Updated on 2025/06/23

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

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  

  • Distinguished Researcher at Tohoku University

    2022.05   Tohoku University  

  • 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

▼display all

 

Papers

  • Implication of Galaxy-scale Negative Feedback by One of the Most Powerful Multiphase Outflows in a Hyperluminous Infrared Galaxy at Intermediate Redshift

    Xiaoyang Chen, Masayuki Akiyama, Kohei Ichikawa, Yoshiki Toba, Toshihiro Kawaguchi, Takuma Izumi, Toshiki Saito, Daisuke Iono, Masatoshi Imanishi, Kianhong Lee, Hiroshi Nagai, Hirofumi Noda, Abdurro’uf, Mitsuru Kokubo, Naoki Matsumoto

    The Astrophysical Journal   979 ( 1 ) 32 - 32  2025.01

     View Summary

    Abstract

    Powerful galactic outflows driven by active galactic nuclei (AGNs) are commonly considered as one of the main mechanisms to regulate star formation in massive galaxies. Ultra- and hyperluminous IR galaxies (U/HyLIRGs) are thought to represent a transition phase of galaxies from a rapidly growing period to a quiescent status as gas is swept out by outflows, providing a laboratory in which to investigate outflows and their feedback effects on hosts. In this paper we report recent Gemini and Atacama Large Millimeter/submillimeter Array (ALMA) observations of a HyLIRG, J1126, at z = 0.46842, which has been identified with a puzzling coexistence of a fast ionized outflow (>2000 km s−1) and an intense starburst (star formation rate of 800 M yr−1). The Gemini observation shows the fast ionized outflow is extended to several kiloparsecs with a mass-loss rate of 180 M yr−1. A massive molecular outflow with a high mass-loss rate (2500 M yr−1) is revealed by ALMA. The multiphase outflows show large factors of momentum boost and loading of kinetic power, indicating a driving by the thermal pressure of a nuclear hot wind and/or the radiation pressure of a highly obscured AGN. In addition to ejection of kinetic energy, it is also found that the powerful outflow can induce an ionizing shock in the galaxy disk and enhance the excitation and dissociation of molecular gas. The powerful outflow probably results in an instantaneous negative feedback and shows potential to regulate host growth in the long term.

    DOI

    Scopus

  • A Wide and Deep Exploration of Radio Galaxies with Subaru HSC (WERGS). X. The Massive and Passive Nature of Radio Galaxies at z ∼ 4

    Yuta Yamamoto, Tohru Nagao, Takuji Yamashita, Hisakazu Uchiyama, Mariko Kubo, Yoshiki Toba, Yuichi Harikane, Kohei Ichikawa, Masaru Kajisawa, Akatoki Noboriguchi, Yoshiaki Ono, Toshihiro Kawaguchi

    The Astrophysical Journal   978 ( 1 ) 102 - 102  2024.12

     View Summary

    Abstract

    High-z radio galaxies (HzRGs) are considered important objects for understanding the formation and evolution of massive galaxies in the early Universe. However, until to date, detailed studies of the stellar population of HzRGs, such as the star formation history, have been scarce. Therefore, this study conducted a new survey to establish a less-biased sample of HzRGs and consequently investigate their properties. We utilized a sample of g-dropout Lyman break galaxies (LBGs) obtained from an optical wide and deep imaging survey made by Subaru Hyper Suprime-Cam. Based on the cross matching of this LBG sample with the Very Large Array Faint Images of the Radio Sky at Twenty cm radio survey data, we constructed a photometric sample of HzRGs at z ∼ 4 for a ∼560 deg2 survey field. Consequently, we identified 146 HzRG candidates. To analyze the characteristics of these candidates, we focus on objects exhibiting the near-infrared photometry of VIKING or UKIRT Infrared Deep Sky Survey and the mid-infrared photometry of unWISE (28 objects). The results indicate that seven objects exhibit spectral energy distributions (SEDs) consistent with galaxies at z ∼ 4. The HzRG candidates have very large stellar masses with ∼4.2 × 1011 M on average. This stellar mass is similar to that of previously discovered ultra-steep-spectrum HzRGs at z ∼ 4, though our sample is affected by a sample selection bias that selects only HzRGs with M > 1011 M . Further, the SEDs of those HzRG candidates suggest a past fast quenching with a rough timescale of ∼0.1 Gyr, as evidenced from the rest-frame UVJ diagram.

    DOI

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  • BASS. XLI. The Correlation between Mid-infrared Emission Lines and Active Galactic Nuclei Emission

    M. Bierschenk, C. Ricci, M. J. Temple, S. Satyapal, J. Cann, Y. Xie, Y. Diaz, K. Ichikawa, M. J. Koss, F. E. Bauer, A. Rojas, D. Kakkad, A. Tortosa, F. Ricci, R. Mushotzky, T. Kawamuro, K. K. Gupta, B. Trakhtenbrot, C. S. Chang, R. Riffel, K. Oh, F. Harrison, M. Powell, D. Stern, C. M. Urry

    Astrophysical Journal   976 ( 2 )  2024.12

     View Summary

    We analyze Spitzer spectra of 140 active galactic nuclei (AGN) detected in the hard X-rays (14-195 keV) by the Burst Alert Telescope on board Swift. This sample allows us to probe several orders of magnitude in black hole masses (106-109 M ⊙), Eddington ratios (10−3-1), X-ray luminosities (1042-1045 erg s−1), and X-ray column densities (1020-1024 cm−2). The AGN emission is expected to be the dominant source of ionizing photons with energies ≳50 eV, and therefore, high-ionization mid-infrared (MIR) emission lines such as [Ne v] 14.32, 24.32 μm and [O iv] 25.89 μm are predicted to be good proxies of AGN activity, and robust against obscuration effects. We find high detection rates (≳85%-90%) for the MIR coronal emission lines in our AGN sample. The luminosities of these lines are correlated with the 14-150 keV luminosity (with a typical scatter of σ ∼0.4-0.5 dex), strongly indicating that the MIR coronal line (CL) emission is driven by AGN activity. CLs are also tightly correlated to the bolometric luminosity (σ ∼0.2-0.3 dex), calculated from careful analysis of the spectral energy distribution. We find that the relationship between the CL strengths and L 14-150 keV is independent of black hole mass, AGN luminosity, and Eddington ratio, and mostly not affected by high X-ray column densities. This confirms that the MIR CLs can be used as unbiased tracers of the AGN power for X-ray luminosities in the 1042-1045 erg s−1 range.

    DOI

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  • Birth of Rapidly Spinning, Overmassive Black Holes in the Early Universe

    Kohei Inayoshi, Kohei Ichikawa

    Astrophysical Journal Letters   973 ( 2 )  2024.10

     View Summary

    The James Webb Space Telescope (JWST) has unveiled numerous massive black holes (BHs) in faint, broad-line active galactic nuclei (AGNs). The discovery highlights the presence of dust-reddened AGN populations, referred to as “little red dots (LRDs),” more abundant than X-ray-selected AGNs, which are less influenced by obscuration. This finding indicates that the cosmic growth rate of BHs within this population does not decrease but rather increases at higher redshifts beyond z ∼ 6. The BH accretion rate density deduced from their luminosity function is remarkably higher than that from other AGN surveys in X-ray and infrared bands. To align the cumulative mass density accreted to BHs with the observed BH mass density at z ≃ 4-5, as derived from the integration of the BH mass function, the radiative efficiency must be doubled from the canonical 10% value, achieving significance beyond the >3σ confidence level. This suggests the presence of rapid spins with 96% of the maximum limit among these BHs under the thin-disk approximation, maintained by prolonged mass accretion instead of chaotic accretion with randomly oriented inflows. Moreover, we derive an upper bound for the stellar mass of galaxies hosting these LRDs, ensuring consistency with galaxy formation in the standard cosmological model, where the host stellar mass is limited by the available baryonic reservoir. Our analysis gives a lower bound for the BH-to-galaxy mass ratio that exceeds the typical value known in the nearby universe and aligns with that for JWST-detected unobscured AGNs. Accordingly, we propose a hypothesis that the dense, dust-rich environments within LRDs facilitate the emergence of rapidly spinning and overmassive BH populations during the epoch of reionization. This scenario predicts a potential association between relativistic jets and other high-energy phenomena with overmassive BHs in the early universe.

    DOI

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    12
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  • Ongoing and Fossil Large-scale Outflows Detected in a High-redshift Radio Galaxy: [C ii] Observations of TN J0924-2201 at z = 5.174

    Kianhong Lee, Masayuki Akiyama, Kotaro Kohno, Daisuke Iono, Masatoshi Imanishi, Bunyo Hatsukade, Hideki Umehata, Tohru Nagao, Yoshiki Toba, Xiaoyang Chen, Fumi Egusa, Kohei Ichikawa, Takuma Izumi, Naoki Matsumoto, Malte Schramm, Kenta Matsuoka

    Astrophysical Journal   972 ( 1 )  2024.09  [Refereed]

     View Summary

    We present Atacama Large Millimeter/submillimeter Array observations of the [C ii] 158 μm line and the underlying continuum emission of TN J0924−2201, which is one of the most distant known radio galaxies at z > 5. The [C ii] line and 1 mm continuum emission are detected at the host galaxy. The systemic redshift derived from the [C ii] line is z [C II] = 5.1736 ± 0.0002, indicating that the Lyα line is redshifted by a velocity of 1035 ± 10 km s−1, marking the largest velocity offset between the [C ii] and Lyα lines recorded at z > 5 to date. In the central region of the host galaxy, we identify a redshifted substructure of [C ii] with a velocity of 702 ± 17 km s−1, which is close to the C iv line with a velocity of 500 ± 10 km s−1. The position and the velocity offsets align with a model of an outflowing shell structure, consistent with the large velocity offset of Lyα. The nondetection of [C ii] and dust emission from the three CO(1-0)-detected companions indicates their different nature compared to dwarf galaxies, based on the photodissociation region model. Given their large velocity of ∼1500 km s−1, outflowing molecular clouds induced by the active galactic nucleus are the most plausible interpretation, and they may exceed the escape velocity of a 1013 M ⊙ halo. These results suggest that TN J0924−2201, with ongoing and fossil large-scale outflows, is in a distinctive phase of removing molecular gas from a central massive galaxy in an overdense region in the early Universe. A dusty H i absorber at the host galaxy is an alternative interpretation.

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  • Exploring Low-mass Black Holes through Tidal Disruption Events in the Early Universe: Perspectives in the Era of the JWST, Roman Space Telescope, and LSST Surveys

    Kohei Inayoshi, Kazumi Kashiyama, Wenxiu Li, Yuichi Harikane, Kohei Ichikawa, Masafusa Onoue

    Astrophysical Journal   966 ( 2 )  2024.05  [Refereed]

     View Summary

    The James Webb Space Telescope (JWST) has recently uncovered the presence of low-luminosity active galactic nuclei (AGNs) at z = 4-11. Spectroscopic observations have provided estimates of the nuclear black hole (BH) masses for these sources, extending the low-mass boundary down to M • ∼ 106-7 M ⊙. Despite this breakthrough, the observed lowest mass of BHs is still ≳1-2 orders of magnitude heavier than the predicted mass range of their seed population, thereby leaving the initial mass distribution of massive BHs poorly constrained. In this paper, we focus on UV-to-optical (in the rest frame) flares of stellar tidal disruption events (TDEs) embedded in low-luminosity AGNs as a tool for exploring low-mass BH populations with ≲104-6 M ⊙. We provide an estimate of the TDE rate over z = 4-11, associated with the properties of JWST-detected AGN host galaxies, and we find that deep and wide survey programs with JWST and the Roman Space Telescope (RST) can detect and identify TDEs up to z ≃ 4-7. The predicted detection numbers of TDEs at z > 4 in 1 yr are N TDE ∼ 2 - 10 ( 0.2 - 2 ) for the JADES-Medium (and COSMOS-Web) survey with JWST and N TDE ∼ 2 - 10 ( 8 - 50 ) for the deep (and wide) tiers of the High Latitude Time Domain Survey with RST. We further discuss survey strategies for hunting for transient high-redshift TDEs in wide-field surveys with RST, as well as a joint observation campaign with the Vera C. Rubin Observatory for enhancing the detection number. The high-redshift TDE search will give us a unique opportunity to probe the mass distribution of early BH populations.

    DOI

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    2
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  • Observational properties of active galactic nucleus obscuration during the peak of accretion growth

    Bovornpratch Vijarnwannaluk, Masayuki Akiyama, Malte Schramm, Yoshihiro Ueda, Yoshiki Matsuoka, Yoshiki Toba, Naoki Matsumoto, Angel Ruiz, Ioannis Georgantopoulos, Ektoras Pouliasis, Elias Koulouridis, Kohei Ichikawa, Marcin Sawicki, Stephen Gwyn

    Monthly Notices of the Royal Astronomical Society   529 ( 4 ) 3610 - 3629  2024.04  [Refereed]

     View Summary

    We investigated the gas obscuration and host galaxy properties of active galactic nuclei (AGNs) during the peak of cosmic accretion growth of supermassive black holes at redshift 0.8-1.8 using X-ray-detected AGNs with mid-infrared and far-infrared detection. The sample was classified as type-1 and type-2 AGNs using optical spectral and morphological classification while the host galaxy properties were estimated with multiwavelength spectral energy distribution fitting. For type-1 AGNs, the black hole mass was determined from MgII emission lines while the black hole mass of type-2 AGNs was inferred from the host galaxy's stellar mass. Based on the derived parameters, the distribution of the sample in the absorption hydrogen column density (NH) versus Eddington ratio diagram is examined. Among the type-2 AGNs, 28 ± 5 per cent are in the forbidden zone, where the obscuration by dust torus cannot be maintained due to radiation pressure on dusty material. The fraction is higher than that observed in the local universe from the Burst Alert Telescope AGN Spectroscopic Survey data release 2 (BASS DR2) (11 ± 3 per cent). The higher fraction implies that the obscuration of the majority of AGNs is consistent with the radiation pressure regulated unified model but with an increased incidence of interstellar matter (ISM)-obscured AGNs. We discuss the possibility of dust-free absorption in type-1 AGNs and heavy ISM absorption in type-2 AGNs. We also find no statistical difference in the star-formation activity between type-1 and type-2 AGNs which may suggest that obscuration triggered by a gas-rich merging is not common among X-ray detected AGNs in this epoch.

    DOI

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    3
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  • [O iv]- and [Ne v]-weak Active Galactic Nuclei Hidden by Compton-thick Material in Late Mergers

    Satoshi Yamada, Yoshihiro Ueda, Taiki Kawamuro, Claudio Ricci, Yoshiki Toba, Masatoshi Imanishi, Takamitsu Miyaji, Atsushi Tanimoto, Kohei Ichikawa, Martín Herrera-Endoqui, Shoji Ogawa, Ryosuke Uematsu, Keiichi Wada

    Astrophysical Journal   965 ( 2 )  2024.04  [Refereed]

     View Summary

    We study “buried” active galactic nuclei (AGNs) almost fully covered by circumnuclear material in ultra/luminous infrared galaxies (U/LIRGs), which show weak ionized lines from narrow-line regions. Employing an indicator of a [O iv] 25.89 or [Ne v] 14.32 μm line to 12 μm AGN luminosity ratio, we find 17 buried AGN candidates that are [O iv]-weak (L [O IV]/L 12,AGN ≤ −3.0) or [Ne v]-weak (L [Ne V]/L 12,AGN ≤ −3.4) among 30 AGNs in local U/LIRGs. For the [O iv]-weak AGNs, we estimate their covering fractions of Compton-thick (CT; N H ≥ 1024 cm−2) material with an X-ray clumpy torus model to be f CT ( spec ) = 0.55 ± 0.19 on average. This value is consistent with the fraction of CT AGNs ( f CT ( stat ) = 53 % ± 12 % ) among the [O iv]-weak AGNs in U/LIRGs and much larger than that in Swift/Burst Alert Telescope (BAT) AGNs (23% ± 6%). The fraction of [O iv]-weak AGNs increases from 27 − 10 + 13 % (early) to 66 − 12 + 10 % (late mergers). Similar results are obtained with the [Ne v] line. The [O iv]- or [Ne v]-weak AGNs in late mergers show larger N H and Eddington ratios (λ Edd) than those of the Swift/BAT AGNs, and the largest N H is ≳1025 cm−2 at log λ Edd ∼ − 1 , close to the effective Eddington limit for CT material. These suggest that (1) the circumnuclear material in buried AGNs is regulated by the radiation force from high-λ Edd AGNs on the CT obscurers, and (2) their dense material with large f CT ( spec ) (∼0.5 ± 0.1) in U/LIRGs is a likely cause of a unique structure of buried AGNs, whose amount of material may be maintained through merger-induced supply from their host galaxies.

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  • Deconvolution of JWST/MIRI Images: Applications to an Active Galactic Nucleus Model and GATOS Observations of NGC 5728

    M. T. Leist, C. Packham, D. J.V. Rosario, D. A. Hope, A. Alonso-Herrero, E. K.S. Hicks, S. Hönig, L. Zhang, R. Davies, T. Díaz-Santos, O. González-Martín, E. Bellocchi, P. G. Boorman, F. Combes, I. García-Bernete, S. García-Burillo, B. García-Lorenzo, H. Haidar, K. Ichikawa, M. Imanishi, S. M. Jefferies, Labiano, N. A. Levenson, R. Nikutta, M. Pereira-Santaella, C. Ramos Almeida, C. Ricci, D. Rigopoulou, W. Schaefer, M. Stalevski, M. J. Ward, L. Fuller, T. Izumi, D. Rouan, T. Shimizu

    Astronomical Journal   167 ( 3 )  2024.03  [Refereed]

     View Summary

    The superb image quality, stability, and sensitivity of JWST permit deconvolution techniques to be pursued with a fidelity unavailable to ground-based observations. We present an assessment of several deconvolution approaches to improve image quality and mitigate the effects of the complex JWST point-spread function (PSF). The optimal deconvolution method is determined by using WebbPSF to simulate JWST’s complex PSF and MIRISim to simulate multiband JWST/Mid-Infrared Imager Module (MIRIM) observations of a toy model of an active galactic nucleus (AGN). Five different deconvolution algorithms are tested: (1) Kraken deconvolution, (2) Richardson–Lucy, (3) the adaptive imaging deconvolution algorithm, (4) sparse regularization with the Condat–Vũ algorithm, and (5) iterative Wiener filtering and thresholding. We find that Kraken affords the greatest FWHM reduction of the nuclear source of our MIRISim observations for the toy AGN model while retaining good photometric integrity across all simulated wave bands. Applying Kraken to Galactic Activity, Torus, and Outflow Survey (GATOS) multiband JWST/MIRIM observations of the Seyfert 2 galaxy NGC 5728, we find that the algorithm reduces the FWHM of the nuclear source by a factor of 1.6–2.2 across all five filters. Kraken images facilitate detection of extended nuclear emission ∼2 5 (∼470 pc, position angle; 115°) in the SE–NW direction, especially at the longest wavelengths. We demonstrate that Kraken is a powerful tool to enhance faint features otherwise hidden in the complex JWST PSF.

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  • 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   962 ( 2 )  2024.02  [Refereed]

     View Summary

    We investigate the black hole mass function (BHMF) and Eddington-ratio distribution function (ERDF) of broad-line active galactic nuclei (AGNs) at z = 4, based on a sample of 52 quasars with i < 23.2 at 3.50 ≤ z ≤ 4.25 from the Hyper Suprime-Cam Subaru Strategic Program S16A-Wide2 data set, and 1462 quasars with i < 20.2 in the same redshift range from the Sloan Digital Sky Survey data release 7 quasar catalog. Virial black hole (BH) masses of quasars are estimated using the width of the CIV 1549 Å line and the continuum luminosity at 1350 Å. To obtain the intrinsic broad-line AGN BHMF and ERDF, we correct for the incompleteness in the low-mass and/or low-Eddington-ratio ranges caused by the flux-limited selection. The resulting BHMF is constrained down to log M BH / M ⊙ ∼ 7.5 . In comparison with broad-line AGN BHMFs at z ∼ 2 in the literature, we find that the number density of massive SMBHs peaks at higher redshifts, consistent with the downsizing evolutionary scenario. Additionally, the resulting ERDF shows a negative dependence on BH mass, suggesting more massive SMBHs tend to accrete at lower-Eddington ratios at z = 4. With the derived intrinsic broad-line AGN BHMF, we also evaluate the active fraction of broad-line AGNs among the entire SMBH population at z = 4. The resulting active fraction may suggest a positive dependence on BH mass. Finally, we examine the time evolution of broad-line AGN BHMF between z = 4 and 6 through solving the continuity equation. The results suggest that the broad-line AGN BHMFs at z = 4-6 only show evolution in their normalization, but with no significant changes in their shape.

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  • 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  [Refereed]

     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

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  • 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  [Refereed]

     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.

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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  [Refereed]

     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.

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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  [Refereed]

     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.

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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   11 ( 4 ) 504 - 513  2023.10  [Refereed]

    Authorship:Corresponding author

     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.

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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  [Refereed]

     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.

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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.

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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.

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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]

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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]

     View Summary

    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]

     View Summary

    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]

     View Summary

    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]

     View Summary

    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]

     View Summary

    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]

     View Summary

    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]

     View Summary

    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]

     View Summary

    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]

     View Summary

    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]

     View Summary

    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]

     View Summary

    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]

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    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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    13
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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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    9
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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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  • 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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  • 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

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    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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    15
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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]

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    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]

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    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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    19
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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]

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    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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    19
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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]

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    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]

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    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 />...