH SWIFT/BAT CATALOG

    Kohei Ichikawa, Claudio Ricci, Yoshihiro Ueda, Kenta Matsuoka, Yoshiki Toba, Taiki Kawamuro, Benny Trakhtenbrot, Michael J. Koss

    ASTROPHYSICAL JOURNAL   835 ( 1 )  2017.01  [Refereed]

     View Summary

    We systematically investigate the near-to far-infrared (FIR) photometric properties of a nearly complete sample of local active galactic nuclei (AGNs) detected in the Swift/Burst Alert Telescope (BAT) all-sky ultra-hard X-ray (14-195 keV) survey. Out of 606 non-blazar AGNs in the Swift/BAT 70 month catalog at high galactic latitudes of vertical bar b vertical bar &gt; 10 degrees, we obtain IR photometric data of 604 objects by cross-matching the AGN positions with catalogs from the WISE, AKARI, IRAS, and Herschel infrared observatories. We find a good correlation between the ultra-hard X-ray and mid-IR luminosities over five orders of magnitude (41&lt; log L14-195 &lt; 46). Informed by previous measurements of the intrinsic spectral energy distribution of AGNs, we find FIR pure-AGN candidates whose FIR emission is thought to be AGN-dominated with low star-formation activity. We demonstrate that the dust covering factor decreases with the bolometric AGN luminosity, confirming the luminosity-dependent unified scheme. We also show that the completeness of the WISE color-color cut in selecting Swift/BAT AGNs increases strongly with 14-195 keV luminosity.

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    74
    Citation
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  • The nuclear and extended mid-infrared emission of Seyfert galaxies

    I. Garcia-Bernete, C. Ramos Almeida, J. A. Acosta-Pulido, A. Alonso-Herrero, O. Gonzalez-Martin, A. Hernan-Caballero, M. Pereira-Santaella, N. A. Levenson, C. Packham, E. S. Perlman, K. Ichikawa, P. Esquej, T. Diaz-Santos

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY   463 ( 4 ) 3531 - 3555  2016.12  [Refereed]

     View Summary

    We present subarcsecond resolution mid-infrared (MIR) images obtained with 8-10 m-class ground-based telescopes of a complete volume-limited (D-L &lt; 40 Mpc) sample of 24 Seyfert galaxies selected from the Swift/Burst Alert Telescope nine month catalogue. We use those MIR images to study the nuclear and circumnuclear emission of the galaxies. Using different methods to classify the MIR morphologies on scales of similar to 400 pc, we find that the majority of the galaxies (75-83 per cent) are extended or possibly extended and 17-25 per cent are point-like. This extended emission is compact and it has low surface brightness compared with the nuclear emission, and it represents, on average, similar to 30 per cent of the total MIR emission of the galaxies in the sample. We find that the galaxies whose circumnuclear MIR emission is dominated by star formation (SF) show more extended emission (650 +/- 700 pc) than active galactic nuclei (AGN)-dominated systems (300 +/- 100 pc). In general, the galaxies with point-like MIR morphologies are face-on or moderately inclined (b/a similar to 0.4-1.0), and we do not find significant differences between the morphologies of Sy1 and Sy2. We used the nuclear and circumnuclear fluxes to investigate their correlation with different AGN and SF activity indicators. We find that the nuclear MIR emission (the inner similar to 70 pc) is strongly correlated with the X-ray emission (the harder the X-rays the better the correlation) and with the [O IV] lambda 25.89 mu m emission line, indicating that it is AGN-dominated. We find the same results, although with more scatter, for the circumnuclear emission, which indicates that the AGN dominates the MIR emission in the inner similar to 400 pc of the galaxies, with some contribution from SF.

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    23
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  • The complex evolutionary paths of local infrared bright galaxies: a high-angular resolution mid-infrared view

    A. Alonso-Herrero, R. Poulton, P. F. Roche, A. Hernan-Caballero, I. Aretxaga, M. Martinez-Paredes, C. Ramos Almeida, M. Pereira-Santaella, T. Diaz-Santos, N. A. Levenson, C. Packham, L. Colina, P. Esquej, O. Gonzalez-Martin, K. Ichikawa, M. Imanishi, J. M. Rodriguez Espinosa, C. Telesco

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY   463 ( 3 ) 2405 - 2424  2016.12  [Refereed]

     View Summary

    We investigate the evolutionary connection between local infrared (IR)-bright galaxies (log L-IR &gt;= 11.4 L-circle dot) and quasars. We use high-angular resolution (similar to 0.3-0.4 arcsec similar to few hundred parsecs) 8-13 mu m ground-based spectroscopy to disentangle the active galactic nuclei (AGN) mid-IR properties from those of star formation. The comparison between the nuclear 11.3 mu m polycyclic aromatic hydrocarbon feature emission and that measured with Spitzer/Spitzer Infrared Spectrograph indicates that the star formation is extended over a few kpc in the IR-bright galaxies. The AGN contribution to the total IR luminosity of IR-bright galaxies is lower than in quasars. Although the dust distribution is predicted to change as IR-bright galaxies evolve to IR-bright quasars and then to optical quasars, we show that the AGN mid-IR emission of all the quasars in our sample is not significantly different. In contrast, the nuclear emission of IR-bright galaxies with low AGN contributions appears more heavily embedded in dust although there is no clear trend with the interaction stage or projected nuclear separation. This suggests that the changes in the distribution of the nuclear obscuring material may be taking place rapidly and at different interaction stages washing out the evidence of an evolutionary path. When compared to normal AGN, the nuclear star formation activity of quasars appears to be dimming, whereas it is enhanced in some IR-bright nuclei, suggesting that the latter are in an earlier star formation-dominated phase.

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    15
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  • Investigating the dusty torus of Seyfert galaxies using SOFIA/FORCAST photometry

    L. Fuller, E. Lopez-Rodriguez, C. Packham, C. Ramos-Almeida, A. Alonso-Herrero, N. A. Levenson, J. Radomski, K. Ichikawa, I. Garcia-Bernete, O. Gonzalez-Martin, T. Diaz-Santos, M. Martinez-Paredes

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY   462 ( 3 ) 2618 - 2630  2016.11  [Refereed]

     View Summary

    We present 31.5 mu m imaging photometry of 11 nearby Seyfert galaxies observed from the Stratospheric Observatory For Infrared Astronomy (SOFIA) using the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST). We tentatively detect extended 31 mu m emission for the first time in our sample. In combination with this new data set, subarcsecond resolution 1-18 mu m imaging and 7.5-13 mu m spectroscopic observations were used to compute the nuclear spectral energy distribution (SED) of each galaxy. We found that the turnover of the torus emission does not occur at wavelengths &lt;= 31.5 mu m, which we interpret as a lower-limit for the wavelength of peak emission. We used CLUMPY torus models to fit the nuclear infrared (IR) SED and infer trends in the physical parameters of the AGN torus for the galaxies in the sample. Including the 31.5 mu m nuclear flux in the SED (1) reduces the number of clumpy torus models compatible with the data, and (2) modifies the model output for the outer radial extent of the torus for 10 of the 11 objects. Specifically, six (60 per cent) objects show a decrease in radial extent while four (40 per cent) show an increase. We find torus outer radii ranging from &lt;1 to 8.4 pc.

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    25
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  • The nuclear and integrated far-infrared emission of nearby Seyfert galaxies

    J. Garcia-Gonzalez, A. Alonso-Herrero, A. Hernan-Caballero, M. Pereira-Santaella, C. Ramos-Almeida, J. A. Acosta-Pulido, T. Diaz-Santos, P. Esquej, O. Gonzalez-Martin, K. Ichikawa, E. Lopez-Rodriguez, M. Povic, P. F. Roche, M. Sanchez-Portal

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY   458 ( 4 ) 4512 - 4529  2016.06  [Refereed]

     View Summary

    We present far-infrared (FIR) 70-500 mu m imaging observations obtained with Herschel/Photodetector Array Camera (PACS) and Spectral and Photometric Imaging REceiver (SPIRE) of 33 nearby (median distance of 30 Mpc) Seyfert galaxies from the Revised Shapley-Ames (RSA) catalogue. We obtain the FIR nuclear (r = 1 kpc and r = 2 kpc) and integrated spectral energy distributions (SEDs). We estimate the unresolved nuclear emission at 70 mu m and we fit the nuclear and integrated FIR SEDs with a grey body model. We find that the integrated FIR emission of the RSA Seyferts in our sample is dominated by emission from the host galaxy, with dust properties similar to those of normal galaxies (non-AGN). We use four criteria to select galaxies whose nuclear 70 mu m emission has a significant AGN contribution: (1) elevated 70/160 mu m flux ratios, (2) spatially resolved, high dust temperature gradient, (3) 70 mu m excess emission with respect to the fit of the FIR SEDs with a grey body, and (4) excess of nuclear SFR obtained from 70 mu m over SFR from mid-infrared indicators. 16 galaxies (48 per cent of the initial sample) satisfy at least one of these conditions, whereas 10 satisfy half or more. After careful examination of these, we select six bona fide candidates (18 per cent of the initial sample) and estimate that similar to 40-70 per cent of their nuclear (r = 1-2 kpc) 70 mu m emission is contributed by dust heated by the AGN.

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  • Signs of active galactic nucleus quenching in a merger remnant with radio jets

    Kohei Ichikawa, Junko Ueda, Megumi Shidatsu, Taiki Kawamuro, Kenta Matsuoka

    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN   68 ( 1 )  2016.02  [Refereed]

     View Summary

    We investigate optical, infrared, and radio active galactic nucleus (AGN) signs in the merger remnant Arp 187, which hosts luminous jets launched in the order of 10(5) yr ago but whose present-day AGN activity is still unknown. We find AGN signs from the optical Baldwin-Phillips-Telervich diagram and infrared [O IV] 25.89 mu m line, originating from the narrow line regions of AGN. On the other hand, Spitzer/IRS show host galaxy dominated spectra, suggesting that the thermal emission from the AGN torus is considerably small or already diminished. Combining the black holemass, the upper limit of radio luminosity of the core, and the fundamental plane of the black hole enables us to estimate X-ray luminosity, which gives &lt; 10(40) erg s(-1). Those results suggest that the AGN activity of Arp 187 has already been quenched, but the narrow line region is still alive owing to the time delay of emission from the past AGN activity.

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    7
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  • BAT AGN spectroscopic survey-II. X-ray emission and high-ionization optical emission lines

    Simon Berney, Michael Koss, Benny Trakhtenbrot, Claudio Ricci, Isabella Lamperti, Kevin Schawinski, Mislav Balokovic, D. Michael Crenshaw, Travis Fischer, Neil Gehrels, Fiona Harrison, Yasuhiro Hashimoto, Kohei Ichikawa, Richard Mushotzky, Kyuseok Oh, Daniel Stern, Ezequiel Treister, Yoshihiro Ueda, Sylvain Veilleux, Lisa Winter

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY   454 ( 4 ) 3622 - 3634  2015.12  [Refereed]

     View Summary

    We investigate the relationship between X-ray and optical line emission in 340 nearby (z similar or equal to 0.04) AGN selected above 10 keV using Swift BAT. We find a weak correlation between the extinction corrected [O III] and hard X-ray luminosity (L-[O III](int) alpha L14-195) with a large scatter (R-Pear = 0.64, sigma = 0.62 dex) and a similarly large scatter with the intrinsic 2-10 keV to [O III] luminosities (R-Pear = 0.63, sigma = 0.63 dex). Correlations of the hard X-ray fluxes with the fluxes of high-ionization narrow lines ([O III], He II, [Ne III] and [Ne V]) are not significantly better than with the low-ionization lines (H alpha, [S II]). Factors like obscuration or physical slit size are not found to be a significant part of the large scatter. In contrast, the optical emission lines show much better correlations with each other (sigma = 0.3 dex) than with the X-ray flux. The inherent large scatter questions the common usage of narrow emission lines as AGN bolometric luminosity indicators and suggests that other issues such as geometrical differences in the scattering of the ionized gas or long-term AGN variability are important.

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    57
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  • [O III] lambda 5007 AND X-RAY PROPERTIES OF A COMPLETE SAMPLE OF HARD X-RAY SELECTED AGNS IN THE LOCAL UNIVERSE

    Y. Ueda, Y. Hashimoto, K. Ichikawa, Y. Ishino, A. Y. Kniazev, P. Vaeisaenen, C. Ricci, S. Berney, P. Gandhi, M. Koss, R. Mushotzky, Y. Terashima, B. Trakhtenbrot, M. Crenshaw

    ASTROPHYSICAL JOURNAL   815 ( 1 ) 1  2015.12  [Refereed]

     View Summary

    We study the correlation between the [O III]..5007 and X-ray luminosities of local active galactic nuclei (AGNs), using a complete, hard X-ray (&gt;10 keV) selected sample in the Swift/BAT 9-month catalog. From our optical spectroscopic observations at the South African Astronomical Observatory and the literature, a catalog of [O III]..5007 line flux for all 103 AGNs at Galactic latitudes of vertical bar b vertical bar &gt; 15 degrees is compiled. Significant correlations with intrinsic X-ray luminosity (L-X) are found for both observed (L[O III]) and extinction-corrected (L-[O (cor)(III])) luminosities, separately for X-ray unabsorbed and absorbed AGNs. We obtain the regression form of L-[O III] alpha L-2-10keV(1.18 +/- 0.07) and L-[O III](cor) alpha L-2-10keV(1.16 +/- 0.09) from the whole sample. The absorbed AGNs with low (&lt;0.5%) scattering fractions in soft X-rays show on average smaller L-[OIII]/L-X and L-[OIII](cor)/L-X ratios than the other absorbed AGNs, while those in edge-on host galaxies do not. These results suggest that a significant fraction of this population is buried in tori with small opening angles. By using these L-[OIII] versus L-X correlations, the X-ray luminosity function (LF) of local AGNs (including Compton-thick AGNs) in a standard population synthesis model gives much better agreement with the [O III] lambda 5007 LF derived from the Sloan Digital Sky Survey than previously reported. This confirms that hard X-ray observations are a very powerful tool to find AGNs with high completeness.

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    56
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  • THE DIFFERENCES IN THE TORUS GEOMETRY BETWEEN HIDDEN AND NON-HIDDEN BROAD LINE ACTIVE GALACTIC NUCLEI

    Kohei Ichikawa, Christopher Packham, Cristina Ramos Almeida, Andres Asensio Ramos, Almudena Alonso-Herrero, Omaira Gonzalez-Martin, Enrique Lopez-Rodriguez, Yoshihiro Ueda, Tanio Diaz-Santos, Moshe Elitzur, Sebastian F. Honig, Masatoshi Imanishi, Nancy A. Levenson, Rachel E. Mason, Eric S. Perlman, Crystal D. Alsip

    ASTROPHYSICAL JOURNAL   803 ( 2 ) 57  2015.04  [Refereed]

     View Summary

    We present results from the fitting of infrared (IR) spectral energy distributions of 21 active galactic nuclei (AGNs) with clumpy torus models. We compiled high spatial resolution (similar to 0.3-0.7 arcsec) mid-IR (MIR) N-band spectroscopy, Q-band imaging, and nuclear near-and MIR photometry from the literature. Combining these nuclear near-and MIR observations, far-IR photometry, and clumpy torus models enables us to put constraints on the torus properties and geometry. We divide the sample into three types according to the broad line region (BLR) properties: type-1s, type-2s with scattered or hidden broad line region (HBLR) previously observed, and type-2s without any published HBLR signature (NHBLR). Comparing the torus model parameters gives us the first quantitative torus geometrical view for each subgroup. We find that NHBLR AGNs have smaller torus opening angles and larger covering factors than HBLR AGNs. This suggests that the chance to observe scattered (polarized) flux from the BLR in NHBLR could be reduced by the dual effects of (a) less scattering medium due to the reduced scattering volume given the small torus opening angle and (b) the increased torus obscuration between the observer and the scattering region. These effects give a reasonable explanation for the lack of observed HBLR in some type-2 AGNs.

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    78
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  • AKARI infrared camera observations of the 3.3 mu m PAH feature in Swift/BAT AGNs

    Angel Castro, Takamitsu Miyaji, Mai Shirahata, Kohei Ichikawa, Shinki Oyabu, David M. Clark, Masatoshi Imanishi, Takao Nakagawa, Yoshihiro Ueda

    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN   66 ( 6 )  2014.12  [Refereed]

     View Summary

    We explore the relationships between the 3.3 mu m polycyclic aromatic hydrocarbon (PAH) feature and active galactic nucleus (AGN) properties of a sample of 54 hard X-ray selected bright AGNs, including both Seyfert 1 and Seyfert 2 type objects, using the InfraRed Camera (IRC) on board the infrared astronomical satellite AKARI. The sample is selected from the nine-month Swift/BAT survey in the 14-195 keV band and all of them have measured X-ray spectra at E less than or similar to 10 keV. These X-ray spectra provide measurements of the neutral hydrogen column density (N-H) towards the AGNs. We use the 3.3 mu m PAH luminosity (L-3.3 mu m) as a proxy for star-formation activity and hard X-ray luminosity (L14-195 keV) as an indicator of the AGN activity. We search for possible differences in star-formation activity between type 1 (unabsorbed) and type 2 (absorbed) AGNs. We have made several statistical analyses taking the upper limits of the PAH lines into account utilizing survival analysis methods. The results of our log (L14-195 keV) versus log (L-3.3 mu m) regression show a positive correlation and the slope for the type 1/unobscured AGNs is steeper than that of type 2/obscured AGNs at a 3 sigma level. Our analysis also shows that the circumnuclear star formation is more enhanced in type 2/absorbed AGNs than type 1/unabsorbed AGNs for low X-ray luminosity/low Eddington ratio AGNs, while there is no significant dependence of star-formation activities on the AGN type in the high X-ray luminosities/Eddington ratios.

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    7
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  • POLARIZED MID-INFRARED SYNCHROTRON EMISSION IN THE CORE OF CYGNUS A

    E. Lopez-Rodriguez, C. Packham, C. Tadhunter, R. Mason, E. Perlman, A. Alonso-Herrero, C. Ramos Almeida, K. Ichikawa, N. A. Levenson, J. M. Rodriguez-Espinosa, C. A. Alvarez, E. A. Ramirez, C. M. Telesco

    ASTROPHYSICAL JOURNAL   793 ( 2 )  2014.10  [Refereed]

     View Summary

    We present high-angular (similar to 0 ''.4) resolution mid-infrared (MIR) polarimetric observations in the 8.7 mu m and 11.6 mu m filters of Cygnus A using CanariCam on the 10.4 m Gran Telescopio CANARIAS. A highly polarized nucleus is observed with a degree of polarization of 11% +/- 3% and 12% +/- 3% and a position angle of polarization of 27 degrees +/- 8 degrees and 35 +/- 8 in a 0 ''.38 (similar to 380 pc) aperture for each filter. The observed rising of the polarized flux density with increasing wavelength is consistent with synchrotron radiation from the parsec-scale jet close to the core of Cygnus A. Based on our polarization model, the synchrotron emission from the parsec-scale jet is estimated to be 14% and 17% of the total flux density in the 8.7 mu m and 11.6 mu m filters, respectively. A blackbody component with a characteristic temperature of 220 K accounts for &gt; 75% of the observed MIR total flux density. The blackbody emission arises from a combination of (1) dust emission in the torus; and (2) diffuse dust emission around the nuclear region, but the contributions of the two components cannot be well-constrained in these observations.

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    13
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  • AKARI IRC 2.5-5 mu m SPECTROSCOPY OF INFRARED GALAXIES OVER A WIDE LUMINOSITY RANGE

    Kohei Ichikawa, Masatoshi Imanishi, Yoshihiro Ueda, Takao Nakagawa, Mai Shirahata, Hidehiro Kaneda, Shinki Oyabu

    ASTROPHYSICAL JOURNAL   794 ( 2 )  2014.10  [Refereed]

     View Summary

    We present the result of a systematic infrared 2.5-5 mu m spectroscopic study of 22 nearby infrared galaxies over a wide infrared luminosity range (10(10) L-circle dot &lt; L-IR &lt; 10(13) L-circle dot) obtained from the AKARI Infrared Camera (IRC). The unique band of the AKARI IRC spectroscopy enables us to access both the 3.3 mu m polycyclic aromatic hydrocarbon (PAH) emission feature from star-forming activity and the continuum of torus-dust emission heated by an active galactic nucleus (AGN). Applying our AGN diagnostics to the AKARI spectra, we discover 14 buried AGNs. The large fraction of buried AGNs suggests that AGN activity behind the dust is almost ubiquitous in ultra-/luminous infrared galaxies (U/LIRGs). We also find that both the fraction and energy contribution of buried AGNs increase with infrared luminosity from 10(10) L-circle dot to 10(13) L-circle dot, including normal infrared galaxies with L-IR &lt; 10(11) L-circle dot. The energy contribution from AGNs in the total infrared luminosity is only similar to 7% in LIRGs and similar to 20% in ULIRGs, suggesting that the majority of the infrared luminosity originates from starburst activity. Using the PAH emission, we investigate the luminosity relation between star formation and AGNs. We find that these infrared galaxies exhibit higher star formation rates than optically selected Seyfert galaxies with the same AGN luminosities, implying that infrared galaxies could be an early evolutionary phase of AGN.

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    33
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  • The narrow Fe K alpha line and the molecular torus in active galactic nuclei: an IR/X-ray view

    C. Ricci, Y. Ueda, K. Ichikawa, S. Paltani, R. Boissay, P. Gandhi, M. Stalevski, H. Awaki

    ASTRONOMY & ASTROPHYSICS   567   id. A142  2014.07  [Refereed]

     View Summary

    The narrow component of the iron K alpha is an almost ubiquitous feature in the X-ray spectra of active galactic nuclei (AGN) and is believed to originate in neutral material, possibly located in the molecular torus. This would imply a tight connection between the Fe K alpha equivalent width (EW) and the physical properties of the torus. In a recent work we have shown that the decrease in the covering factor of the torus with the luminosity, as expected by luminosity-dependent unification models, would be able to explain the decrease in be K alpha EW with the luminosity (i.e. the X-ray Baldwin effect). Recent developments in the study of the mid-IR (MIR) spectrum of AGN allow important parameters of the torus to be deduced, such as its covering factor (f(obs)) and equatorial column density (N-H(T)). by applying clumpy torus models. Using XMM-Newton/EPIC observations of a sample of 24 type-I AGN, we investigate the relation between the physical parameters of the torus obtained by recent MIR works and the properties of the Fe K alpha line. We correct the values of the Fe K alpha LW by taking the inclination angle, the photon index, the equatorial column density, and half opening angle of the torus into account using a physical torus model of X-ray reprocessed radiation. We find that the relation between be K alpha LW and f(obs) shows a slope that is consistent with the expected value, albeit with low statistical significance. A trend that is consistent with the theoretical prediction is also found when comparing the Fe K alpha LW to N. Our work seems to confirm that the bulk of the narrow Fe K alpha line is produced by the same material responsible for the MIR emission.

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  • What obscures low-X-ray-scattering active galactic nuclei?

    S. F. Honig, P. Gandhi, D. Asmus, R. F. Mushotzky, R. Antonucci, Y. Ueda, K. Ichikawa

    MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY   438 ( 1 ) 647 - 656  2014.02  [Refereed]

     View Summary

    X-ray surveys have revealed a new class of active galactic nuclei (AGN) with a very low observed fraction of scattered soft X-rays, f(scat) &lt;0.5 per cent. Based on X-ray modelling, these 'X-ray new-type', or low observed X-ray-scattering (hereafter, 'low-scattering') sources have been interpreted as deeply buried AGN with a high covering factor of gas. In this paper, we address the questions whether the host galaxies of low-scattering AGN may contribute to the observed X-ray properties, and whether we can find any direct evidence for high covering factors from the infrared (IR) emission. We find that X-ray low-scattering AGN are preferentially hosted by highly inclined galaxies or merger systems as compared to other Seyfert galaxies, increasing the likelihood that the line of sight towards the AGN intersects with high columns of host-galactic gas and dust. Moreover, while a detailed analysis of the IR emission of low-scattering AGN ESO 103-G35 remains inconclusive, we do not find any indication of systematically higher dust covering factors in a sample of low-scattering AGN based on their IR emission. For ESO 103-G35, we constrained the temperature, mass and location of the IR emitting dust which is consistent with expectations for the dusty torus. However, a deep silicate absorption feature probably from much cooler dust suggests an additional screen absorber on larger scales within the host galaxy. Taking these findings together, we propose that the low f(scat) observed in low-scattering AGN is not necessarily the result of circumnuclear dust but could originate from interference of host-galactic gas with a column density of the order of 10(22) cm(-2) with the line of sight. We discuss implications of this hypothesis for X-ray models, high-ionization emission lines and observed star formation activity in these objects.

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    13
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  • A 2.5-5 μm spectroscopic study of hard X-ray selected AGNs with AKARI

    A. Castro, T. Miyaji, M. Shirahata, S. Oyabu, D. Clark, K. Ichikawa, M. Imanishi, T. Nakagawa, Y. Ueda

    Proceedings of the International Astronomical Union   9 ( 304 ) 66 - 67  2014  [Refereed]

     View Summary

    We explore the relationships between the 3.3 μm polycyclic aromatic hydrocarbon (PAH) feature and active galactic nucleus (AGN) properties of a sample of 54 hard X-ray selected bright AGNs, including both Seyfert 1 and Seyfert 2 type objects, using the InfraRed Camera (IRC) on board the infrared astronomical satellite AKARI. The sample is selected from the 9-month Swift/BAT survey in the 14-195 keV band and all of them have measured X-ray spectra at E ≲ 10 keV. These X-ray spectra provide measurements of the neutral hydrogen column density (N H) towards the AGNs. We use the 3.3 μm PAH luminosity (L 3.3μm) as a proxy for star formation activity and hard X-ray luminosity (L 14-195keV) as an indicator of the AGN activity. We searched for possible difference of star-formation activity between type 1 (un-absorbed) and type 2 (absorbed) AGNs. Our regression analysis of log L 14-195keV versus log L 3.3μm shows a positive correlation and the slope seems steeper for type 1/unobscured AGNs than that of type 2/obscured AGNs. The same trend has been found for the log (L 14-195keV/M BH) versus log (L 3.3μm/MBH) correlation. Our analysis show that the circum-nuclear star-formation is more enhanced in type 2/absorbed AGNs than type 1/un-absorbed AGNs for low X-ray luminosity/low Eddington ratio AGNs. Copyright © International Astronomical Union 2014.

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  • Iron Kα emission in type-I and type-II active galactic nuclei

    C. Ricci, Y. Ueda, S. Paltani, K. Ichikawa, P. Gandhi, H. Awaki

    Monthly Notices of the Royal Astronomical Society   441 ( 4 ) 3622 - 3633  2014  [Refereed]

     View Summary

    The narrow Fe Kα line is one of the main signatures of the reprocessing of X-ray radiation from the material surrounding supermassive black holes, and it has been found to be omnipresent in the X-ray spectra of active galactic nuclei (AGN). In this work, we study the characteristics of the narrow Fe Kα line in different types of AGN. Using the results of a large Suzaku study, we find that Seyfert 2s have on average lower Fe Kα luminosities than Seyfert 1s for the same 10- 50 keV continuum luminosity. Simulating dummy Seyfert 1s and Seyfert 2s populations using physical torus models of X-ray reflected emission, we find that this difference can be explained by means of different average inclination angles with respect to the torus, as predicted by the unified model. Alternative explanations include differences in the intensities of Compton humps, in the photon index distributions or in the average iron abundances. We show that the ratio between the flux of the broad and narrow Fe Kα line in the 6.35-6.45 keV range depends on the torus geometry considered, and is on average &lt
    25 per cent and &lt
    15 per cent for type-I and type-II AGN, respectively. We find evidence of absorption of the narrow Fe Kα line flux in Compton-thick AGN, which suggests that part of the reflecting material is obscured. We estimate that on average in obscured AGN the reflected radiation from neutral material is seen through a column density which is 1/4 of that absorbing the primary X-ray emission. This should be taken into account in synthesis models of the CXB and when studying the luminosity function of heavily obscured AGN.We detect the first evidence of the X-ray Baldwin effect in Seyfert 2s, with the same slope as that found for Seyfert 1s, which suggests that themechanism responsible for the decrease of the equivalent width with the continuum luminosity is the same in the two classes of objects. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

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    69
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  • Precessing Warped Be Disk Triggering the Giant Outbursts in 2009 and 2011 in A 0535+262/V725 Tau

    Yuki Moritani, Daisaku Nogami, Atsuo T. Okazaki, Akira Imada, Eiji Kambe, Satoshi Honda, Osamu Hashimoto, Sahori Mizoguchi, Yuichi Kanda, Kozo Sadakane, Kohei Ichikawa

    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN   65 ( 4 )  2013.08  [Refereed]

     View Summary

    We carried out optical high-dispersion spectroscopic monitoring of the Be disk in a Be/X-ray binary, A 0535+262/V725 Tau, from 2009 to 2012, covering two giant outbursts and several normal ones. This monitoring was performed in order to investigate any variabilities of the Be disk due to interactions with the neutron star in the recent X-ray active phase from 2008 to 2011. Such variabilities give a clue to any uncleared detailed mechanism for very bright X-ray outbursts, which are unique to some Be/X-ray binaries with a relatively wide and eccentric orbit. In a previous letter (Moritani et al. 2011, PASJ, 63, L25), a brief overview of the line-profile variabilities around the 2009 giant outburst was given, and the possibility of a warped Be disk was discussed. In this paper, a full analysis of the Ha line profiles as well as other line profiles is carried out. A bright blue component, or blue "shoulder," showing up after periastron indicates the presence of a dense gas stream toward the neutron star, which is associated with observed outbursts. We re-analyze the Ha line profiles before 2009 (down to 2005) in order to investigate the variability of the disk structure in the innermost region, which seems to have detached from the Be star surface by 2008. A redshifted enhanced component is remarkable in all emission lines observed around the 2009 giant outburst, occasionally forming a triple peak. These features indicate that the Be disk was warped in the X-ray active phase. We estimated the position of the warped region from fitting the radial velocity of the redshifted enhanced component of Ha, and found that it was very close to the periastron when two giant outbursts in 2009 and 2011 and a bright normal outburst in 2010 March occurred. These facts strongly suggest that the precessing warped Be disk triggered these giant outbursts.

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    37
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  • Infrared 3-4 mu m Spectroscopy of Nearby PG QSOs and AGN-Nuclear Starburst Connections in High-Luminosity AGN Populations (vol 63, pg S447, 2011)

    Masatoshi Imanishi, Kohei Ichikawa, Tomoe Takeuchi, Nozomu Kawakatu, Nagisa Oi, Keisuke Imase

    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN   64 ( 6 )  2012.12  [Refereed]

    DOI

  • Initial Results from Nobeyama Molecular Gas Observations of Distant Bright Galaxies

    Iono, D, Hatsukade, B, Kohno, K, Kawabe, R, Ikarashi, S, Ichikawa, K, Kodama, T, Motohara, K, Nakajima, T, Nakanishi, K, Ohta, K, Ota, K, Saito, T, Suzuki, K, Tadaki, K.-i, Tamura, Y, Ueda, J, Umehata, H, Yabe, K, Yoshida, T, Yuma, S, Kuno, N, Takano, S, Iwashita, H, Handa, K, Higuchi, A, Hirota, A, Ishikawa, S, Kimura, K, Maekawa, J, Mikoshiba, H, Miyazawa, C, Miyazawa, K, Muraoka, K, Ogawa, H, Onodera, S, Saito, Y, Sakai, T, Takahashi, S, Yun, M. S

    Publications of the Astronomical Society of Japan   64   L2  2012.08  [Refereed]

    DOI

  • Initial results from nobeyama molecular gas observations of distant bright galaxies

    Daisuke Iono, Bunyo Hatsukade, Kotaro Kohno, Ryohei Kawabe, Soh Ikarashi, Kohei Ichikawa, Tadayuki Kodama, Kentaro Motohara, Taku Nakajima, Koichiro Nakanishi, Kouji Ohta, Kazuaki Ota, Toshiki Saito, Kenta Suzuki, Ken-Ichi Tadaki, Yoichi Tamura, Junko Ueda, Hideki Umehata, Kiyoto Yabe, Tessei Yoshida, Suraphong Yuma, Nario Kuno, Shuro Takano, Hiroyuki Iwashita, Kazuyuki Handa, Aya Higuchi, Akihiko Hirota, Shinichi Ishikawa, Kimihiro Kimura, Jun Maekawa, Hiroshi Mikoshiba, Chieko Miyazawa, Kazuhiko Miyazawa, Kazuyuki Muraoka, Hideo Ogawa, Sachiko Onodera, Yasufumi Saito, Takeshi Sakai, Shigeru Takahashi, Min S. Yun

    Publications of the Astronomical Society of Japan   64 ( 4 ) L2  2012.08  [Refereed]

     View Summary

    We present initial results from the CO survey toward high-redshift galaxies using the Nobeyama 45m telescope. Using a new wide bandwidth spectrometer equipped with a two-beam SIS receiver, we have obtained three new detections of high-redshift (z = 1.6-3.4) submillimeter galaxies (SXDF 1100.001/HXMM02, SDP9, and SDP17), one tentative detection (SDSS J160705+533558), and one non-detection (COSMOS-AzTEC1). The galaxies observed during the commissioning phase are sources with known spectroscopic redshifts from previous optical or wide-band submillimeter spectroscopy. The derived molecular gas mass and line widths from Gaussian fits are ∼ 1011 M⊙ and 430-530km s -1, respectively, which are consistent with previous CO observations of distant submillimeter galaxies and quasars. The spectrometer, which realizes a maximum of 32 GHz instantaneous bandwidth, will provide new science capabilities at the Nobeyama 45m telescope, allowing us to determine redshifts of bright submillimeter selected galaxies without any prior redshift information. © 2012. Astronomical Society of Japan.

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    16
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  • INFRARED AND HARD X-RAY DIAGNOSTICS OF ACTIVE GALACTIC NUCLEUS IDENTIFICATION FROM THE SWIFT/BAT AND AKARI ALL-SKY SURVEYS

    K. Matsuta, P. Gandhi, T. Dotani, T. Nakagawa, N. Isobe, Y. Ueda, K. Ichikawa, Y. Terashima, S. Oyabu, I. Yamamura, L. Stawarz

    ASTROPHYSICAL JOURNAL   753 ( 2 )  2012.07  [Refereed]

     View Summary

    We combine data from two all-sky surveys in order to study the connection between the infrared and hard X-ray (&gt; 10 keV) properties for local active galactic nuclei (AGNs). The Swift Burst Alert Telescope all-sky survey provides an unbiased, flux-limited selection of hard X-ray-detected AGNs. Cross-correlating the 22 month hard X-ray survey with the AKARI all-sky survey, we studied 158 AGNs detected by the AKARI instruments. We find a strong correlation for most AGNs between the infrared (9, 18, and 90 mu m) and hard X-ray (14-195 keV) luminosities, and quantify the correlation for various subsamples of AGNs. Partial correlation analysis confirms the intrinsic correlation after removing the redshift contribution. The correlation for radio galaxies has a slope and normalization identical to that for Seyfert 1 galaxies, implying similar hard X-ray/infrared emission processes in both. In contrast, Compton-thick (CT) sources show a large deficit in the hard X-ray band, because high gas column densities diminish even their hard X-ray luminosities. We propose two photometric diagnostics for source classification: one is an X-ray luminosity versus infrared color diagram, in which type 1 radio-loud AGNs are well isolated from the others in the sample. The other uses the X-ray versus infrared color as a useful redshift-independent indicator for identifying CT AGNs. Importantly, CT AGNs and starburst galaxies in composite systems can also be differentiated in this plane based upon their hard X-ray fluxes and dust temperatures. This diagram may be useful as a new indicator to classify objects in new and upcoming surveys such as WISE and NuSTAR.

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    34
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  • MID- AND FAR-INFRARED PROPERTIES OF A COMPLETE SAMPLE OF LOCAL ACTIVE GALACTIC NUCLEI

    Kohei Ichikawa, Yoshihiro Ueda, Yuichi Terashima, Shinki Oyabu, Poshak Gandhi, Keiko Matsuta, Takao Nakagawa

    ASTROPHYSICAL JOURNAL   754 ( 1 )  2012.07  [Refereed]

     View Summary

    We investigate the mid-(MIR) to far-infrared (FIR) properties of a nearly complete sample of local active galactic nuclei (AGNs) detected in the Swift/Burst Alert Telescope (BAT) all-sky hard X-ray (14-195 keV) survey, based on the cross correlation with the AKARI infrared survey catalogs complemented by those with Infrared Astronomical Satellite and Wide-field Infrared Survey Explorer. Out of 135 non-blazer AGNs in the Swift/BAT nine-month catalog, we obtain the MIR photometric data for 128 sources either in the 9, 12, 18, 22, and/or 25 mu m band. We find good correlation between their hard X-ray and MIR luminosities over three orders of magnitude (42 &lt; log lambda L-lambda (9, 18 mu m) &lt; 45), which is tighter than that with the FIR luminosities at 90 mu m. This suggests that thermal emission from hot dusts irradiated by the AGN emission dominate the MIR fluxes. Both X-ray unabsorbed and absorbed AGNs follow the same correlation, implying isotropic infrared emission, as expected in clumpy dust tori rather than homogeneous ones. We find excess signals around 9 mu m in the averaged infrared spectral energy distribution from heavy obscured "new type" AGNs with small scattering fractions in the X-ray spectra. This could be attributed to the polycyclic aromatic hydrocarbon emission feature, suggesting that their host galaxies have strong starburst activities.

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    91
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  • Key Science Drivers for MICHI, A Mid-IR Instrument Concept for the TMT

    Chris Packham, M. Honda, M. Richter, Y. K. Okamoto, H. Kataza, T. Onaka, T. Fujiyoshi, Alan Tokunaga, M. Chun, A. Alonso-Herrero, J. Carr, M. Chiba, K. Enya, H. Fujiwara, P. Gandhi, M. Imanishi, K. Ichikawa, Y. Ita, N. Kawakatsu, T. Kotani, N. Levenson, T. Matsuo, M. Matsuura, T. Minezaki, J. Najita, N. Oi, T. Ootsubo, I. Sakon, M. Takami, C. Telesco, C. M. Wright, T. Yamashita

    GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY IV   8446  2012

     View Summary

    A mid-infrared (MIR) imager and spectrometer is being investigated for possible construction in the early operation of the Thirty Meter Telescope (TMT). Combined with the MIR adaptive optics (AO) system (MIRAO), the instrument will afford similar to 15 times higher sensitivity and similar to 4 times better spatial resolution (0.07") at 10 mu m compared to 8m-class telescopes. Additionally, through exploiting the large collection area of the TMT, the high-dispersion spectroscopy mode will be unrivaled by other ground-and space-based facilities. These combined capabilities offer the possibility for breakthrough science, as well as 'workhorse' observing modes of imaging and low/moderate spectral resolution. In this paper we summarize the primary science drivers that are guiding the instrument design.

    DOI

    Scopus

    14
    Citation
    (Scopus)
  • A 2.5-5 μm spectroscopic study of hard X-ray selected AGNs using AKARI infrared camera

    A. Castro, T. Miyaji, T. Nakagawa, M. Shirahata, S. Oyabu, M. Imanishi, Y. Ueda, K. Ichikawa

    Proceedings of Science   2012-November  2012

     View Summary

    We present results of the 2.5-5 μm spectroscopy of a sample of hard X-ray selected active galactic nuclei (AGNs) using the grism mode of the InfraRed Camera (IRC) on board the infrared astronomical satellite AKARI. The sample is selected from the 9-month Swift/BAT survey in the 14-195 keV band, which provides a fair sample of AGNs including highly absorbed ones. The 2.5-5 μm spectroscopy provide a strong diagnostic tool for the circumnuclear environment of AGNs through the continuum shapes and emission/absorption features such as the 3.3 μm polycyclic aromatic hydrocarbon (PAH) emission and the broad 3.1 μm H2O ice, 3.4 μm bare carbonaceous dust, 4.26 μm CO2 and 4.67 μm CO absorptions. As our first step, we use the 3.3 μm PAH emission as a proxy for the star-formation activity and searched for possible difference of star-formation activity between type 1 (unabsorbed) and type 2 (absorbed) AGNs. We found no significant dependence of the 3.3 μm PAH line luminosity, normalized by the black hole mass, on optical AGNs types or the X-ray measured column densities.

  • Drastic Spectroscopic Variability of the Be/X-Ray Binary Ariel 0535+262/V725 Tau during and after the 2009 Giant Outburst

    Yuuki Moritani, Daisaku Nogami, Atsuo T. Okazaki, Akira Imada, Eiji Kambe, Satoshi Honda, Osamu Hashimoto, Kohei Ichikawa

    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN   63 ( 4 ) L25 - L29  2011.08  [Refereed]

     View Summary

    We report on high-dispersion optical spectroscopic observations of the Be/X-ray binary A 0535+262/V725 Tau during a giant outburst in 2009 November/December, and after it. The observed emission line profiles, reflecting the structure of the geometrically thin circumstellar envelope of the Be star (Be disk), show drastic variabilities, and indicate the existence of a warped component. The enhanced blue shoulder seen after periastron passage implies a gas stream from a dense part of the Be disk to the neutron star.

    DOI

    Scopus

    23
    Citation
    (Scopus)
  • SUBARU AND GEMINI HIGH SPATIAL RESOLUTION INFRARED 18 mu m IMAGING OBSERVATIONS OF NEARBY LUMINOUS INFRARED GALAXIES

    Masatoshi Imanishi, Keisuke Imase, Nagisa Oi, Kohei Ichikawa

    ASTRONOMICAL JOURNAL   141 ( 5 )  2011.05  [Refereed]

     View Summary

    We present the results of a ground-based, high spatial resolution infrared 18 mu m imaging study of nearby luminous infrared galaxies (LIRGs), using the Subaru 8.2 m and Gemini-South 8.1 m telescopes. The diffraction-limited images routinely achieved with these telescopes in the Q band (17-23 mu m) allow us to investigate the detailed spatial distribution of infrared emission in these LIRGs. We then investigate whether the emission surface brightnesses are modest, as observed in starbursts, or are so high that luminous active galactic nuclei (AGNs; high emission surface brightness energy sources) are indicated. The sample consists of 18 luminous buried AGN candidates and starburst-classified LIRGs identified in earlier infrared spectroscopy. We find that the infrared 18 mu m emission from the buried AGN candidates is generally compact, and the estimated emission surface brightnesses are high, sometimes exceeding the maximum value observed in and theoretically predicted for a starburst phenomenon. The starburst-classified LIRGs usually display spatially extended 18 mu m emission and the estimated emission surface brightnesses are modest, within the range sustained by a starburst phenomenon. The general agreement between infrared spectroscopic and imaging energy diagnostic methods suggests that both are useful tools for understanding the hidden energy sources of the dusty LIRG population.

    DOI

    Scopus

    31
    Citation
    (Scopus)
  • Infrared 3-4 mu m Spectroscopy of Nearby PG QSOs and AGN-Nuclear Starburst Connections in High-Luminosity AGN Populations

    Masatoshi Imanishi, Kohei Ichikawa, Tomoe Takeuchi, Nozomu Kawakatu, Nagisa Oi, Keisuke Imase

    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN   63   S447 - S456  2011.03  [Refereed]

     View Summary

    We present the results of infrared L-band (3-4 mu m) slit spectroscopy of 30 PG QSOs at z &lt; 0.17, a representative sample of local high-luminosity, optically selected AGNs. The 3.3 mu m polycyclic aromatic hydrocarbon (PAH) emission feature is used to probe nuclear (&lt; a few kpc) starburst activity and to investigate the connections between AGNs and nuclear starbursts in PG QSOs. The 3.3 mu m PAH emission is detected in the individual spectra of 5/30 of the observed PG QSOs. We constructed a composite spectrum of PAN-undetected PG QSOs and discerned the presence of the 3.3 mu m PAH emission therein. We estimated the nuclear-starburst and AGN luminosities from the observed 3.3 mu m PAH emission and 3.35 mu m continuum luminosities, respectively, and found that the nuclear-starburst-to-AGN luminosity ratios in PG QSOs are similar to those of previously studied AGN populations with lower luminosities, suggesting that AGN-nuclear starburst connections are valid over a wide luminosity range of AGNs in the local universe. The observed nuclear-starburst-to-AGN luminosity ratios in PG QSOs with available supermassive black-hole masses are comparable to a theoretical prediction based on the assumption that the growth of a supermassive black hole is controlled by starburst-induced turbulence.

    DOI

    Scopus

    34
    Citation
    (Scopus)

▼display all

Books and Other Publications

  • ngVLA-J memo series

    ( Part: Contributor, Section M003)

    2021

  • SPICAサイエンス検討会最終報告書

    SPICAサイエンス検討メンバー( Part: Contributor, 3.3章)

Presentations

  • Radio galaxy catalog in the Subaru/HSC Joint catalog field

    Kohei Ichikawa

    Tracing the SMBH growth: outlook beyond the HSC-SSP, and future collaborations 

    Presentation date: 2022.12

  • 歴史史料で探る過去の天文現象

    市川幸平

    第9回東北大学若手アンサンブルワークショップ 

    Presentation date: 2022.11

    Event date:
    2022.11
     
     
  • Recent observational progress on AGN studies

    Kohei Ichikawa  [Invited]

    IGM Galaxy workshop 2022 

    Presentation date: 2022.08

    Event date:
    2022.08
     
     
  • Rapidly growing supermassive black holes in extremely radio-loud galaxies

    Kohei Ichikawa

    IAU General Assembly IAU Symposium 373: Resolving the Rise and Fall of Star Formation in Galaxies 

    Presentation date: 2022.08

    Event date:
    2022.08
     
     
  • Rapidly growing supermassive black holes in extremely radio-loud galaxies

    Kohei Ichikawa

    IAU General Assembly Focused Meeting 1: Physics of relativistic jets on all scales 

    Presentation date: 2022.08

    Event date:
    2022.08
     
     
  • Rapidly growing supermassive black holes in extremely radio-loud galaxies

    Kohei Ichikawa

    COSPAR2022, Signature of Cosmic Black Holes 

    Presentation date: 2022.07

    Event date:
    2022.07
     
     
  • NuSTAR discovery of a dead quasar engine in Arp 187

    Kohei Ichikawa

    Ten Years of High-Energy Universe in Focus: NuSTAR 2022 

    Presentation date: 2022.06

    Event date:
    2022.06
     
     
  • eFEDS X-ray view of WERGS: Radio Galaxies selected by the Subaru/HSC and VLA/FIRST survey

    Kohei Ichikawa  [Invited]

    eROSITA consortium Meeting 2022 

    Presentation date: 2022.01

    Event date:
    2022.01
     
     
  • Fading AGN; New parameter space of 10^{3-4} yr-long AGN variability?

    Kohei Ichikawa  [Invited]

    Presentation date: 2021.12

    Event date:
    2021.12
     
     
  • Rapidly growing supermassive black holes in extremely radio-loud galaxies

    Kohei Ichikawa  [Invited]

    Summer workshop of Subaru Galactic Center Black Hole 

    Presentation date: 2021.09

    Event date:
    2021.09
     
     
  • Rapid SMBH growth in the extremely radio-loud galaxies

    Kohei Ichikawa

    European Astronomical Society meeting 2021 

    Presentation date: 2021.07

    Event date:
    2021.06
    -
    2021.07
  • Serendipitous Discovery Of Dying AGN In Arp 187

    Kohei Ichikawa

    238th American Astronomical Society Meeting 

    Presentation date: 2021.06

    Event date:
    2021.06
     
     
  • Dying AGN

    Kohei Ichikawa  [Invited]

    Kaffee Runde at MPE 

    Presentation date: 2021.05

    Event date:
    2021.05
     
     
  • Searching dying AGN

    Kohei Ichikawa  [Invited]

    BH IR observation meeting 

    Presentation date: 2020.03

    Event date:
    2020.03
     
     
  • Extremely radio loud galaxies

    Kohei Ichikawa

    Subaru/HSC AGN meeting 

    Presentation date: 2020.01

    Event date:
    2020.01
     
     
  • Obscured SMBH assembly using multi-wavelength and wide-field surveys

    Kohei Ichikawa  [Invited]

    Subaru 20: Optical and Infrared Astronomy for the next Decade 

    Presentation date: 2019.11

  • Seeing common or rare AGN with TMT

    Kohei Ichikawa  [Invited]

    TMT Science Forum 2019: Science Synergies in the era of the Thirty-Meter-Telescope 

    Presentation date: 2019.11

  • Discovery of Dying AGN in Arp 187: Experience of Drastic Luminosity Decline within 10^4 yr

    Kohei Ichikawa

    Presentation date: 2019.09

  • Complete IR View of Swift/BAT AGN

    Kohei Ichikawa

    AGN-Starburst meeting 2019 

    Presentation date: 2019.08

  • Gravitational Waves from SMBH binaries in U/HyLIRGs

    Kohei Ichikawa

    EWASS 2019 

    Presentation date: 2019.06

  • IR view of X-ray AGN: The covering factor of gas and dust in Swift/BAT AGN

    Kohei Ichikawa

    Supermassive black holes: Environment and Evolution 

    Presentation date: 2019.06

  • Complete IR View of Swift/BAT AGN

    Kohei Ichikawa

    6th Galaxy Evolution Workshop 

    Presentation date: 2019.06

  • Observation of Supermassive Black Holes

    Kohei Ichikawa  [Invited]

    6th SMBH liaison workshop 

    Presentation date: 2019.05

  • Covering factor of dust and gas in Swift/BAT AGN

    Kohei Ichikawa

    SPICA2019 

    Presentation date: 2019.05

  • WERGS: Optically-faint radio galaxies discovered by Subaru/HSC and VLA/FIRST

    Kohei Ichikawa  [Invited]

    HSC-eROSITA meeting 

    Presentation date: 2019.05

  • Extremely radio-loud AGN discovered by Subaru/HSC

    Kohei Ichikawa

    Extremely Big Eyes on the Early Universe 2019 

    Presentation date: 2019.03

  • The Covering Factor of Dust and Gas in Swift/BAT Active Galactic Nuclei

    Kohei Ichikawa

    Presentation date: 2019.03

  • The beginning and ending phase of AGN

    Kohei Ichikawa  [Invited]

    Kure AGN workshop 

    Presentation date: 2019.02

  • Host galaxy properties of pure-IR AGN

    Kohei Ichikawa

    BASS workshop 2019 

    Presentation date: 2019.02

  • Gravitational wave signals from SMBHs in Hy/ULIRGs

    Kohei Ichikawa

    East Asia high-z galaxy workshop 

    Presentation date: 2019.02

  • The Covering Factor of Dust and Gas in Swift/BAT AGN

    Kohei Ichikawa

    East Asia AGN workshop 2019 

    Presentation date: 2019.01

  • BASS Survey: The Covering Factor of Dust and Gas in Swift/BAT AGN

    Kohei Ichikawa

    TORUS2018: The many faces of the AGN obscuration 

    Presentation date: 2018.12

  • Extremely radio-loud AGN residing in low-mass galaxies discovered by HSC survey

    Kohei Ichikawa

    Formation and evolution of SMBHs  (Tohoku University, Sendai, Japan) 

    Presentation date: 2018.11

  • The complete IR view of the Swift/BAT 70 month AGN catalog

    Kohei Ichikawa

    42nd COSPAR Assembly 

    Presentation date: 2018.07

  • Dying AGN in Arp 187

    Kohei Ichikawa

    ASNY50 

    Presentation date: 2018.07

  • Looking at drastic AGN luminosity decline in Arp 187 within 10^4 years

    Kohei Ichikawa

    5th Galaxy Evolution Workshop 

    Presentation date: 2018.06

  • BAT AGN Spectroscopy Survey: The Covering Factor of Dust and Gas in Swift/BAT AGN

    Kohei Ichikawa

    NERQUAM2018 

    Presentation date: 2018.05

  • Is there a maximum mass for supermassive black holes?

    Kohei Ichikawa

    East Asian Young Astronomers Meeting 2017 

    Presentation date: 2017.11

▼display all

Research Projects

  • Rapid supermassive black hole growth revealed by multi-wavelength surveys

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

    Project Year :

    2020.04
    -
    2023.03
     

  • Revealing the close environment of supermassive black holes using the moon

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Early-Career Scientists

    Project Year :

    2018.04
    -
    2021.03
     

    Ichikawa Kohei

     View Summary

    We first applied the light curve fitting by the occultation event by a target, we first applied the light curve fitting to the large amount of the light curve data of stars to find a possible occultation of the trans Neptunian object. We have succeeded finding candidate and whose estimated size turned out to be the order of km. This result is summarized and published in the Nature Astronomy (Arimatsu et al. 2019). For the next step, we have also summarized the properties of one AGN catalog in the local universe, and this was also published in the Astrophysical Journal (Ichikawa et al. 2019).

  • 新たに見つかった活動銀河核種族から暴く銀河と中心ブラックホールの共進化

    日本学術振興会  科学研究費助成事業 特別研究員奨励費

    Project Year :

    2016.04
    -
    2019.03
     

    市川 幸平

     View Summary

    本年度は、3つの研究を行った。
    1つめは、「超巨大ブラックホールには質量の上限があるのか?」という問いに対する観測的研究である。超巨大ブラックホール (supermassive black holes; SMBHs) は活動銀河核 (active galactic nuclei; AGN) という非常に明るく輝く天体として観測されるが、SMBHの最大質量は概ね10^10太陽質量を超えたあたりであることがわかっている。つまり、SMBHはいったん10^10太陽質量になってしまったら、何かしらの理由でそれ以上太れなくなってしまうようである。理論研究によると、ガスはブラックホールまで落ちることなく、ほとんどの質量はoutflow/jetで外に放り出されてしまう。そこで、研究代表者はSDSSクエーサーカタログを用いて、ブラックホール質量ごとのジェットを出しているAGNの割合を求めてみたところ、10^9.3太陽質量を超えたあたりから、急激にジェットをもつAGNの割合が増えることを発見した。これは、上記の理論予測をサポートする初めての観測的結果となり、研究代表者が筆頭著者として、ApJに論文が出版された。また、2つ目の研究は、死につつあるAGNのダストトーラスの観測可能な期間についての結果がまとまり、研究代表者が筆頭著者としてApJに論文が出版された。また、研究代表者が昨年度取り組んだ、X線選択された活動銀河核の赤外線カタログを用いて、得られた赤外線光度から活動銀河核まわりのダスト立体角の見積もりを行った。また、その値をX線から示唆された立体角と比較したところ、X線から得られた立体角の方が平均的には必ず大きくなるという結果を得ることが出来た。X線から得られた立体角はダストとガスのいずれかをトレースする。そのため、活動銀河核の周辺には、ダストは存在しないものの、ガスで覆われた領域が存在することが示唆された。これらの結果は研究代表者が筆頭著者として、ApJに投稿を行った。

  • 赤外線とX線の両波長観測から探る新しい活動銀河核種族の解明

    日本学術振興会  科学研究費助成事業 研究活動スタート支援

    Project Year :

    2015.08
    -
    2017.03
     

    市川 幸平

     View Summary

    近傍で最もコンプリートなX線カタログであるSwift/BAT活動銀河カタログを親サンプルとして、赤外線衛星との位置マッチングを行うことで、約600天体にも及ぶ赤外線対応天体のカタログを作成した。現在、赤外線対応天体カタログをまとめた論文を準備中であり、それとともに特殊な環境をもつ活動銀河核種族も見つかってきたため、それらをとりまとめ、別個の論文として報告する予定である。具体的には、X線放射に比べて、赤外線放射が極端に暗い種族であるDFAGN、星生成起源のダスト放射が占めるはずの遠赤外線までも活動銀河核で明るく輝く種族などの報告である。さらに、これらのターゲットのうち、高空間分解能赤外線観測が得られたもの、あるいは赤外線のスペクトル分解の手法を用いることが可能な天体に対しては、赤外線クランプトーラスモデルの適応を予定している。また、可視光線や電波観測で発見された活動銀河核天体をX線、赤外線で探査したところ、本来検出できるべき明るさを持つはずが、まったく検出されない特殊な種族も発見した。これは、可視光線の挟輝線領域や電波ジェットが空間的に広がっている (kpcスケール) のに対して、赤外線を放射する領域は <10 pcと小さく、X線放射領域はさらに小さいことを考えると、現在、中心核の活動は止んでいるが、大きいスケールでは昔の活動銀河核活動で放射された輻射で明るく輝くため、今まさしく死につつある活動銀河核を捉えることになる。この死につつ有る活動銀河核を捉えた結果を論文としてまとめた (Ichikawa et al. 2016)。

  • 赤外・X線による埋もれた活動銀河の観測から探る超巨大ブラックホールと銀河の共進化

    日本学術振興会  科学研究費助成事業 特別研究員奨励費

    Project Year :

    2012.04
    -
    2015.03
     

    市川 幸平

     View Summary

    平成26年度に行った研究は、大きく2つのパートに別れる。1つ目は、超高光度赤外線銀河 (U/LIRGs) のエネルギー源の定量的な見積について。そして、2つ目は、高空間分解能赤外線観測から探る活動銀河核の統一モデルのさらなる理解についてである。
    1つ目の研究について、我々は赤外線衛星「あかり」の近赤外線分光観測によって得られたU/LIRGs約30天体に対して、スペクトルから活動銀河核由来の塵放射を分離し、埋もれた活動銀河核の探査のみならず、活動銀河核由来の赤外線放射を定量的に見積もった。その結果、赤外線光度が大きいほど、埋もれた活動銀河核の赤外線放射の割合は増えているが、その絶対値はたかだか20%であることがわかった。可視光で発見される活動銀河核ではこの割合はより大きいことを考えると、U/LIRGsは活動銀河核になりたての若い種族であり、今後さらに活動銀河核の放射が大きくなっていくことが予想できる。これらの結果がThe Astrophysical Journal誌にて出版された。
    2つめの研究について、我々はGemini望遠鏡およびVLT望遠鏡で取得された近傍の活動銀河核トーラス放射のスペクトルに対し、クランプトーラスモデルを適用することで、トーラスの大きさ・中心を覆う立体角などの物理パラメータを求めた。この結果、活動銀河核の種族によってトーラスの幾何構造は大きく異ることがわかり、その結果がまとまり、The Astrophysical Journal誌にて受理され、出版予定である。

Misc

  • Importance of Dust in the Evolution of Galaxies: Prospect for SPICA

    竹内努, 泉拓磨, 今西昌俊, 久保真理子, 播金優一, 馬場俊介, 山下拓時, 田村陽一, 梅畑豪紀, 鳥羽儀樹, 長峯健太郎, 橋本拓也, 市川幸平, 和田武彦

    日本天文学会年会講演予稿集   2020  2020

    J-GLOBAL

  • 最期を迎えた超巨大ブラックホールの発見 〜死を迎えても輝きを失わないブラックホール〜

    市川幸平

    東北大学理学研究科ニュース    2019.04  [Invited]

    Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)  

  • Active Galactic Nucleus caught in the act of "dying" 〜light echo delivers the information before the death〜

    Kohei Ichikawa

    NEWS in Graduate School of Science at Tohoku University    2019.04  [Invited]

  • AKARI/IRCを用いた,赤外線銀河内の埋もれた活動銀河核の探査とその赤外線光度への寄与の見積もり

    市川幸平, 上田佳宏, 今西昌俊, 中川貴雄, 白旗麻衣, 金田英宏, 大薮進喜

    日本天文学会年会講演予稿集   2014  2014

    J-GLOBAL

  • あかり2.5-5.0μm分光観測による赤外線銀河中の埋もれた活動銀河核の探査

    市川幸平, 今西昌俊, 白旗麻衣, 中川貴雄, 上田佳宏

    日本天文学会年会講演予稿集   2012  2012

    J-GLOBAL

  • 「あかり」赤外線全天サーベイカタログとSwift/BAT硬X線全天サーベイカタログを用いた活動銀河核の光度相関(I)

    松田桂子, 松田桂子, GANDHI Poshak, 堂谷忠靖, 市川幸平, 上田佳宏, 寺島雄一, 中川貴雄, 大藪進喜

    日本天文学会年会講演予稿集   2011  2011

    J-GLOBAL

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Syllabus

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Teaching Experience

  • 学問論演習 (1年生後期)

    Tohoku University  

    2022.10
    -
    2023.02
     

  • Undergraduate research program

    Tohoku University  

    2020.04
    -
    2021.03
     

  • 天文学セミナー (3年生向け; 2019年度後期)

    東北大学  

  • 基礎ゼミ (1年生向け; 2019年度前期)

    東北大学  

 

Social Activities

  • 東北大学ILASコロキウム

    東北大学 

    2022.11
     
     

  • 天文学者的 超巨大ブラックホールの見かたと成長の見守りかた

    自然科学カフェ 

    2021.02
     
     

  • もしも君が杜の都で天文学者になったら

    東北大学理学研究科天文学専攻 

    2019.12
     
     

  • 総研大キャリア支援セミナー

    総研大 

    2019.08
     
     

Sub-affiliation

  • Faculty of Science and Engineering   Graduate School of Advanced Science and Engineering