<title>Abstract</title>We present ALMA detection of the [O <sc>iii</sc>] 88 <italic>μ</italic>m line and 850 <italic>μ</italic>m dust continuum emission in a <italic>Y</italic>-dropout Lyman break galaxy, MACS0416_Y1. The [O <sc>iii</sc>] detection confirms the object with a spectroscopic redshift to be <italic>z</italic> = 8.3118±0.0003. The 850 <italic>μ</italic>m continuum intensity (0.14 mJy) implies a large dust mass on the order of 4×10⁶<italic>M</italic>_⊙. The ultraviolet-to-far infrared spectral energy distribution modeling, where the [O <sc>iii</sc>] emissivity model is incorporated, suggests the presence of a young (τ_age ≍ 4 Myr), star-forming (SFR ≍ 60<italic>M</italic>_⊙yr⁻¹), and moderately metal-polluted (<italic>Z</italic> ≍ 0.2<italic>Z</italic>_⊙) stellar component with a stellar mass of 3 × 10⁸<italic>M</italic>_⊙. An analytic dust mass evolution model with a single episode of star formation does not reproduce the metallicity and dust mass in ≍ 4 Myr, suggesting an underlying evolved stellar component as the origin of the dust mass.

We present the Atacama Large Millimeter/submillimeter Array (ALMA) detection
of the [O III] 88 $\mu$m line and rest-frame 90 $\mu$m dust continuum emission
in a Y-dropout Lyman break galaxy (LBG), MACS0416_Y1, lying behind the Frontier
Field cluster MACS J0416.1-2403. This [O III] detection confirms the LBG with a
spectroscopic redshift of $z = 8.3118 \pm 0.0003$, making this object one of
the furthest galaxies ever identified spectroscopically. The observed 850
$\mu$m flux density of $137 \pm 26$ $\mu$Jy corresponds to a de-lensed total
infrared (IR) luminosity of $L_{\rm IR} = (1.7 \pm 0.3) \times 10^{11}
L_{\odot}$ if assuming a dust temperature of $T_{\rm dust} = 50$ K and an
emissivity index of $\beta = 1.5$, yielding a large dust mass of $4 \times 10^6
M_{\odot}$. The ultraviolet-to-far IR spectral energy distribution modeling
where the [O III] emissivity model is incorporated suggests the presence of a
young ($\tau_{\rm age} \approx 4$ Myr), star-forming (SFR $\approx 60
M_{\odot}$ yr$^{-1}$), moderately metal-polluted ($Z \approx 0.2 Z_{\odot}$)
stellar component with a mass of $M_{\rm star} = 3 \times 10^8 M_{\odot}$. An
analytic dust mass evolution model with a single episode of star-formation does
not reproduce the metallicity and dust mass in $\tau_{\rm age} \approx 4$ Myr,
suggesting a pre-existing evolved stellar component with $M_{\rm star} \sim 3
\times 10^9 M_{\odot}$ and $\tau_{\rm age} \sim 0.3$ Gyr as the origin of the
dust mass.

We present new ALMA observations and physical properties of a Lyman Break
Galaxy at z=7.15. Our target, B14-65666, has a bright ultra-violet (UV)
absolute magnitude, $M_{\rm UV}\approx-22.4$, and has been spectroscopically
identified in Ly$\alpha$ with a small rest-frame equivalent width of $\approx4$
\AA. Previous HST image has shown that the target is comprised of two spatially
separated clumps in the rest-frame UV. With ALMA, we have newly detected
spatially resolved [OIII] 88 $\mu$m, [CII] 158 $\mu$m, and their underlying
dust continuum emission. In the whole system of B14-65666, the [OIII] and [CII]
lines have consistent redshifts of $7.1520\pm0.0003$, and the [OIII]
luminosity, $(34.4\pm4.1)\times10^{8}L_{\rm \odot}$, is about three times
higher than the [CII] luminosity, $(11.0\pm1.4)\times10^{8}L_{\rm \odot}$. With
our two continuum flux densities, the dust temperature is constrained to be
$T_{\rm d}\approx50-60$ K under the assumption of the dust emissivity index of
$\beta_{\rm d}=2.0-1.5$, leading to a large total infrared luminosity of
$L_{\rm TIR}\approx1\times10^{12}L_{\rm \odot}$. Owing to our high spatial
resolution data, we show that the [OIII] and [CII] emission can be spatially
decomposed into two clumps associated with the two rest-frame UV clumps whose
spectra are kinematically separated by $\approx200$ km s$^{-1}$. We also find
these two clumps have comparable UV, infrared, [OIII], and [CII] luminosities.
Based on these results, we argue that B14-65666 is a starburst galaxy induced
by a major-merger. The merger interpretation is also supported by the large
specific star-formation rate (defined as the star-formation rate per unit
stellar mass), sSFR$=260^{+119}_{-57}$ Gyr$^{-1}$, inferred from our SED
fitting. Probably, a strong UV radiation field caused by intense star formation
contributes to its high dust temperature and the [OIII]-to-[CII] luminosity
ratio.

A fundamental quest of modern astronomy is to locate the earliest galaxies
and study how they influenced the intergalactic medium a few hundred million
years after the Big Bang. The abundance of star-forming galaxies is known to
decline from redshifts of about 6 to 10, but a key question is the extent of
star formation at even earlier times, corresponding to the period when the
first galaxies might have emerged. Here we present spectroscopic observations
of MACS1149-JD1, a gravitationally lensed galaxy observed when the Universe was
less than four per cent of its present age. We detect an emission line of
doubly ionized oxygen at a redshift of $9.1096\pm0.0006$, with an uncertainty
of one standard deviation. This precisely determined redshift indicates that
the red rest-frame optical colour arises from a dominant stellar component that
formed about 250 million years after the Big Bang, corresponding to a redshift
of about 15. Our results indicate the it may be possible to detect such early
episodes of star formation in similar galaxies with future telescopes.

The physical properties and elemental abundances of the interstellar medium
in galaxies during cosmic reionization are important for understanding the role
of galaxies in this process. We report the Atacama Large
Millimeter/submillimeter Array detection of an oxygen emission line at a
wavelength of 88 micrometers from a galaxy at an epoch about 700 million years
after the Big Bang. The oxygen abundance of this galaxy is estimated at about
one-tenth that of the Sun. The non-detection of far-infrared continuum emission
indicates a deficiency of interstellar dust in the galaxy. A carbon emission
line at a wavelength of 158 micrometers is also not detected, implying an
unusually small amount of neutral gas. These properties might allow ionizing
photons to escape into the intergalactic medium.

We present an updated version of the so-called Madau model for attenuation of the radiation from distant objects by intergalactic neutral hydrogen. First, we derive the distribution function of intergalactic absorbers from the latest observational statistics of the Ly alpha forest, Lyman-limit systems and damped Ly alpha systems. The distribution function reproduces the observed redshift evolution of the Ly alpha depression and the mean-free path of the Lyman continuum excellently and simultaneously. We then derive a set of analytic functions describing the mean intergalactic attenuation curve for objects at z &gt; 0.5. The new model predicts less (or more) Ly alpha attenuation for z a parts per thousand integral 3-5 (z &gt; 6) sources through the usual broad-band filters relative to the original Madau model. This may cause a systematic difference in the photometric redshift estimates, which is, however, still small: about 0.05. Finally, we find a more than 0.5 mag overestimation of Lyman-continuum attenuation in the original Madau model at z &gt; 3, which causes a significant overcorrection against direct observations of the Lyman continuum of galaxies.

We investigate the potential use of nebular emission lines in the rest-frame
far-infrared (FIR) for determining spectroscopic redshift of z>8 galaxies with
the Atacama Large Millimeter/sub-millimeter Array (ALMA). After making a line
emissivity model as a function of metallicity, especially for the [O III] 88
micron line which is likely to be the strongest FIR line from H II regions, we
predict the line fluxes from high-z galaxies based on a cosmological
hydrodynamics simulation of galaxy formation. Since the metallicity of galaxies
reaches at ~0.2 Zsun even at z>8 in our simulation, we expect the [O III] 88
micron line as strong as 1.3 mJy for 27 AB objects, which is detectable at a
high significance by <1 hour integration with ALMA. Therefore, the [O III] 88
micron line would be the best tool to confirm the spectroscopic redshifts
beyond z=8.

Finding the first generation of galaxies in the early Universe is the greatest step forward towards understanding galaxy formation and evolution. For a strategic survey of such galaxies and the interpretation of the obtained data, this paper presents an ultraviolet-to-optical spectral model of galaxies with a great care of the nebular emission. In particular, we present a machinereadable table of intensities of 119 nebular emission lines from Ly alpha to the rest-frame 1 mu m as a function of metallicity from zero to the solar one. Based on the spectral model, we present criteria of equivalent widths of Ly alpha, He II lambda 1640, H alpha, H beta and [OIII]lambda 5007 to select extremely metal-poor and metal-free galaxies although these criteria have uncertainty caused by the Lyman continuum escape fraction and the star formation duration. We also present criteria of broad-band colours which will be useful to select candidates for spectroscopic follow-up from drop-out galaxies. We propose the line intensity ratio of [OIII]lambda 5007 to H beta &lt; 0.1 as the most robust criterion for &lt; 1/1000 of the solar metallicity. This ratio of a galaxy with a few M(circle dot)yr(-1) at z similar to 8 is detectable by spectroscopy with the James Webb Space Telescope within a reasonable exposure time.

The origin of cosmic dust is a fundamental issue in planetary science. This paper revisits the origin of dust in galaxies, in particular, in the Milky Way, by using a chemical evolution model of a galaxy composed of stars, interstellar medium, metals (elements heavier than helium), and dust. We start from a review of time-evolutionary equations of the four components, and then, we present simple recipes for the stellar remnant mass and yields of metal and dust based on models of stellar nucleosynthesis and dust formation. After calibrating some model parameters with the data from the solar neighborhood, we have confirmed a shortage of the stellar-dust-production rate relative to the dust-destruction rate by supernovae if the destruction efficiency suggested by theoretical works is correct. If the dust-mass growth by material accretion in molecular clouds is active, the observed dust amount in the solar neighborhood is reproduced. We present a clear analytic explanation of the mechanism for determining dust content in galaxies after the activation of accretion growth: a balance between accretion growth and supernova destruction. Thus, the dust content is independent of the uncertainty of the stellar dust yield after the growth activation. The timing of the activation is determined by a critical metal mass fraction which depends on the growth and destruction efficiencies. The solar system formation seems to have occurred well after the activation and plenty of dust would have existed in the proto-solar nebula.

Coronagraphic imaging for the Herbig Ae star, HD 142527, was performed using the Coronagraphic Imager with Adaptive Optics (CIAO) on the 8.2 m Subaru Telescope. The images were obtained in the H(2)O ice filter (lambda = 3.08 mu m) using adaptive optics (AO), and in the L&apos; band without AO. Combining these data with previous observational results in the H and K bands, we derived the spectra of the scattered light from the circumstellar disk around HD 142527 and detected an H2O ice absorption feature in the spectra. This result can be explained by the presence of silicate and H(2)O ice grains of similar to 1 mu m in size, according to the prediction model by Inoue et al. This grain size is consistent with previous observational study by Fukagawa et al. and Fujiwara et al. The present result demonstrates that high-resolution imaging of disk-scattered light in the ice band is useful for detecting H(2)O ice grain distributions in circumstellar disks.

The escape fraction of ionizing photons from galaxies is a crucial quantity controlling the cosmic ionizing background radiation and the reionization. Various estimates of this parameter can be obtained in the redshift range z = 0-6, either from direct observations or from the observed ionizing background intensities. We compare them homogeneously in terms of the observed flux density ratio of ionizing (similar to 900 angstrom rest-frame) to non-ionizing ultraviolet (similar to 1500 angstrom rest-frame) corrected for the intergalactic absorption. The escape fraction is found to increase by an order of magnitude, from a value less than 0.01 at z less than or similar to 1 to about 0.1 at z greater than or similar to 4.

We construct a new algorithm for estimating the star-formation rate (SFR) of galaxies from their infrared (IR) luminosity by developing the theory of the IR emission from a dusty H II region. The derived formula is SFR/(M-circle dot, yr(-1)) = [3.3 x 10(-10)(1 -eta)/(0.4 - 0.2f + 0.6 epsilon)](L-IR(obs)/L-circle dot), where f is the fraction of ionizing photons absorbed by hydrogen, epsilon is the efficiency of dust absorption for nonionizing photons from OB stars, and eta is the cirrus fraction of observed IR luminosity. The previous conversion formulae of SFR from the IR luminosity are applicable to only the case where the observed IR luminosity is nearly equal to the bolometric luminosity (starburst galaxies etc.), except for some empirical formulae. On the other hand, our theoretical SFR is applicable to galaxies even with a moderate star-formation activity. That is, our simple and convenient formula is significantly useful for estimating the SFR of various morphologies and types of galaxies - from early elliptical to late spiral and irregular galaxies, or from active starburst to quiescent galaxies - as long as they have neither an abnormal dust-to-gas ratio nor an evident active galactic nucleus.

ABSTRACT

We present the analysis of three intermediate-mass quiescent galaxies (QGs) with stellar masses of ${\sim} 10^{10}\, \mathrm{M}_{\odot }$ at redshifts $z\sim 3\!-\!4$ using NIRSpec low-resolution spectroscopy. Utilizing the spectral energy distribution fitting code bagpipes, we confirm these target galaxies are consistent with quiescent population, with their specific star formation rates falling below 2 dex the star-forming main sequence at the same redshifts. Additionally, we identify these QGs to be less massive than those discovered in previous works, particularly prior to the JWST era. Two of our target galaxies exhibit the potentially blended $\mathrm{ H} \, {\alpha }$ + [N ii] emission line within their spectra with signal-to-noise ratio ${\gt} 5$. We discuss whether this feature comes from an active galactic nucleus (AGN) or star formation, although future high-resolution spectroscopy is required to reach a conclusion. One of the target galaxies is covered by JWST/NIRCam imaging of the Public Release IMaging for Extragalactic Research survey. Using the 2D profile fitting code galfit, we examine its morphology, revealing a disc-like profile with a Sérsic index of $n=1.1 \pm 0.1$. On the size–mass relation, we find a potential distinction between less massive ($\log _{10}{(M_*/\mathrm{M}_\odot)}\lt 10.3$) and massive ($\log _{10}{(M_*/\mathrm{M}_\odot)}\gt 10.3$) QGs in their evolutionary pathways. The derived quenching time-scales for our targets are less than $1 \, {\rm Gyr}$. This may result from these galaxies being quenched by AGN feedback, supporting the AGN scenario of the emission line features.

The Cosmic Gems arc is among the brightest and highly magnified galaxies observed at redshift z ≈ 10.2 (ref. 1). However, it is an intrinsically ultraviolet faint galaxy, in the range of those now thought to drive the reionization of the Universe2–4. Hitherto the smallest features resolved in a galaxy at a comparable redshift are between a few hundreds and a few tens of parsecs (pc)5,6. Here we report JWST observations of the Cosmic Gems. The light of the galaxy is resolved into five star clusters located in a region smaller than 70 pc. They exhibit minimal dust attenuation and low metallicity, ages younger than 50 Myr and intrinsic masses of about 106M⊙. Their lensing-corrected sizes are approximately 1 pc, resulting in stellar surface densities near 105M⊙ pc−2, three orders of magnitude higher than typical young star clusters in the local Universe7. Despite the uncertainties inherent to the lensing model, they are consistent with being gravitationally bound stellar systems, that is, proto-globular clusters. We conclude that star cluster formation and feedback likely contributed to shaping the properties of galaxies during the epoch of reionization.

We present Atacama Large Millimetre/submillimetre Array (ALMA) observations of the [O iii] 88 emission of a sample of thirteen galaxies at to 7.6 selected as [C ii]-emitting companion sources of quasars. To disentangle the origins of the luminous Oxygen line in the Universe, we looked at emission-line galaxies that are selected through an excellent star-formation tracer [C ii] with star-formation rates between 9 and 162. Direct observations reveal [O iii] emission in just a single galaxy (), and a stacked image shows no [O iii] detection, providing deep upper limits on the ratios in the Universe (at). While the fidelity of this sample is high, no obvious optical/near-infrared counterpart is seen in the JWST imaging available for four galaxies. Additionally accounting for low-z CO emitters, line stacking shows that our sample-wide result remains robust: The enhanced reported in the first billion years of the Universe is likely due to the selection towards bright, blue Lyman-break galaxies with high surface star-formation rates or young stellar populations. The deep upper limit on the rest-frame 90 μm continuum emission (Jy at), implies a low average dust temperature (K) and high-dust mass (). As more normal galaxies are explored in the early Universe, synergy between JWST and ALMA is fundamental to further investigate the ISM properties of the a broad range of samples of high-z galaxies.

We present results of [C II] 158 μm emission line observations, and report the spectroscopic redshift confirmation of a strongly lensed (μ ∼ 20) star-forming galaxy, MACS0308-zD1 at z = 6.2078 ± 0.0002. The [C II] emission line is detected with a signal-to-noise ratio >6 within the rest-frame UV-bright clump of the lensed galaxy (zD1.1) and exhibits multiple velocity components; the narrow [C II] has a velocity full width half maximum (FWHM) of 110 ± 20 km s−1, while broader [C II] is seen with an FWHM of 230 ± 50 km s−1. The broader [C II] component is blueshifted (−80 ± 20 km s−1) with respect to the narrow [C II] component, and has a morphology that extends beyond the UV-bright clump. We find that, while the narrow [C II] emission is most likely associated with zD1.1, the broader component is possibly associated with a physically distinct gas component from zD1.1 (e.g., outflowing or inflowing gas). Based on the nondetection of λ158μm dust continuum, we find that MACS0308-zDl's star formation activity occurs in a dust-free environment indicated by a strong upper limit of infrared luminosity ≲9 × 108 Le. Targeting this strongly lensed faint galaxy for follow-up Atacama Large Millimeter/submillimeter Array and JWST observations will be crucial to characterize the details of typical galaxy growth in the early Universe.

Unveiling the emergence and prevalence of massive/bright galaxies during the epoch of reionization and beyond, within the first 600 million years of the Universe, stands as a pivotal pursuit in astronomy. Remarkable progress has been made by JWST in identifying an immense population of bright galaxies, which hints at exceptionally efficient galaxy assembly processes. However, the underlying physical mechanisms propelling their rapid growth remain unclear. With this in mind, millimeter and submillimeter-wave spectroscopic observations of redshifted far-infrared spectral lines, particularly the [O iii] 88 µm and [C ii] 158 µm lines, offers a crucial pathway to address this fundamental query. To this end, we develop a dual-polarization sideband-separating superconductor-insulator-superconductor (SIS) mixer receiver, FINER, for the Large Millimeter Telescope (LMT) situated in Mexico. Harnessing advancements from ALMA's wideband sensitivity upgrade (WSU) technology, FINER covers radio frequencies spanning 120-360 GHz, delivering an instantaneous intermediate frequency (IF) of 3-21 GHz per sideband per polarization, which is followed by a set of 10.24 GHz-wide digital spectrometers. At 40% of ALMA's light-collecting area, the LMT's similar atmospheric transmittance and FINER's 5 times wider bandwidth compared to ALMA culminate in an unparalleled spectral scanning capability in the northern hemisphere, paving the way for finer spectral-resolution detection of distant galaxies.

The protoclusters in the epoch of reionization, traced by galaxy overdensity regions, are ideal laboratories for studying the process of stellar assembly and cosmic reionization. We present the spectroscopic confirmation of the core of the most distant protocluster at z = 7.88, A2744-z7p9OD, with the James Webb Space Telescope NIRSpec integral field unit spectroscopy. The core region includes as many as four galaxies detected in [O iii] 4960 and 5008 Å in a small area of ∼3″ × 3″, corresponding to ∼11 × 11 kpc, after the lensing magnification correction. Three member galaxies are also tentatively detected in dust continuum in Atacama Large Millimeter/submillimeter Array Band 6, which is consistent with their red ultraviolet continuum slopes, β ∼ −1.3. The member galaxies have stellar masses in the range of log(M */M ⊙) ∼7.6-9.2 and star formation rates of ∼3-50 M ⊙ yr−1, showing a diversity in their properties. FirstLight cosmological simulations reproduce the physical properties of the member galaxies including the stellar mass, [O iii] luminosity, and dust-to-stellar mass ratio, and predict that the member galaxies are on the verge of merging in a few to several tens of Myr to become a large galaxy with M * ∼ 6 × 109 M ⊙. The presence of a multiple merger and evolved galaxies in the core region of A2744-z7p9OD indicates that environmental effects are already at work 650 Myr after the Big Bang.

Abstract

We present 20,567 Lyα emitters (LAEs) at z = 2.2 − 7.3 that are photometrically identified by the SILVERRUSH program in a large survey area up to 25 deg² with deep images of five broadband filters (grizy) and seven narrowband filters targeting Lyα lines at z = 2.2, 3.3, 4.9, 5.7, 6.6, 7.0, and 7.3 taken by the Hyper Suprime-Cam Subaru Strategic Program and the Cosmic HydrOgen Reionization Unveiled with Subaru survey. We select secure &gt;5σ sources showing narrowband color excesses via Lyα break screening, taking into account the spatial inhomogeneity of limiting magnitudes. After removing spurious sources by careful masking and visual inspection of coadded and multiepoch images obtained over the 7 yr of the surveys, we construct LAE samples consisting of 6995, 4641, 726, 6124, 2058, 18, and 5 LAEs at z = 2.2, 3.3, 4.9, 5.7, 6.6, 7.0, and 7.3, respectively, although the z = 7.3 candidates are tentative. Our LAE catalogs contain 289 spectroscopically confirmed LAEs at the expected redshifts from previous work. We demonstrate that the number counts of our LAEs are consistent with previous studies with similar LAE selection criteria. The LAE catalogs will be made public on our project webpage with detailed descriptions of the content and ancillary information about the masks and limiting magnitudes.

We report Atacama Large Millimeter/submillimeter Array Band 3 observations of CO(6−5), CO(7−6), and [C i](2−1) in B14-65666 (“Big Three Dragons”), one of the brightest Lyman-break galaxies at z > 7 in the rest-frame ultraviolet continuum, far-infrared continuum, and emission lines of [O iii] 88 μm and [C ii] 158 μm. CO(6−5), CO(7−6), and [C i](2−1), whose 3σ upper limits on the luminosities are approximately 40 times fainter than the [C ii] luminosity, are all not detected. The L [C II]/L CO(6-5) and L [C II]/L CO(7-6) ratios are higher than the typical ratios obtained in dusty star-forming galaxies or quasar host galaxies at similar redshifts, and they may suggest a lower gas density in the photodissociated region in B14-65666. By using the (1) [C ii] luminosity, (2) dust mass-to-gas mass ratio, and (3) a dynamical mass estimate, we find that the molecular gas mass (M mol) is (0.05-11) × 1010 M ⊙. This value is consistent with the upper limit inferred from the nondetection of mid-J CO and [C i](2−1). Despite the large uncertainty in M mol, we estimate a molecular gas-to-stellar mass ratio (μ gas) of 0.65-140 and a gas depletion time (τ dep) of 2.5-550 Myr; these values are broadly consistent with those of other high-redshift galaxies. B14-65666 could be an ancestor of a passive galaxy at z ≳ 4 if no gas is fueled from outside the galaxy.

Abstract

We present kinematics of six local extremely metal-poor galaxies (EMPGs) with low metallicities (0.016–0.098 Z_⊙) and low stellar masses (10^4.7–10^7.6M_⊙). Taking deep medium/high-resolution (R ∼ 7500) integral-field spectra with 8.2 m Subaru, we resolve the small inner velocity gradients and dispersions of the EMPGs with Hα emission. Carefully masking out substructures originating by inflow and/or outflow, we fit three-dimensional disk models to the observed Hα flux, velocity, and velocity dispersion maps. All the EMPGs show rotational velocities (v_rot) of 5–23 km s⁻¹ smaller than the velocity dispersions (σ₀) of 17–31 km s⁻¹, indicating dispersion-dominated (v_rot/σ₀ = 0.29–0.80 &lt; 1) systems affected by inflow and/or outflow. Except for two EMPGs with large uncertainties, we find that the EMPGs have very large gas-mass fractions of f_gas ≃ 0.9–1.0. Comparing our results with other Hα kinematics studies, we find that v_rot/σ₀ decreases and f_gas increases with decreasing metallicity, decreasing stellar mass, and increasing specific star formation rate. We also find that simulated high-z (z ∼ 7) forming galaxies have gas fractions and dynamics similar to the observed EMPGs. Our EMPG observations and the simulations suggest that primordial galaxies are gas-rich dispersion-dominated systems, which would be identified by the forthcoming James Webb Space Telescope observations at z ∼ 7.

We present the results of 300 pc resolution Atacama Large Millimeter/submillimeter Array imaging of the [O iii] 88 & mu;m line and dust continuum emission from a z = 8.312 Lyman-break galaxy MACS0416_Y1. The velocity-integrated [O iii] emission has three peaks that are likely associated with three young stellar clumps of MACS0416_Y1, while the channel map shows a complicated velocity structure with little indication of a global velocity gradient unlike what was found in [C ii] 158 & mu;m at a larger scale, suggesting random bulk motion of ionized gas clouds inside the galaxy. In contrast, dust emission appears as two individual clumps apparently separating or bridging the [O iii]/stellar clumps. The cross-correlation coefficient between dust and ultraviolet-related emission (i.e., [O iii] and ultraviolet continuum) is unity on a galactic scale, while it drops at <1 kpc, suggesting well-mixed geometry of multiphase interstellar media on subkiloparsec scales. If the cutoff scale characterizes different stages of star formation, the cutoff scale can be explained by gravitational instability of turbulent gas. We also report on a kiloparsec-scale off-center cavity embedded in the dust continuum image. This could be a superbubble producing galactic-scale outflows, since the energy injection from the 4 Myr starburst suggested by a spectral energy distribution analysis is large enough to push the surrounding media creating a kiloparsec-scale cavity.

ABSTRACT

Radio-loud active galactic nuclei (RLAGNs) are rare among AGN populations. Lacking high-resolution and high-frequency observations, their structure and evolution stages are not well understood at high redshifts. In this work, we report Atacama Large Millimeter/submillimeter Array 237 GHz continuum observation at 0.023 arcsec resolution and Very Large Array (VLA) 44 GHz continuum observation at 0.08 arcsec resolution of the radio continuum emission from a high-redshift radio and hyper-luminous infrared galaxy at z = 1.92. The new observations confirm the South-East (SE) and North-West (NW) hotspots identified by previous low-resolution VLA observations at 4.7 and 8.2 GHz and identify a radio core undetected in all previous observations. The SE hotspot has a higher flux density than the NW one does by a factor of 6, suggesting that there can be a Doppler boosting effect in the SE one. In this scenario, we estimate the advance speed of the jet head, ranging from ∼0.1c to 0.3c, which yields a mildly relativistic case. The projected linear distance between the two hotspots is ∼13 kpc, yielding a linear size (≤20 kpc) of a compact-steep-spectrum (CSS) source. Combined with new high-frequency (νobs ≥ 44 GHz) and archived low-frequency observations (νobs ≤ 8.2 GHz), we find that injection spectra of both NW and SE hotspots can be fitted with a continuous injection (CI) model. Based on the CI model, the synchrotron ages of NW and SE hotspots have an order of 105 yr, consistent with the order of magnitude 103–105 yr observed in CSS sources associated with radio AGNs at an early evolution stage. The CI model also favours the scenario in which the double hotspots have experienced a quiescent phase, suggesting that this RLAGN may have transient or intermittent activities.

We present integral field, far-infrared (FIR) spectroscopy of Mrk 54, a local Lyman continuum emitter, obtained with FIFI-LS on the Stratospheric Observatory for Infrared Astronomy. This is only the second time, after Haro 11, that [C ii] 158 mu m and [O iii] 88 mu m spectroscopy of the known LCEs have been obtained. We find that Mrk 54 has a strong [C ii] emission that accounts for similar to 1% of the total FIR luminosity, whereas it has only moderate [O iii] emission, resulting in the low [O iii]/[C ii] luminosity ratio of 0.22 +/- 0.06. In order to investigate whether [O iii]/[C ii] is a useful tracer of f (esc) (LyC escape fraction), we examine the correlations of [O iii]/[C ii] and (i) the optical line ratio of O-32 equivalent to [O iii] 5007 angstrom/[O ii] 3727 angstrom, (ii) specific star formation rate, (iii) [O iii] 88 mu m/[O i] 63 mu m ratio, (iv) gas-phase metallicity, and (v) dust temperature based on a combined sample of Mrk 54 and the literature data from the Herschel Dwarf Galaxy Survey and the LITTLE THINGS Survey. We find that galaxies with high [O iii]/[C ii] luminosity ratios could be the result of high ionization (traced by O-32), bursty star formation, high ionized-to-neutral gas volume filling factors (traced by [O iii] 88 mu m/[O i] 63 mu m), and low gas-phase metallicities, which is in agreement with theoretical predictions. We present an empirical relation between the [O iii]/[C ii] ratio and f (esc) based on the combination of the [O iii]/[C ii] and O-32 correlation, and the known relation between O-32 and f (esc). The relation implies that high-redshift galaxies with high [O iii]/[C ii] ratios revealed by the Atacama Large Millimeter/submillimeter Array may have f (esc) greater than or similar to 0.1, significantly contributing to the cosmic reionization.

Abstract

The primordial He abundance Y_P is a powerful probe of cosmology. Currently, Y_P is best determined by observations of metal-poor galaxies, while there are only a few known local extremely metal-poor (&lt;0.1Z_⊙) galaxies (EMPGs) having reliable He/H measurements with He iλ10830 near-infrared (NIR) emission. Here we present deep Subaru NIR spectroscopy for 10 EMPGs. Combining the existing optical data, He/H values of 5 out of the 10 EMPGs are reliably derived by the Markov chain Monte Carlo algorithm. Adding the existing 3 EMPGs and 51 moderately metal-poor (0.1–0.4Z_⊙) galaxies with reliable He/H estimates, we obtain ${Y}_{ { \rm{P } } }={0.2370}_{-0.0034}^{+0.0033}$ by linear regression in the (He/H) − (O/H) plane, where we increase the number of EMPGs from three to eight anchoring He/H of the most metal-poor gas in galaxies. Although our Y_P measurement and previous measurements are consistent, our result is slightly (∼1σ) smaller due to our EMPGs. Including the existing primordial deuterium D_P measurement, we constrain the effective number of neutrino species N_eff and the baryon-to-photon ratio η showing ≳1–2σ tensions with the Standard Model and Planck Collaboration et al. (2020). Motivated by the tensions, we allow the degeneracy parameter of the electron neutrino ξ_e, as well as N_eff and η, to vary. We obtain ${\xi }_{e}={0.05}_{-0.02}^{+0.03}$, ${N}_{\mathrm{eff } }={3.11}_{-0.31}^{+0.34}$, and $\eta \times {10}^{10}={6.08}_{-0.06}^{+0.06}$ from the Y_P and D_P measurements with a prior of η taken from Planck Collaboration et al. Our constraints suggest a lepton asymmetry and allow for a high value of N_eff within the 1σ level, which could mitigate the Hubble tension.

Abstract

We present our new Atacama Large Millimeter/submillimeter Array (ALMA) observations targeting CO(6–5) emission from three luminous Lyman-break galaxies (LBGs) at z_spec = 6.0293–6.2037 found in the Subaru/Hyper Suprime-Cam survey, whose [O iii] 88 μm and [C ii] 158 μm emissions have been detected with ALMA. We find a marginal detection of the CO(6–5) line from one of our LBGs, J0235–0532, at the ≃4σ significance level and obtain upper limits for the other two LBGs, J1211–0118 and J0217–0208. Our z = 6 luminous LBGs are consistent with the previously found correlation between the CO luminosity and the infrared luminosity. The unique ensemble of the multiple far-infrared emission lines and underlying continuum fed to a photodissociation region model reveals that J0235–0532 has a relatively high density of hydrogen nuclei n_H that is comparable to those of low-z (U)LIRGs, quasars, and Galactic star-forming regions with high n_H values, while the other two LBGs have lower n_H consistent with local star-forming galaxies. By carefully taking account of various uncertainties, we obtain constraints on total gas mass and gas surface density from their CO luminosity measurements. We find that J0235–0532 is located below the Kennicutt–Schmidt (KS) relation, comparable to the z = 5.7 LBG, HZ10, previously detected with CO(2–1). Combined with previous results for dusty starbursts at similar redshifts, the KS relation at z = 5–6 is on average consistent with the local one.

Abstract

We present photoionization modeling of galaxy populations at z ∼ 0, 2, and &gt;6 to bridge optical and far-infrared (FIR) emission-line diagrams. We collect galaxies with measurements of optical and/or FIR ([O iii] 88 μm and [C ii] 158 μm) emission-line fluxes and plot them on the [O iii]λ5007/Hβ–[N ii]λ6585/Hα (BPT) and L([O iii]₈₈)/SFR–L([C ii]₁₅₈)/SFR diagrams, where SFR is the star formation rate and L([O iii]₈₈) and L([C ii]₁₅₈) are the FIR line luminosities. We aim to explain the galaxy distributions on the two diagrams with photoionization models that employ three nebular parameters: the ionization parameter U, hydrogen density n_H, and gaseous metallicity Z_gas. Our models successfully reproduce the nebular parameters of local galaxies, and then predict the distributions of the z ∼ 0, 2, and &gt;6 galaxies in the diagrams. The predicted distributions illustrate the redshift evolution on all the diagrams; e.g., [O iii]/Hβ and [O iii]₈₈/[C ii]₁₅₈ ratios continuously decrease from z &gt; 6 to 0. Specifically, the z &gt; 6 galaxies exhibit ∼0.5 dex higher U than low-redshift galaxies at a given Z_gas and show predicted flat distributions on the BPT diagram at ${\rm{log } }[{\rm{O } }\,{\rm\small{III } }]/{\rm{H } }\beta \,=\,$ 0.5–0.8. We find that some of the z &gt; 6 galaxies exhibit high L([O iii]₈₈)/SFR ratios. To explain these high ratios, our photoionization models require a low stellar-to-gaseous-metallicity ratio or bursty/increasing star formation history at z &gt; 6. JWST will test the predictions and scenarios for the z &gt; 6 galaxies proposed by our photoionization modeling.

We present new observations with the Atacama Large Millimeter/submillimeter Array for a gravitationally lensed galaxy at z = 9.1, MACS1149-JD1. [O iii] 88 μm emission is detected at 10σ with a spatial resolution of 1/40.3 kpc in the source plane, enabling the most distant morphokinematic study of a galaxy. The [O iii] emission is distributed smoothly without any resolved clumps and shows a clear velocity gradient with "V obs/2σ tot = 0.84 ± 0.23, where "V obs is the observed maximum velocity difference and σ tot is the velocity dispersion measured in the spatially integrated line profile, suggesting a rotating system. Assuming a geometrically thin self-gravitating rotation disk model, we obtain Vrot/σV=0.67-0.26+0.73, where V rot and σ V are the rotation velocity and velocity dispersion, respectively, still consistent with rotation. The resulting disk mass of 0.65-0.40+1.37×109 M ⊙ is consistent with being associated with the stellar mass identified with a 300 Myr old stellar population independently indicated by a Balmer break in the spectral energy distribution. We conclude that the most of the dynamical mass is associated with the previously identified mature stellar population that formed at z ∼15.

We present spatially resolved morphological properties of [C II] 158 μm, [O III] 88 μm, dust, and rest-frame ultraviolet (UV) continuum emission for A1689-zD1, a strongly lensed, sub-L* galaxy at z = 7.13, by utilizing deep Atacama Large Millimeter/submillimeter Array (ALMA) and Hubble Space Telescope (HST) observations. While the [O III] line and UV continuum are compact, the [C II] line is extended up to a radius of r ∼ 12 kpc. Using multi-band rest-frame far-infrared continuum data ranging from 52 to 400 μm, we find an average dust temperature and emissivity index of T dust = 41 − 14 + 17 K and β = 1.7 − 0.7 + 1.1 , respectively, across the galaxy. We find slight differences in the dust continuum profiles at different wavelengths, which may indicate that the dust temperature decreases with distance. We map the star formation rate (SFR) via IR and UV luminosities and determine a total SFR of 37 ± 1M ⊙yr−1 with an obscured fraction of 87%. While the [O III] line is a good tracer of the SFR, the [C II] line shows deviation from the local L [C II]-SFR relations in the outskirts of the galaxy. Finally, we observe a clear difference in the line profile between [C II] and [O III], with significant residuals (∼5σ) in the [O III] line spectrum after subtracting a single Gaussian model. This suggests a possible origin of the extended [C II] structure from the cooling of hot ionized outflows. The extended [C II] and high-velocity [O III] emission may both contribute in part to the high L [O III]/L [C II] ratios recently reported in z > 6 galaxies.

<jats:title>Abstract</jats:title>
<jats:p>We conduct intensity mapping to probe for extended diffuse Ly<jats:italic>α</jats:italic> emission around Ly<jats:italic>α</jats:italic> emitters (LAEs) at <jats:italic>z</jats:italic> ∼2−7, exploiting very deep (∼26 mag at 5<jats:italic>σ</jats:italic>) and large-area (∼4.5 deg<jats:sup>2</jats:sup>) Subaru/Hyper Suprime-Cam narrowband (NB) images and large LAE catalogs consisting of a total of 1540 LAEs at <jats:italic>z</jats:italic> = 2.2, 3.3, 5.7, and 6.6 obtained by the HSC-SSP and CHORUS projects. We calculate the spatial correlations of these LAEs with ∼1–2 billion pixel flux values of the NB images, deriving the average Ly<jats:italic>α</jats:italic> surface brightness (SB<jats:sub>Ly<jats:italic>α</jats:italic>
</jats:sub>) radial profiles around the LAEs. By carefully estimating systematics such as fluctuations of sky background and point-spread functions, we detect Ly<jats:italic>α</jats:italic> emission at 100–1000 comoving kpc around <jats:italic>z</jats:italic> = 3.3 and 5.7 LAEs at the 3.2<jats:italic>σ</jats:italic> and 3.7<jats:italic>σ</jats:italic> levels, respectively, and tentatively (=2.0<jats:italic>σ</jats:italic>) at <jats:italic>z</jats:italic> = 6.6. The emission is as diffuse as ∼10<jats:sup>−20</jats:sup>–10<jats:sup>−19</jats:sup> erg s<jats:sup>−1</jats:sup> cm<jats:sup>−2</jats:sup> arcsec<jats:sup>−2</jats:sup> and extended beyond the virial radius of a dark matter halo with a mass of 10<jats:sup>11</jats:sup>
<jats:italic>M</jats:italic>
<jats:sub>⊙</jats:sub>. While the observed SB<jats:sub>Ly<jats:italic>α</jats:italic>
</jats:sub> profiles have similar amplitudes at <jats:italic>z</jats:italic> = 2.2–6.6 within the uncertainties, the intrinsic SB<jats:sub>Ly<jats:italic>α</jats:italic>
</jats:sub> profiles (corrected for the cosmological dimming effect) increase toward high redshifts. This trend may be explained by increasing hydrogen gas density due to the evolution of the cosmic volume. Comparisons with theoretical models suggest that extended Ly<jats:italic>α</jats:italic> emission around an LAE is powered by resonantly scattered Ly<jats:italic>α</jats:italic> photons in the CGM and IGM that originate from the inner part of the LAE and/or neighboring galaxies around the LAE.</jats:p>

Abstract

We present Keck/LRIS follow-up spectroscopy for 13 photometric candidates of extremely metal-poor galaxies (EMPGs) selected by a machine-learning technique applied to the deep (∼26 AB mag) optical and wide-area (∼500 deg²) Subaru imaging data in the EMPRESS survey. Nine out of the 13 candidates are EMPGs with an oxygen abundance (O/H) less than ∼10% solar value (O/H)_⊙, and four sources are contaminants of moderately metal-rich galaxies or no emission-line objects. Notably, two out of the nine EMPGs have extremely low stellar masses and oxygen abundances of 5 × 10⁴–7 × 10⁵M_⊙ and 2%–3% (O/H)_⊙, respectively. With a sample of five EMPGs with (Fe/O) measurements, two (three) of which are taken from this study (the literature), we confirm that two EMPGs with the lowest (O/H) ratios of ∼2% (O/H)_⊙ show high (Fe/O) ratios of ∼0.1, close to the solar abundance ratio. Comparing galaxy chemical enrichment models, we find that the two EMPGs cannot be explained by a scenario of metal-poor gas accretion/episodic star formation history due to their low (N/O) ratios. We conclude that the two EMPGs can be reproduced by the inclusion of bright hypernovae and/or hypothetical pair-instability supernovae (SNe) preferentially produced in a metal-poor environment. This conclusion implies that primordial galaxies at z ∼ 10 could have a high abundance of Fe that did not originate from Type Ia SNe with delays and that Fe may not serve as a cosmic clock for primordial galaxies.

We present the Swimmy (Subaru WIde-field Machine-learning anoMalY) survey program, a deep-learning-based search for unique sources using multicolored (grizy) imaging data from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). This program aims to detect unexpected, novel, and rare populations and phenomena, by utilizing the deep imaging data acquired from the wide-field coverage of the HSC-SSP. This article, as the first paper in the Swimmy series, describes an anomaly detection technique to select unique populations as "outliers"from the data-set. The model was tested with known extreme emission-line galaxies (XELGs) and quasars, which consequently confirmed that the proposed method successfully selected ∼60%-70% of the quasars and 60% of the XELGs without labeled training data. In reference to the spectral information of local galaxies at z = 0.05-0.2 obtained from the Sloan Digital Sky Survey, we investigated the physical properties of the selected anomalies and compared them based on the significance of their outlier values. The results revealed that XELGs constitute notable fractions of the most anomalous galaxies, and certain galaxies manifest unique morphological features. In summary, deep anomaly detection is an effective tool that can search rare objects, and, ultimately, unknown unknowns with large data-sets. Further development of the proposed model and selection process can promote the practical applications required to achieve specific scientific goals.

<title>Abstract</title>
Morphological studies are crucial to investigate the connections between active galactic nucleus (AGN) activities and the evolution of galaxies. Substantial studies have found that radiative-mode AGNs primarily reside in disk galaxies, questioning the merger-driven mechanism of AGN activities. In this study, through Sérsic profile fitting and nonparametric morphological parameter measurements, we investigated the morphology of host galaxies of 485 optical variability-selected low-luminosity AGNs at <italic>z</italic> ≲ 4.26 in the COSMOS field. We analyzed high-resolution images of the Hubble Space Telescope to measure these morphological parameters. We only successfully measured the morphological parameters for 76 objects and most AGN hosts (∼70%) were visually compact point-like sources. We examined the obtained morphological information as a function of redshift and compared them with literature data. We found that these AGN host galaxies showed no clear morphological preference. However, the merger rate increased with higher host star formation rate and AGN luminosity. Interestingly, we found ongoing star formation consistent with the typical star-forming populations in both elliptical and spiral galaxies, while these two types of galaxies were more symmetric than normal star-forming galaxies. These results suggest that optical variability-selected AGNs have higher probabilities to reside in elliptical galaxies than infrared-selected AGNs, whose host galaxies have a strong disk dominance, and support recent findings that the AGN feedback can enhance star-forming activities in host galaxies.

<title>ABSTRACT</title>
We present results from a new cosmological hydrodynamics simulation campaign of protocluster (PC) regions, FOREVER22: FORmation and EVolution of galaxies in Extremely overdense Regions motivated by SSA22. The simulations cover a wide range of cosmological scales using three different zoom set-ups in a parent volume of $(714.2~\rm cMpc)^{3}$: PCR (Proto-Cluster Region; V = (28.6 cMpc)3, SPH particle mass, mSPH = 4.1 × 106 M⊙, and final redshift, zend = 2.0), BCG (Brightest proto-Cluster Galaxy; V ∼ (10 cMpc)3, mSPH = 5.0 × 105 M⊙ and zend = 4.0), and First (V ∼ (3 cMpc)3, mSPH = 7.9 × 103 M⊙ and zend = 9.5) runs, that allow us to focus on different aspects of galaxy formation. In the PCR runs, we follow 10 PCs, each harbouring 1–4 SMBHs with ${\rm M_{\rm BH } }\ge 10^{9}~{\rm M_{\odot } }$. One of the PC cores shows a spatially close arrangement of seven starburst galaxies with ${\rm SFR} \gtrsim 100~{\rm {\rm M_{\odot } }~{\rm yr^{-1 } } }$ each, that are dust-obscured and would appear as submillimetre galaxies with flux ≳1 mJy at $1.1~ \rm mm$ in observations. The BCG runs show that the total SFRs of haloes hosting BCGs are affected by AGN feedback, but exceed $1000~{\rm {\rm M_{\odot } }~{\rm yr^{-1 } } }$ at z ≲ 6. The First runs resolve mini-haloes hosting population (Pop) III stars and we show that, in PC regions, the dominant stellar population changes from Pop III to Pop II at z ≳ 20, and the first galaxies with ${\rm SFR} \gtrsim 18~{\rm {\rm M_{\odot } }~{\rm yr^{-1 } } }$ form at z ∼ 10. These can be prime targets for future observations with the James Webb Space Telescope. Our simulations successfully reproduce the global star formation activities in observed PCs and suggest that PCs can kickstart cosmic reionization.

<title>Abstract</title>
We present new Atacama Large Millimeter/submillimeter Array Band 7 observational results of a Lyman-break galaxy at <italic>z</italic> = 7.15, B14-65666 (“Big Three Dragons”), which is an object detected in [O <sc>iii</sc>] 88 <italic>μ</italic>m, [C <sc>ii</sc>] 158 <italic>μ</italic>m, and dust continuum emission during the epoch of reionization. Our targets are the [N <sc>ii</sc>] 122 <italic>μ</italic>m fine-structure emission line and the underlying 120 <italic>μ</italic>m dust continuum. The dust continuum is detected with a ∼19<italic>σ</italic> significance. From far-infrared spectral energy distribution sampled at 90, 120, and 160 <italic>μ</italic>m, we obtain a best-fit dust temperature of 40 K (79 K) and an infrared luminosity of <inline-formula>
<tex-math>
<?CDATA ${\mathrm{log } }_{10}({L}_{\mathrm{IR } }/{L}_{\odot })=11.6$?>
</tex-math>
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:msub>
<mml:mrow>
<mml:mi>log</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>10</mml:mn>
</mml:mrow>
</mml:msub>
<mml:mo stretchy="false">(</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mi>L</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>IR</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mrow>
<mml:mo stretchy="true">/</mml:mo>
</mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>L</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mo>⊙</mml:mo>
</mml:mrow>
</mml:msub>
<mml:mo stretchy="false">)</mml:mo>
<mml:mo>=</mml:mo>
<mml:mn>11.6</mml:mn>
</mml:math>
<inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2a36ieqn1.gif" xlink:type="simple" />
</inline-formula> (12.1) at the emissivity index <italic>β</italic> = 2.0 (1.0). The [N <sc>ii</sc>] 122 <italic>μ</italic>m line is not detected. The 3<italic>σ</italic> upper limit of the [N <sc>ii</sc>] luminosity is 8.1 × 10⁷
<italic>L</italic>
_⊙. From the [N <sc>ii</sc>], [O <sc>iii</sc>], and [C <sc>ii</sc>] line luminosities, we use the Cloudy photoionization code to estimate nebular parameters as functions of metallicity. If the metallicity of the galaxy is high (<italic>Z</italic> &gt; 0.4 <italic>Z</italic>
_⊙), the ionization parameter and hydrogen density are <inline-formula>
<tex-math>
<?CDATA ${\mathrm{log } }_{10}U\simeq -2.7\pm 0.1$?>
</tex-math>
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:msub>
<mml:mrow>
<mml:mi>log</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mn>10</mml:mn>
</mml:mrow>
</mml:msub>
<mml:mi>U</mml:mi>
<mml:mo>≃</mml:mo>
<mml:mo>−</mml:mo>
<mml:mn>2.7</mml:mn>
<mml:mo>±</mml:mo>
<mml:mn>0.1</mml:mn>
</mml:math>
<inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac2a36ieqn2.gif" xlink:type="simple" />
</inline-formula> and <italic>n</italic>
_H ≃ 50–250 cm⁻³, respectively, which are comparable to those measured in low-redshift galaxies. The nitrogen-to-oxygen abundance ratio, N/O, is constrained to be subsolar. At <italic>Z</italic> &lt; 0.4 <italic>Z</italic>
_⊙, the allowed <italic>U</italic> drastically increases as the assumed metallicity decreases. For high ionization parameters, the N/O constraint becomes weak. Finally, our Cloudy models predict the location of B14-65666 on the BPT diagram, thereby allowing a comparison with low-redshift galaxies.

<title>Abstract</title>
The Ly<italic>α</italic> luminosity function (LF) of Ly<italic>α</italic> emitters (LAEs) has been used to constrain the neutral hydrogen fraction in the intergalactic medium (IGM) and thus the timeline of cosmic reionization. Here we present the results of a new narrowband imaging survey for <italic>z</italic> = 7.3 LAEs in a large area of ∼3 deg² with Subaru/Hyper Suprime-Cam. No LAEs are detected down to <italic>L</italic>
_{Ly<italic>α</italic>} ≃ 10^43.2 erg s⁻¹ in an effective cosmic volume of ∼2 × 10⁶ Mpc³, placing an upper limit on the bright part of the <italic>z</italic> = 7.3 Ly<italic>α</italic> LF for the first time and confirming a decrease in bright LAEs from <italic>z</italic> = 7.0. By comparing this upper limit with the Ly<italic>α</italic> LF in the case of fully ionized IGM, which is predicted using an observed <italic>z</italic> = 5.7 Ly<italic>α</italic> LF on the assumption that the intrinsic Ly<italic>α</italic> LF evolves in the same way as the UV LF, we obtain the relative IGM transmission <inline-formula>
<tex-math>
<?CDATA ${T}_{\mathrm{Ly}\alpha }^{\mathrm{IGM } }(7.3)/{T}_{\mathrm{Ly}\alpha }^{\mathrm{IGM } }(5.7)\lt 0.77$?>
</tex-math>
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll">
<mml:msubsup>
<mml:mrow>
<mml:mi>T</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>Ly</mml:mi>
<mml:mi>α</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>IGM</mml:mi>
</mml:mrow>
</mml:msubsup>
<mml:mo stretchy="false">(</mml:mo>
<mml:mn>7.3</mml:mn>
<mml:mo stretchy="false">)</mml:mo>
<mml:mrow>
<mml:mo stretchy="true">/</mml:mo>
</mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>T</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>Ly</mml:mi>
<mml:mi>α</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>IGM</mml:mi>
</mml:mrow>
</mml:msubsup>
<mml:mo stretchy="false">(</mml:mo>
<mml:mn>5.7</mml:mn>
<mml:mo stretchy="false">)</mml:mo>
<mml:mo>&lt;</mml:mo>
<mml:mn>0.77</mml:mn>
</mml:math>
<inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac308bieqn1.gif" xlink:type="simple" />
</inline-formula> and then the volume-averaged neutral fraction <italic>x</italic>
_{H I}(7.3) &gt; 0.28. Cosmic reionization is thus still ongoing at <italic>z</italic> = 7.3, consistent with results from other <italic>x</italic>
_{H I} estimation methods. A similar analysis using literature Ly<italic>α</italic> LFs finds that at <italic>z</italic> = 6.6 and 7.0, the observed Ly<italic>α</italic> LF agrees with the predicted one, consistent with full ionization.

Water ice has a strong spectral feature at a wavelength of approximately 3 mu m, which plays a vital role in our understanding of the icy universe. In this study, we investigate the scattering polarization of this water-ice feature. The linear polarization degree of light scattered by micron-sized icy grains is known to be enhanced at the ice band; however, the dependence of this polarization enhancement on various grain properties is unclear. We find that the enhanced polarization at the ice band is sensitive to the presence of micron-sized grains as well as their ice abundance. We demonstrate that this enhancement is caused by the high absorbency of the water-ice feature, which attenuates internal scattering and renders the surface reflection dominant over internal scattering. Additionally, we compare our models with polarimetric observations of the low-mass protostar L1551 IRS 5. Our results show that scattering by a maximum grain radius of a few microns with a low water-ice abundance is consistent with observations. Thus, scattering polarization of the water-ice feature is a useful tool for characterizing ice properties in various astronomical environments.

We present Atacama Large Millimeter/submillimeter Array [C ii] 158 μm line and far-infrared (FIR) continuum emission observations toward HSC J120505.09-000027.9 (J1205-0000) at z = 6.72 with a beam size of ∼0.″8 × 0.″5 (or 4.1 kpc × 2.6 kpc), the most distant red quasar known to date. Red quasars are modestly reddened by dust and are thought to be in rapid transition from an obscured starburst to an unobscured normal quasar, driven by powerful active galactic nucleus (AGN) feedback that blows out a cocoon of interstellar medium. The FIR continuum of J1205-0000 is bright, with an estimated luminosity of L FIR ∼ 3 × 1012 L o˙. The [C ii] line emission is extended on scales of r ∼ 5 kpc, greater than that of the FIR continuum. The line profiles at the extended regions are complex and broad (FWHM ∼ 630-780 km s-1). Although it is not practical to identify the nature of this extended structure, possible explanations include (i) companion/merging galaxies and (ii) massive AGN-driven outflows. For the case of (i), the companions are modestly star-forming (∼10 M o˙ yr-1) but are not detected by our Subaru optical observations (y AB,5σ = 24.4 mag). For the case of (ii), our lower limit to the cold neutral outflow rate is ∼100 M o˙ yr-1. The outflow kinetic energy and momentum are both much lower than predicted in energy-conserving wind models, suggesting that the AGN feedback in this quasar is not capable of completely suppressing its star formation.

Context. Characterizing the galaxy population in the early Universe holds the key to understanding the evolution of these objects and the role they played in cosmic reionization. However, there have been very few observations at the very highest redshifts to date. Aims. In order to shed light on the properties of galaxies in the high-redshift Universe and their interstellar media, we observe the Lyman-α emitting galaxy z7_GSD_3811 at z = 7.664 with bands 6 and 8 at the Atacama Large Millimeter/submillimeter Array (ALMA). Methods. We target the far-infrared [O iii] 88 µm and [C ii] 158 µm emission lines and dust continuum in the star-forming galaxy z7_GSD_3811 with ALMA. We combine these measurements with earlier observations in the rest-frame ultraviolet (UV) in order to characterize the object and compare the results to those of earlier studies that observed [O iii] and [C ii] emission in high-redshift galaxies. Results. The [O iii] 88 µm and [C ii] 158 µm emission lines are undetected at the position of z7_GSD_3811, with 3σ upper limits of 1.6 × 108 L and 4.0 × 107 L, respectively. We do not detect any dust continuum in band 6 nor band 8. The measured rms in the band 8 and band 6 continua are 26 and 9.9 µJy beam−1, respectively. Similar to several other high-redshift galaxies, z7_GSD_3811 exhibits low [C ii] emission for its star formation rate compared to local galaxies. Furthermore, our upper limit on the [O iii] line luminosity is lower than the previously observed [O iii] lines in high-redshift galaxies with similar UV luminosities. Our ALMA band 6 and 8 dust continuum observations imply that z7_GSD_3811 likely has a low dust content, and our non-detections of the [O iii] and [C ii] lines could indicate that z7_GSD_3811 has a low metallicity (Z. 0.1 Z).

Due to a mistake, the BPASS v2.0 binary-star model (Stanway et al. 2016) used in Figure 6(b) of the published article featured a different initial mass function (IMF) than the Geneva single-star model used for comparison. While the Geneva model used the Kroupa universal IMF (Kroupa 2001) with upper slope α = 2.3 (dN dM ∝ M-α) at 0.5 ≤ M(M⊙) ≤ 100, the BPASS model used a slope of α = 2.0 throughout the same mass interval. Hence, in its original form, that figure actually illustrated the combined effect of assuming binary stars and adopting a more extreme IMF. This resulted in a greater number of massive stars and a boosted ionizing flux for the BPASS model. In the revised Figure 6(b), we show the corrected comparison with identical IMF slopes (α = 2.3). In this case, the shift between the two sets of simulated galaxies in the EW(Hβ)-β diagram is more modest than in the published article. The galaxies simulated using the BPASS binary-star model are shifted by an average Δ(EW(Hβ)) ≈ 0.2 compared to galaxies simulated using the Geneva single-star model. The difference in UV slope β between the two sets of simulated galaxies is also smaller in the corrected version (Δ(β) < 0.1 on average). The risk of misclassifying high-fesc objects due using a stellar evolutionary model not representative of z > 7 galaxies is therefore somewhat smaller than indicated in the published article. (Figure Presented).

The C III] 1909 (hereafter C III]) line is the strongest ultraviolet emission line after Lyα and is therefore of interest to high-redshift studies of star-forming (SF) galaxies near the epoch of reionization. It is thought that C III] emission is strongest in galaxies with subsolar metallicity and low mass; however, spectral observations of numerous such galaxies at high and low redshift produce inconclusive or even contradictory results. We present the first-ever C III] imaging, obtained with HST/STIS for the low-redshift SF galaxy Haro 11. Cluster parameters like stellar mass, dust fraction and attenuation, and ionization parameter, obtained through spectral energy distribution fitting, show no correlation with the C III] equivalent width (EW), which may be due to a combination of the limitation of the models and the age homogeneity of the cluster population. Comparing the ratio of C III] emission line flux from individual clusters to that of Hα, [O III], and [O II], we find that the clusters with the highest EW(C III]) can be reconciled only with Cloudy models with an extremely high C/O ratio of 1.4(C/O)e for an ionizing population of single stars, binary stars, or a mixture of binary stars and active galactic nuclei. Given the pointlike nature of strong C III], the integrated total strength of EW(C III]) becomes dependent on the morphology of the galaxy, which would explain the large scatter in EW(C III]) strengths observed in galaxies with otherwise similar SF properties and of similarly low metallicity and stellar mass.

Using a sample of galaxies at z approximate to 3 with detected Lyman Continuum (LyC) leakage in the SSA22 field, we attempt to verify a proposed indirect method for identifying cases with high LyC escape fraction f(esc) based on measurements of the H beta equivalent width (EW) and the beta slope of the UV continuum. To this end, we present Keck/MOSFIRE H beta emission line flux measurements of LyC galaxies (LCGs) at spectroscopic redshifts z(spec) similar to 3.3, Lyman break galaxies (LBGs) at photometric redshifts z(phot) = 2.7-3.7, and Ly alpha emitters at z(phot) = 3.1. We also reconfirm the spectroscopic redshifts and measure the H beta emission-line fluxes from two LCGs and six LBGs. For the LCG in our sample with the most extreme f(esc), as revealed by the direct detection of LyC photons, we find that the EW(H beta)-beta method gives a broadly consistent estimate for f(esc), although the error bars remain very large. We also discuss how a combination of f(esc) measurements based on direct and indirect methods can shed light on the LyC escape mechanism and the anisotropy of the leakage.

We have conducted a comprehensive survey of emission-line galaxies at z 1.6 based on narrow-band (NB) imaging data taken with Hyper Suprime-Cam (HSC) on the Subaru telescope. In this paper, we update the catalogs of Hα, [OIII], and [OII] emission-line galaxies using the data from the second Public Data Release (PDR2) of the Subaru Strategic Program (SSP) of the HSC and Cosmic HydrOgen Reionization Unveiled with Subaru (CHORUS) survey along with the spectroscopic redshifts for 2019 emission-line galaxies selected with the PDR1 data. The wider effective coverage of NB816 and NB921, 16.3 deg2 and 16.9 deg2, respectively, are available in the Deep and UltraDeep layers of HSC-SSP from the PDR2. The CHORUS survey provides us with data with additional three NBs (NB527, NB718, and NB973) in the COSMOS field in the UltraDeep layer (1.37 deg2). The five NB datasets allow us to investigate the star-forming galaxies presenting emissionlines at 14 specific redshifts ranging from z ∼ 1.6 down to z ∼ 0.05. We revisit the distribution of large-scale structures and luminosity functions (LFs) for the emission-line galaxies with the large samples of 75377 emission-line galaxies selected. The redshift revolution of LFs shows that the star formation rate densities (SFRDs) decreases monotonically from z ∼ 1.6, which is consistent with the cosmic SFRD known to-date. Our samples of emission-line galaxies covering a sufficiently large survey volume are useful to investigate the evolution of star-forming galaxies since the cosmic noon in a wide range of environments including galaxy clusters, filaments, and voids.

We present our analysis of the Lyman continuum (LyC) emission and escape fraction of 111 spectroscopically verified galaxies with and without active galactic nuclei (AGN) from 2.26 < z < 4.3. We extended our ERS sample from Smith et al. with 64 galaxies in the GOODS North and South fields using WFC3/UVIS F225W, F275W, and F336W mosaics we independently drizzled using the HDUV, CANDELS, and UVUDF data. Among the 17 AGN from the 111 galaxies, one provided a LyC detection in F275W at m(AB) = 23.19 mag (signal-to-noise ratio, S/N, similar or equal to 133) and GALEX NUV at mAB = 23.77 mag (S/N similar or equal to 13). We simultaneously fit SDSS and Chandra spectra of this AGN to an accretion disk and Comptonization model, and find f(esc) values of f(esc)(F275W) similar or equal to 28(-4)(+20)% and f(esc)(NUV) similar or equal to 30(-5)(+22)%. For the remaining 110 galaxies, we stack image cutouts that capture their 3 LyC emission using the F225W, F275W, and F336W data of the GOODS and ERS samples, and both combined, as well as subsamples of galaxies with and without AGN, and all galaxies. We find the stack of 17 AGN dominate the LyC production from < z > similar or equal to 2.3-4.3 by a factor of similar to 10 compared to all 94 galaxies without AGN. While the IGM of the early universe may have been reionized mostly by massive stars, there is evidence that a significant portion of the ionizing energy came from AGN.

We present our new Atacama Large Millimeter/Submillimeter Array (ALMA) observations targeting [O III]88 μm, [C II]158 μm, [N II]122 μm, and dust-continuum emission for three Lyman break galaxies at z = 6.0293-6.2037, identified in the Subaru/Hyper Suprime-Cam survey. We clearly detect [O III] and [C II] lines from all of the galaxies at 4.3-11.8σ levels, and identify multi-band dust-continuum emission in two of the three galaxies, allowing us to estimate infrared luminosities and dust temperatures simultaneously. In conjunction with previous ALMA observations for six galaxies at z &gt; 6, we confirm that all the nine z = 6-9 galaxies have high [O III]/[C II] ratios of ${L}_{[{\rm{O } }{\rm{III } }]}/{L}_{[{\rm{C } }{\rm{II } }]}\sim 3\mbox{--}20$, ∼10 times higher than z ∼ 0 galaxies. We also find a positive correlation between the [O III]/[C II] ratio and the Lyα equivalent width (EW) at the ∼90% significance level. We carefully investigate physical origins of the high [O III]/[C II] ratios at z = 6-9 using Cloudy, and find that high density of the interstellar medium, low C/O abundance ratio, and the cosmic microwave background attenuation are responsible to only a part of the z = 6-9 galaxies. Instead, the observed high [O III]/[C II] ratios are explained by 10-100 times higher ionization parameters or low photodissociation region (PDR) covering fractions of 0%-10%, both of which are consistent with our [N II] observations. The latter scenario can be reproduced with a density-bounded nebula with PDR deficit, which would enhance the Lyα, Lyman continuum, and ${ { \rm{C } } }^{+}$ ionizing photons escape from galaxies, consistent with the [O III]/[C II]-Lyα EW correlation we find....

Identifying non-contaminated sample of high-redshift galaxies with escaping Lyman continuum (LyC) flux is important for understanding the sources and evolution of cosmic reionization. We present CLAUDS (CFHT Large Area u-band deep survey) u-band photometry of the COSMOS field to probe LyC radiation from spectroscopically confirmed galaxies at z ≥ 3.5 and outside the standard Lyman-break galaxy colour-selection expectations. Complementary to the CLAUDS data, we use Subaru multifilter photometry, Hubble Space Telescope (HST) multifilter imaging, and the spectroscopic surveys D10K, VUDS, and 3D-HST. We present a sample of Lyman continuum galaxy (LCG) candidates in the redshift range 3.5 ≥ z ≥ 5.1. Here, we introduce 5 LCG candidates, where two are flagged quality 1 and three quality 2. The estimated fabsesc for quality 1 candidates are in the range 5 - 73 per cent and 30 - 93 per cent . These estimates are based on our derived parameters from individual galaxies as inputs to a range of BPASS models as well as mean intergalactic medium (IGM) and maximal intergalactic and circumgalactic media (IGM+CGM) transmission. We conclude that our search for LCGs is most likely biased to lines of sight with low H i densities or free from Lyman limit systems. Our two best LCG candidates have EW (Lyα) ≤ 50 Å and we find no correlation or anticorrelation between EW (Lyα), fabsesc, and Robs, the ratio of ionizing to non-ionizing observed flux in the measured passbands. Stacking candidates without solid LyC detections (S/N < 3) results in an estimated fabsesc from galaxies not greater than 1 per cent.

Context. The first generation of stars were born a few hundred million years after the big bang. These stars synthesise elements heavier than H and He, which are later expelled into the interstellar medium, initiating the rise of metals. Within this enriched medium, the first dust grains were formed. This event is cosmologically crucial for molecule formation, as dust plays a major role by cooling low-metallicity star-forming clouds, which can fragment to create lower mass stars. Collecting information on these first dust grains is difficult because of the negative alliance of large distances and low dust masses. Aims. We aim to combine the observational information from galaxies at redshifts 5 z 10 to constrain their dust emission and theoretically understand the first evolutionary phases of the dust cycle. Methods. Spectral energy distributions (SEDs) are fitted with CIGALE and the physical parameters and their evolution are modelled. From this SED fitting, we built a dust-emission template for this population of galaxies in the reionisation epoch. Results. Our new models explain why some early galaxies are observed and others are not. We follow in time the formation of the first grains by supernovae later destroyed by other supernova blasts and expelled in the circumgalactic and intergalactic media. Conclusions. We find evidence for the first dust grains formed in the universe. But above all, this work underlines the need to collect more data and to develop new facilities to further constrain the dust cycle in galaxies in the reionisation epoch.

We report on the detection of the [C II] 157.7 μm emission from the Lyman break galaxy (LBG) MACS0416_Y1 at z = 8.3113, by using the Atacama Large Millimeter/submillimeter Array (ALMA). The luminosity ratio of [O III] 88 μm (from previous campaigns) to [C II] is 9.3 ± 2.6, indicative of hard interstellar radiation fields and/or a low covering fraction of photodissociation regions. The emission of [C II] is cospatial to the 850 μm dust emission (90 μm rest frame, from previous campaigns), however the peak [C II] emission does not agree with the peak [O III] emission, suggesting that the lines originate from different conditions in the interstellar medium. We fail to detect continuum emission at 1.5 mm (160 μm rest frame) down to 18 μJy (3σ). This non-detection places a strong limits on the dust spectrum, considering the 137 ± 26 μJy continuum emission at 850 μm. This suggests an unusually warm dust component (T &gt; 80 K, 90 per cent confidence limit), and/or a steep dust-emissivity index (β_dust &gt; 2), compared to galaxy-wide dust emission found at lower redshifts (typically T ∼ 30-50 K, β_dust ∼ 1-2). If such temperatures are common, this would reduce the required dust mass and relax the dust production problem at the highest redshifts. We therefore warn against the use of only single-wavelength information to derive physical properties, recommend a more thorough examination of dust temperatures in the early Universe, and stress the need for instrumentation that probes the peak of warm dust in the Epoch of Reionization....

Detecting HI 21-cm line in the intergalactic medium during the epoch of reionization suffers from foreground contamination such as Galactic synchrotron and extragalactic radio sources. Cross-correlation between the 21-cm line and Lyman-α emitter (LAE) galaxies is a powerful tool to identify the 21-cm signal since the 21-cm line emission has correlationwith LAEs,while the LAEs are statistically independent of the foregrounds. So far, the detectability of 21-cm- LAE cross-power spectrum has been investigated with simple LAEmodels where the observed Lyα luminosity is proportional to the dark matter halo mass. However, the previous models were inconsistent with the latest observational data of LAEs obtained with Subaru/Hyper Suprime-Cam (HSC). Here, we revisit the detectability of 21-cm-LAE cross-power spectrum adopting a state-of-the-art LAE model consistent with all Subaru/HSC observations such as the Lyα luminosity function, LAE angular autocorrelation, and the LAE fractions in the continuum selected galaxies. We find that resultant cross-power spectrum with the updated LAE model is reduced at small scales (k ∼ 1 Mpc-1) compared to the simple models, while the amplitudes at large scales (k ≲ 0.2 Mpc-1) are not affected so much. We conclude that the large-scale signal would be detectable with Square Kilometre Array (SKA) and HSC LAE cross-correlation but detecting the small-scale signal would require an extended HSC LAE survey with an area of ∼ 75 deg2or 3000 h observation time of 21-cm line with SKA.

We report on the detection of the [CII] 157.7 $\mu$m emission from the Lyman break galaxy (LBG) MACS0416_Y1 at z = 8.3113, by using the Atacama Large Millimeter/submillimeter Array (ALMA). The luminosity ratio of [OIII] 88 $\mu$m (from previous campaigns) to [CII] is 9.31 $\pm$ 2.6, indicative of hard interstellar radiation fields and/or a low covering fraction of photo-dissociation regions. The emission of [CII] is cospatial to the 850 $\mu$m dust emission (90 $\mu$m rest-frame, from previous campaigns), however the peak [CII] emission does not agree with the peak [OIII] emission, suggesting that the lines originate from different conditions in the interstellar medium. We fail to detect continuum emission at 1.5 mm (160 $\mu$m rest-frame) down to 18 $\mu$Jy (3$\sigma$). This nondetection places a strong limit on the dust spectrum, considering the 137 $\pm$ 26 $\mu$Jy continuum emission at 850 $\mu$m. This suggests an unusually warm dust component (T $&gt;$ 80 K, 90% confidence limit), and/or a steep dust-emissivity index ($\beta_{\rm dust}$ $&gt;$ 2), compared to galaxy-wide dust emission found at lower redshifts (typically T $\sim$ 30 - 50 K, $\beta_{\rm dust}$ $\sim$ 1 - 2). If such temperatures are common, this would reduce the required dust mass and relax the dust production problem at the highest redshifts. We therefore warn against the use of only single-wavelength information to derive physical properties, recommend a more thorough examination of dust temperatures in the early Universe, and stress the need for instrumentation that probes the peak of warm dust in the Epoch of Reionization....

We report on detections with the Atacama Large Millimeter/sub-millimeter Array of the far-infrared [O III] 88 μm line and the underlying dust continuum in two quasars in the reionization epoch, J205406.48-000514.8 (hereafter J2054-0005) at z = 6.0391 ± 0.0002 and J231038.88+185519.7 (hereafter J2310+1855) at z = 6.0035 ± 0.0007. The [O III] luminosities of J2054-0005 and J2310+1855 are L_{[O III]} = (6.8 ± 0.6) × 10⁹ and (2.4 ± 0.6) × 10⁹ L_☉, corresponding to ̃0.05% and 0.01% of the total infrared luminosity, L_TIR, respectively. Combining these [O III] luminosities with [C II] 158 μm luminosities in the literature, we find that J2054-0005 and J2310+1855 have [O III]-to-[C II] luminosity ratios of 2.1 ± 0.4 and 0.3 ± 0.1, respectively, the latter of which is the lowest among objects so far reported at z &gt; 6. Combining [O III] observations at z ≈ 6-9 from our study and the literature, we identify the [O III] line deficit: objects with a larger L_TIR (total infrared luminosity) have lower L_{[O III]}-to-L_TIR ratios. Furthermore, we also find that the anti-correlation is shifted toward a higher L_TIR value when compared with the local [O III] line deficit....

<title>Abstract</title>We have developed a new SED fitting tool specialized for frontier redshift galaxies. It is a common case for high-<italic>z</italic> galaxies that the available data are restricted to rich optical to near-infrared photometry and few far-infrared (FIR) data deep enough to detect the faint object (e.g., <italic>HST</italic>/WFC3 + <italic>Spitzer</italic>/IRAC + ALMA). In such situation, one cannot perform a complicated modeling of dust emission in FIR regime. We then adopt simple treatment for the dust emission using empirical LIRG templates. Instead, we adopt a sophisticated and physically motivated modeling for stellar and nebular emission parts in rest-frame UV-to-optical regime. Our new code fits not only broad band photometry but also spectral emission line flux. There is an option to fit observed SED with two templates with different physical properties. Our new code, PANHIT, is now in public, and was already applied to some high-<italic>z</italic> frontier galaxies.

<title>Abstract</title>We present a 4.7σ detection of the [OIII] 88 <italic>μ</italic>m line in a gravitationally-lensed Lyman break galaxy, RXC J2248-ID3, using the Atacama Large Millimeter/submillimeter Array (ALMA). We did not detect [CII] 158 <italic>μ</italic>m and rest-frame 90 <italic>μ</italic>m dust continuum emission, suggesting that the bulk of the interstellar medium (ISM) is ionized. Our two-component SED model combining the previous Hubble Space Telescope (HST) data and new photometry obtained from Very Large Telescope (VLT), Spitzer and ALMA suggests the presence of young (∼2 Myr) and mature (∼600 Myr) stellar components with the metallicity of <italic>Z</italic> = 0.2Z_⊙. Our findings are in contrast with previous results claiming a very young, metal-poor stellar component.

<title>Abstract</title>Recently huge amount of dust <italic>M</italic>_dust ≃ 10⁶⁻⁷<italic>M</italic>_⊙ in galaxies at <italic>z</italic> = 7–8 has been discovered by ALMA observations. The suggested timescale of the dust production was a few–several×10⁸ yr, while the stellar mass was several × 10⁹<italic>M</italic>_⊙. This amount of dust cannot be easily explained only by a supply from supernovae if we consider the dust destruction by reverse shocks. We propose that these values can be consistently explained if we take into account the grain growth in the interstellar medium (ISM). This scenario successfully reproduces the evolution of the dust mass, as well as the SFR, and stellar mass simultaneously. We conclude that even at such an early epoch of the Universe, the dust grain growth in the ISM plays a significant role in galaxies.

We present an IGM HI tomography map in a survey volume of $16 \times 19<br />
\times 131 \ h^{-3} {\rm comoving \ Mpc}^{3}$ (cMpc$^3$) centered at MAMMOTH-1<br />
nebula and three neighbouring quasars at $z=2.3$. MAMMOTH-1 nebula is an<br />
enormous Ly$\alpha$ nebula (ELAN), hosted by a type-II quasar dubbed<br />
MAMMOTH1-QSO, that extends over $1\ h^{-1}$ cMpc with not fully clear physical<br />
origin. Here we investigate the HI-gas distribution around MAMMOTH1-QSO with<br />
the ELAN and three neighbouring type-I quasars, making the IGM HI tomography<br />
map with a spatial resolution of $2.6\ h^{-1}$ cMpc. Our HI tomography map is<br />
reconstructed with HI Ly$\alpha$ forest absorption of bright background objects<br />
at $z=2.4-2.9$: one eBOSS quasar and 16 Keck/LRIS galaxy spectra. We estimate<br />
the radial profile of HI flux overdensity for MAMMOTH1-QSO, and find that<br />
MAMMOTH1-QSO resides in a volume with significantly weak HI absorption. This<br />
suggests that MAMMOTH1-QSO has a proximity zone where quasar illuminates and<br />
photo-ionizes the surrounding HI gas and suppresses HI absorption, and that the<br />
ELAN is probably a photo-ionized cloud embedded in the cosmic web. The HI<br />
radial profile of MAMMOTH1-QSO is very similar to those of three neighbouring<br />
type-I quasars at $z=2.3$, which is compatible with the AGN unification model.<br />
We compare the distributions of the HI absorption and star-forming galaxies in<br />
our survey volume, and identify a spatial offset between density peaks of<br />
star-forming galaxies and HI gas. This segregation may suggest anisotropic UV<br />
background radiation created by star-forming galaxy density fluctuations.

We report results of a search for galaxies at z > 3 with Lyman continuum (LyC) emission using a narrow-band filter NB359 with Subaru/Suprime-Cam in an similar to 800 arcmin(2) blank field around the GOODS-N. We use 103 star-forming galaxies (SFGs) and 8 active galactic nuclei (AGNs) with spectroscopic redshifts in a range between 3.06 and 3.5 and 157 photometrically selected z = 3.1 Lyman a emitter (LAE) candidates as the targets. After removing galaxies spectroscopically confirmed to be contaminated by foreground sources, we found two SFGs and one AGN as candidate LyC-emitting sources among the targets with spectroscopic redshifts. Among LAE candidates, five sources are detected in the NB359 image, and three among them may be contaminated by foreground sources. We compare the sample galaxies in the GOODS-N with those in the SSA22, where a prominent protocluster at z = 3.1 is known and an LyC search using the same NB359 filter has been made. The frequency of galaxies with LyC leakage in the SSA22 field may be about two times higher than that of galaxies in the GOODS-N with the sample ultraviolet (UV) magnitude range, although the numbers of LyC detections in these fields are too small to make a statistically significant conclusion. By combining the sample galaxies in these fields, we place the 3 sigma upper limits of the observed LyC-to-UV flux density ratio and LyC escape fraction for galaxies at z = 3.1 with absolute UV magnitude M-UV < -18.8 as (f(LyC)/f(UV))(obs) < 0.036 and f(esc)(abs) < 8 per cent, respectively.

We present our new ALMA observations targeting [OIII]88um, [CII]158um, [NII]122um, and dust continuum emission for three Lyman break galaxies at z=6.0293-6.2037 identified in the Subaru/Hyper Suprime-Cam survey. We clearly detect [OIII] and [CII] lines from all of the galaxies at 4.3-11.8sigma levels, and identify multi-band dust continuum emission in two of the three galaxies, allowing us to estimate infrared luminosities and dust temperatures simultaneously. In conjunction with previous ALMA observations for six galaxies at z&gt;6, we confirm that all the nine z=6-9 galaxies have high [OIII]/[CII] ratios of L[OIII]/L[CII]~3-20, ~10 times higher than z~0 galaxies. We also find a positive correlation between the [OIII]/[CII] ratio and the Lya equivalent width (EW) at the &gt;91% confidence level. We carefully investigate physical origins of the high [OIII]/[CII] ratios at z=6-9 using Cloudy, and find that high density of the interstellar medium, low C/O abundance ratio, and the cosmic microwave background attenuation are responsible to only a part of the z=6-9 galaxies. Instead, the observed high [OIII]/[CII] ratios are explained by 10-100 times higher ionization parameters or low photodissociation region (PDR) covering fractions of 0-10%, both of which are consistent with our [NII] observations. The latter scenario can be reproduced with a density bounded nebula with PDR deficit, which would enhance the Lya, Lyman continuum, and C+ ionizing photons escape from galaxies, consistent with the [OIII]/[CII]-Lya EW correlation we find. <P />...

We report Atacama Large Millimetre/submillimeter Array (ALMA) Cycle-5
follow-up observations of two candidate [CII] emitters at z ~ 6 in the ALMA
deep field in SSA22 (ADF22). The candidates were detected blindly in a Cycle-2
ALMA survey covering ~ 5 square arcmins, with a single tuning, along with two
CO lines associated with galaxies at lower redshifts. Various tests suggested
at least one of the two > 6-sigma [CII] candidates should be robust (Hayatsu et
al. 2017). Nevertheless, our new, deeper observations recover neither
candidate, demonstrating a higher contamination rate than expected. The cause
of the spurious detections is under investigation but at present it remains
unclarified.

The scatter in the relationship between the strength of [C II] 158 μm emission and the star formation rate at high redshift has been the source of much recent interest. Although the relationship is well established locally, several intensely star-forming galaxies have been found whose [C II] 158 μm emission is either weak, absent, or spatially offset from the young stars. Here we present new ALMA data for the two most distant gravitationally lensed and spectroscopically confirmed galaxies, A2744_YD4 at z = 8.38 and MACS1149_JD1 at z = 9.11, both of which reveal intense [O III] 88 μm emission. In both cases we provide stringent upper limits on the presence of [C II] 158 μm with respect to [O III] 88 μm. We review possible explanations for this apparent redshift-dependent [C II] deficit in the context of our recent hydrodynamical simulations. Our results highlight the importance of using several emission line diagnostics with ALMA to investigate the nature of the interstellar medium in early galaxies....

We present results from the LymAn Continuum Escape Survey (LACES), a Hubble Space Telescope (HST) program designed to characterize the ionizing radiation emerging from a sample of Lyα-emitting galaxies at redshift z ≃ 3.1. As many show intense [O III] emission characteristic of z &gt; 6.5 star-forming galaxies, they may represent valuable low-redshift analogs of galaxies in the reionization era. Using HST Wide Field Camera 3/UVIS F336W to image Lyman continuum emission, we investigate the escape fraction of ionizing photons in this sample. For 61 sources, of which 77% are spectroscopically confirmed and 53 have measures of [O III] emission, we detect Lyman continuum leakage in 20%, a rate significantly higher than is seen in individual continuum-selected Lyman break galaxies. We estimate that there is a 98% probability that ≤2 of our detections could be affected by foreground contamination. Fitting multiband spectral energy distributions (SEDs) to take account of the varying stellar populations, dust extinctions and metallicities, we derive individual Lyman continuum escape fractions corrected for foreground intergalactic absorption. We find escape fractions of 15%─60% for individual objects and infer an average 20% escape fraction by fitting composite SEDs for our detected samples. Surprisingly, however, even a deep stack of those sources with no individual F336W detections provides a stringent upper limit on the average escape fraction of less than 0.5%. We examine various correlations with source properties and discuss the implications in the context of the popular picture that cosmic reionization is driven by such compact, low-metallicity star-forming galaxies....

We present results of the cross-correlation Lya intensity mapping with<br />
Subaru/Hyper Suprime-Cam (HSC) ultra-deep narrowband images and Lya emitters<br />
(LAEs) at $z=5.7$ and $6.6$ in a total area of $4$ deg$^2$. Although<br />
overwhelming amount of data quality controls have been performed for the<br />
narrowband images and the LAE samples, we further conduct extensive analysis<br />
evaluating systematics of large-scale point spread function wings, sky<br />
subtractions, and unknown errors on the basis of physically uncorrelated<br />
signals and sources found in real HSC images and object catalogs, respectively.<br />
Removing the systematics, we carefully calculate cross-correlations between Lya<br />
intensity of the narrowband images and the LAEs. We identify very diffuse Lya<br />
emission with the $3\sigma$ ($2\sigma$) significance at $&gt;150$ comoving kpc<br />
(ckpc) far from the LAEs at $z = 5.7$ ($6.6$), beyond a virial radius of<br />
star-forming galaxies with $M_\mathrm{h} \sim 10^{11} M_\odot$. The diffuse Lya<br />
emission possibly extends up to $1,000$ ckpc with the surface brightness of<br />
$10^{-20}-10^{-19}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$. We confirm that the<br />
small-scale ($&lt;150$ ckpc) Lya radial profiles of LAEs in our Lya intensity maps<br />
are consistent with those obtained by recent MUSE observations (Leclercq et al.<br />
2017). Comparisons with numerical simulations suggest that the large-scale<br />
($\sim 150-1,000$ ckpc) Lya emission are not explained by unresolved faint<br />
sources of neighboring galaxies including satellites, but by a combination of<br />
Lya photons emitted from the central LAE and other unknown sources, such as a<br />
cold-gas stream and galactic outflow. We find no evolution in the Lya radial<br />
profiles of our LAEs from $z=5.7$ to $6.6$, where theoretical models predict a<br />
flattening of the profile slope made by cosmic reionization, albeit with our<br />
moderately large observational errors.

Recent ALMA detection of the bright [OIII] 88 um line at z = 9.11, indicates the onset of star formation at z 15. In order to uncover a large number of z=10-15 galaxies, we argue two possible pathways: (1) a blind spectroscopic survey of [OIII] 88 um line emitters, and (2) a high-cadence survey of transient sources to catch the pop-III GRBs. <P />...

Recent observations with the Atacama Large Millimeter/submillimeter Array (ALMA) detected far-infrared emission lines such as the [O III] 88 μ m line from galaxies at z ̃ 7-9. We use a cosmological simulation of galaxy formation to study the physical properties of [O III] 88 μ m emitters. In a comoving volume of 50 h^-1 Mpc on a side, we locate 34 galaxies with stellar masses greater than 10^8 M_{☉} at z = 9, and more than 270 such galaxies at z = 7. We calculate the [O III] 88 μ m luminosities (L_{O III}, 88) by combining a physical model of H II regions with emission line calculations using the photoionization code CLOUDY. We show that the resulting L_{O III}, 88, for a given star formation rate, is slightly higher than predicted from the empirical relation for local galaxies, and is consistent with recent observations of galaxies at redshifts 7-9. Bright [O III] emitters with L_{O III}, 88 &gt; 10^8 L_{☉} have star formation rates higher than 3 M_{☉} yr^{-1}, and the typical metallicity is {̃ } 0.1 Z_{☉}. The galaxies are hosted by dark matter haloes with masses greater than 10^{11} M_{☉}. We propose to use the [O III] 5007 Å line, to be detected by James Webb Space Telescope, to study the properties of galaxies whose [O III] 88 μ m line emission has been already detected with ALMA....

With the Atacama Large Millimeter/sub-millimeter Array (ALMA), we report detections of the far-infrared (FIR) [OIII] 88 $\mu$m line and the underlying dust continuum in the two quasars in the reionization epoch, J205406.48-000514.8 (hereafter J2054-0005) at $z=6.0391\pm0.0002$ and J231038.88+185519.7 (hereafter J2310+1855) at $z=6.0035\pm0.0007$. The [OIII] luminosity of J2054-0005 and J2310+1855 are $L_{\rm [OIII]} = (6.8\pm0.6) \times 10^{9}$ and $(2.4\pm0.6) \times 10^{9}$ $L_{\rm \odot}$, corresponding to $\approx$ 0.05\%\ and 0.01\%\ of the total infrared luminosity, $L_{\rm TIR}$, respectively. Combining these [OIII] luminosities with [CII] 158 $\mu$m luminosities in the literature, we find that J2054-0005 and J2310+1855 have the [OIII]-to-[CII] luminosity ratio of $2.1\pm0.4$ and $0.3\pm0.1$, respectively, the latter of which is the lowest among objects so far reported at $z&gt;6$. Combining [OIII] observations at $z\approx6-9$ from our study and the literature, we identify the [OIII] line deficit: objects with larger $L_{\rm TIR}$ have lower $L_{\rm [OIII]}$-to-$L_{\rm TIR}$ ratios. Furthermore, we also find that the anti-correlation is shifted toward higher $L_{\rm TIR}$ value when compared to the local [OIII] line deficit. <P />...

Hyper Suprime-Cam (HSC) is a wide-field imaging camera on the prime focus of the 8.2-m Subaru telescope on the summit of Mauna Kea in Hawaii. A team of scientists from Japan, Taiwan, and Princeton University is using HSC to carry out a 300-night multi-band imaging survey of the high-latitude sky. The survey includes three layers: the Wide layer will cover 1400 deg2 in five broad bands (grizy), with a 5 σ point-source depth of r ≈ 26. The Deep layer covers a total of 26 deg2 in four fields, going roughly a magnitude fainter, while the UltraDeep layer goes almost a magnitude fainter still in two pointings of HSC (a total of 3.5 deg2). Here we describe the instrument, the science goals of the survey, and the survey strategy and data processing. This paper serves as an introduction to a special issue of the Publications of the Astronomical Society of Japan, which includes a large number of technical and scientific papers describing results from the early phases of this survey.

We investigate the X-ray active galactic nucleus (AGN) properties of millimeter galaxies in the Great Observatories Origins Deep Survey South (GOODS-S) field detected with the Atacama Large Millimeter/submillimeter Array (ALMA), by utilizing the Chandra 7-Ms data, the deepest X-ray survey to date. Our millimeter galaxy sample comes from the ASAGAO survey covering 26 arcmin² (12 sources at a 1.2 mm flux-density limit of ≈ 0.6 mJy), supplemented by the deeper but narrower 1.3 mm survey of a part of the ASAGAO field by Dunlop et al. Ofthe 25 total millimeter galaxies, 14 have Chandra counterparts. The observed AGN fractions at z=1.5{--}3 are found to be {90}_-19⁺⁸% and {57}_-25⁺²³% for the ultra-luminous and luminous infrared galaxies with log {L}_{IR}/{L}_☉ = 12-12.8 and log {L}_{IR}/{L}_☉ = 11.5-12, respectively. The majority (̃2/3) of the ALMA and/or Herschel detected X-ray AGNs at z = 1.5-3 appear to be star-formation-dominant populations, having {L}_{{ { X} } }/ {L}_{IR} ratios smaller than the “simultaneous evolution” value expected from the local black-hole-mass-to-stellar-mass ({M}_{BH}-M _*) relation. On the basis of the {L}_{{ { X} } } and stellar mass relation, we infer that a large fraction of star-forming galaxies at z=1.5{--}3 have black hole masses that are smaller than those expected from the local {M}_{BH}-M _* relation. This contrasts previous reports on luminous AGNs at the same redshifts detected in wider and shallower surveys, which are subject to selection biases against lower luminosity AGNs. Our results are consistent with an evolutionary scenario in which star formation occurs first, and an AGN-dominant phase follows later, in objects that finally evolve into galaxies with classical bulges....

We investigate the impact of radiation pressure on spatial dust distribution inside HII regions using one-dimensional radiation hydrodynamic simulations, which include absorption and reemission of photons by dust. In order to investigate grain-size effects as well, we introduce two additional fluid components describing large and small dust grains in the simulations. Relative velocity between dust and gas strongly depends on the drag force. We include collisional drag force and coulomb drag force. We find that, in a compact HII region, a dust cavity region is formed by radiation pressure. Resulting dust cavity sizes (~0.2 pc) agree with observational estimates reasonably well. Since dust inside an HII region is strongly charged, relative velocity between dust and gas is mainly determined by the coulomb drag force. Strength of the coulomb drag force is about 2 order of magnitude larger than that of the collisional drag force. In addition, in a cloud of mass 105 M⊙, we find that the radiation pressure changes the grain-size distribution insideHII regions. Since large (0.1 μm) dust grains are accelerated more efficiently than small (0.01 μm) grains, the large-to-small grain mass ratio becomes smaller by an order of magnitude compared with the initial one. Resulting dust-size distributions depend on the luminosity of the radiation source. The large and small grain segregation becomes weaker when we assume stronger radiation source, since dust grain charges become larger under stronger radiation and hence coulomb drag force becomes stronger.

We report the identification of four millimeter line-emitting galaxies with the Atacama Large Milli/submillimeter Array (ALMA) in SSA22 Field (ADF22). We analyze the ALMA 1.1-mm survey data, with an effective survey area of 5 arcmin², frequency ranges of 253.1-256.8 and 269.1-272.8 GHz, angular resolution of 0{^''_.}7 and rms noise of 0.8 mJy beam^-1 at 36 km s^-1 velocity resolution. We detect four line-emitter candidates with significance levels above 6σ. We identify one of the four sources as a CO(9-8) emitter at z = 3.1 in a member of the proto-cluster known in this field. Another line emitter with an optical counterpart is likely a CO(4-3) emitter at z = 0.7. The other two sources without any millimeter continuum or optical/near-infrared counterpart are likely to be [C II] emitter candidates at z = 6.0 and 6.5. The equivalent widths of the [C II] candidates are consistent with those of confirmed high-redshift [C II] emitters and candidates, and are a factor of 10 times larger than that of the CO(9-8) emitter detected in this search. The [C II] luminosity of the candidates are 4-7 × 10⁸ L_☉. The star formation rates (SFRs) of these sources are estimated to be 10-20 M_☉ yr^-1 if we adopt an empirical [C II] luminosity-SFR relation. One of them has a relatively low S/N ratio, but shows features characteristic of emission lines. Assuming that at least one of the two candidates is a [C II] emitter, we derive a lower limit of [C II]-based star formation rate density (SFRD) at z ̃ 6. The resulting value of &gt;10^-2 M_☉ yr^-1 Mpc^-3 is consistent with the dust-uncorrected UV-based SFRD. Future millimeter/submillimeter surveys can be used to detect a number of high-redshift line emitters, with which to study the star formation history in the early universe....

Using galaxies as background light sources to map intervening Ly a absorption is a novel approach to study the interplay among galaxies, the circumgalactic medium (CGM) and the intergalactic medium. Introducing a new measure of z = 3.1 HI Ly alpha absorption relative to the cosmic mean, Delta NB497, estimated from photometric data of star-forming galaxies at 3.3 less than or similar to z less than or similar to 3.5, we have made two-dimensional Delta NB497 maps in the z = 3.1 SSA22 protocluster region and two control fields (Subaru/XMM-Newton Deep Survey; Great Observatory Optical Deep Survey North) with a spatial resolution of similar to 5 comoving Mpc. The Delta NB497 measurements in the SSA22 field are systematically larger than those in the control fields, and this HI absorption enhancement extends more than 50 comovingMpc. The field-averaged (i. e. similar to 50 comovingMpc scale) Delta NB497 and the overdensity of Ly alpha emitters (LAEs) seem to be correlated, while there is no clear dependency of the Delta NB497 on the local LAE overdensity in a few comoving Mpc scale. These results suggest that diffuse HI gas spreads out in/around the SSA22 protocluster. We have also found an enhancement of Delta NB497 at a projected distance &lt; 100 physical kpc from the nearest z = 3.1 galaxies at least in the SSA22 field, which is probably due to HI gas associated with the CGM of individual galaxies. The HI absorption enhancement in the CGM-scale tends to be weaker around galaxies with stronger Ly alpha emission, which suggests that the Ly alpha escape fraction from galaxies depends on hydrogen neutrality in the CGM.

Using four different suites of cosmological simulations, we generate synthetic spectra for galaxies with different Lyman-continuum escape fractions (f(esc)) at redshifts z approximate to 7-9, in the rest-frame wavelength range relevant for the James Webb Space Telescope (JWST) NIRSpec instrument. By investigating the effects of realistic star formation histories and metallicity distributions on the EW(H beta)-beta diagram (previously proposed as a tool for identifying galaxies with very high f(esc)), we find that neither of these effects are likely to jeopardize the identification of galaxies with extreme Lyman-continuum leakage. Based on our models, we expect that essentially all z approximate to 7-9 galaxies that exhibit rest-frame EW(Hb). 30 angstrom to have f(esc) &gt; 0.5. Incorrect assumptions concerning the ionizing fluxes of stellar populations or the dust properties of z &gt; 6 galaxies can in principle bias the selection, but substantial model deficiencies of this type should at the same time be evident from offsets in the observed distribution of z &gt; 6 galaxies in the EW(H beta)-beta diagram compared to the simulated distribution. Such offsets would thereby allow JWST/NIRSpec measurements of these observables to serve as input for further model refinement.

We present the largest to date sample of hydrogen Lyman continuum (LyC) emitting galaxy candidates at any redshift, with 18 Lyman alpha emitters (LAEs) and seven Lyman break galaxies (LBGs), obtained from the SSA22 field with Subaru/Suprime-Cam. The sample is based on the 159 LAEs and 136 LBGs observed in the field, all with spectroscopically confirmed redshifts, and these LyC candidates are selected as galaxies with counterparts in a narrow-band filter image which traces LyC at z &gt;= 3.06. Many LyC candidates show a spatial offset between the rest-frame non-ionizing ultraviolet (UV) detection and the LyC-emitting substructure or between the Ly alpha emission and LyC. The possibility of foreground contamination complicates the analysis of the nature of LyC emitters, although statistically it is highly unlikely that all candidates in our sample are contaminated by foreground sources. Many viable LyC LAE candidates have flux density ratios inconsistent with standard models, while also having too blue UV slopes to be foreground contaminants. Stacking reveals no significant LyC detection, suggesting that there is a dearth of objects with marginal LyC signal strength, perhaps due to a bimodality in the LyC emission. The foreground contamination corrected 3 sigma upper limits of the observed average flux density ratios are f(LyC)/f(UV) &lt; 0.08 from stacking LAEs and f(LyC)/f(UV) &lt; 0.02 from stacking LBGs. There is a sign of a positive correlation between LyC and Ly alpha, suggesting that both types of photons escape via a similar mechanism. The LyC detection rate among protocluster LBGs is seemingly lower compared to the field.

Subaru/SuprimeCam narrow-band photometry of the SSA22 field reveals the presence of four Lyman continuum (LyC) candidates among a sample of 14 active galactic nuclei (AGNs). Two show offsets and likely have stellar LyCin nature or are foreground contaminants. The remaining two LyC candidates are type I AGN. We argue that the average LyC escape fraction of high-redshift, low-luminosityAGNis not likely to be unity, as often assumed in the literature. From direct measurement we obtain the average LyC-to-UV flux density ratio and ionizing emissivity for a number of AGN classes and find it at least a factor of 2 lower than values obtained assuming f(esc) = 1. Comparing to recent Ly alpha forest measurements, AGNs at redshift z similar to 3 make up at most similar to 12 per cent and as little as similar to 5 per cent of the total ionizing budget. Our results suggest that AGNs are unlikely to dominate the ionization budget of the Universe at high redshifts.

We have performed very large and high-resolution cosmological hydrodynamic simulations in order to investigate detectability of nebular lines in the rest-frame ultraviolet (UV) to optical wavelength range from galaxies at z &gt; 7. We find that the expected line fluxes are very well correlated with the apparent UV magnitudes. The C-IV 1549 angstrom and C III] 1909 angstrom lines of galaxies brighter than 26 AB magnitudes are detectable with current facilities such as the Very Large Telescope (VLT) XShooter and the Keck Multi-Object Spectrometer for Infra-Red Exploration (MOSFIRE). Metal lines such as C-IV 1549 angstrom, C III] 1909 angstrom, [O II] 3727 angstrom and [O III] 4959/5007 angstrom are good targets for spectroscopic observation with the Thirty-Metre Telescope (TMT), European Extremely Large Telescope (E-ELT), Giant Magellan Telescope (GMT) and James Webb Space Telescope (JWST). We also expect Ha and H beta lines to be detectable with these telescopes. Additionally, we predict the detectability of nebular lines for z &gt; 10 galaxies, which will be found with JWST, the Wide-Field Infrared Survey Telescope (WFIRST) and First Light And Reionization Explorer (FLARE) (11 &lt;= z &lt;= 15). We conclude that the C-IV 1549 angstrom, C III] 1909 angstrom, [O III] 4959/5007 angstrom and H beta lines from even z similar to 15 galaxies could be strong targets for TMT, E-ELT and JWST. We also find that magnification by gravitational lensing is of great help in detecting such high-z galaxies. According to our model, the C III] 1909 angstrom line in z &gt; 9 galaxy candidates is detectable even using current facilities.

We present a new analysis of multi-epoch, H-band, scattered light images of the AB Aur system. We use a Monte Carlo radiative transfer code to simultaneously model the system's spectral energy distribution (SED) and H-band polarized intensity (PI) imagery. We find that a disk-dominated model, as opposed to one that is envelope-dominated, can plausibly reproduce AB Aur's SED and near-IR imagery. This is consistent with previous modeling attempts presented in the literature and supports the idea that at least a subset of AB Aur's spirals originate within the disk. In light of this, we also analyzed the movement of spiral structures in multi-epoch H-band total light and PI imagery of the disk. We detect no significant rotation or change in spatial location of the spiral structures in these data, which span a 5.8-year baseline. If such structures are caused by disk-planet interactions, the lack of observed rotation constrains the location of the orbit of planetary perturbers to be >47 au.

We made near-infrared multicolor imaging observations of a disk around Herbig Be star HD. 100546 using Gemini/NICI. K (2.2 mu m), H2O ice (3.06 mu m), and L' (3.8 mu m) disk images were obtained and we found a 3.1 mu m absorption feature in the scattered light spectrum, likely due to water ice grains at the disk surface. We compared the observed depth of the ice absorption feature with the disk model based on Oka et al., including the water ice photodesorption effect by stellar UV photons. The observed absorption depth can be explained by both the disk models with and without the photodesorption effect within the measurement accuracy, but the model with photodesorption effects is slightly more favored, implying that the UV photons play an important role in the survival/destruction of ice grains at the Herbig Ae/Be disk surface. Further improvement to the accuracy of the observations of the water ice absorption depth is needed to constrain the disk models.

Cosmic reionization is known to be a major phase transition of the gas in the<br />
Universe. Since astronomical objects formed in the early Universe, such as the<br />
first stars, galaxies and black holes, are expected to have caused cosmic<br />
reionization, the formation history and properties of such objects are closely<br />
related to the reionization process. In spite of the importance of exploring<br />
reionization, our understandings regarding reionization is not sufficient yet.<br />
Square Kilometre Array (SKA) is a next-generation large telescope that will be<br />
operated in the next decade. Although several programs of next-generation<br />
telescopes are currently scheduled, the SKA will be the unique telescope with a<br />
potential to directly observe neutral hydrogen up to z~30, and provide us with<br />
valuable information on the Cosmic Dawn (CD) and the Epoch of Reionization<br />
(EoR). The early science with the SKA will start in a few years; it is thus the<br />
time for us to elaborate a strategy for CD/EoR Science with the SKA. The<br />
purpose of this document is to introduce Japanese scientific interests in the<br />
SKA project and to report results of our investigation.

銀河間の中性水素雲の中でも最高密度のものをDamped Lyman α(DLA)系と呼ぶ。従来のDLAは、見かけの光源サイズ(天球面上の面積)が無視できるほど小さい点光源の視線上で発見されてきた。この論文では、見かけのサイズが無視できない遠方銀河の視線上のDLAの発見を報告している。このDLAについて、中性水素雲のサイズに下限値を与え、この雲に付随する天体の星形成率などを制限した。

Gravitationally lensed galaxies with magnification mu approximate to 10-100 are routinely detected at high redshifts, but magnifications significantly higher than this are hampered by a combination of low probability and large source sizes. Magnifications of mu similar to 1000 may none the less be relevant in the case of intrinsically small, high-redshift objects with very high number densities. Here, we explore the prospects of detecting compact (less than or similar to 10 pc), high-redshift (z greater than or similar to 7) Population III star clusters at such extreme magnifications in large-area surveys with planned telescopes like Euclid, Wide Field Infrared Survey Telescope and Wide-field Imaging Surveyor for High-redshift (WISH). We find that the planned WISH 100 deg(2) ultradeep survey may be able to detect a small number of such objects, provided that the total stellar mass of these star clusters is greater than or similar to 10(4) M-circle dot. If candidates for such lensed Population III star clusters are found, follow-up spectroscopy of the surrounding nebula with the James Webb Space Telescope or ground-based Extremely Large Telescopes should be able to confirm the Population III nature of these objects. Multiband photometry of these objects with the James Webb Space Telescope also has the potential to confirm that the stellar initial mass function in these Population III star clusters is top-heavy, as supported by current simulations.

Aims. We aim to investigate the effect of the escaping ionizing radiation on the color selection of high-redshift galaxies and identify candidate Lyman-continuum (LyC) emitters.
Methods. We used the intergalactic medium (IGM) prescription of Inoue et al. (2014, MNRAS, 442, 1805) and galaxy synthesis models of Bruzual & Charlot (2003, MNRAS, 344, 1000) to properly treat the ultraviolet stellar emission and the stochasticity of the intergalactic transmission and mean free path in the ionizing regime. Color tracks were computed by turning the escape fraction fesc of ionizing radiation on or off.
Results. At variance with recent studies, a careful treatment of IGM transmission leads to no significant effects on the high-redshift broad-band color selection, even adopting the most extreme ionizing emission model (with an age of 1 Myr, zero dust, and metallicity Z/Z(circle dot) = 0.02). The decreasing mean free path of ionizing photons with increasing redshift further diminishes the contribution of the LyC to broad-band colors. We demonstrate that prominent LyC sources can be selected under suitable conditions by calculating the probability of a null escaping ionizing radiation. This was performed by running ad hoc Monte Carlo simulations anchored to the observed photometry, exploring the stochasticity of the IGM, and comparing the simulated and observed colors that encompass the Lyman edge. The method was applied to a sample of galaxies extracted from the GOODS-S field. A known LyC source at z = 3.795 was successfully recovered as a LyC-emitter candidate, and another convincing candidate at z = 3.212 is reported. A detailed analysis of the two sources (including their variability and morphology) suggests a possible mixture of stellar and non-stellar (AGN) contribution in the ultraviolet.
Conclusions. The classical broad-band color selection of 2.5 &lt; z &lt; 4.5 galaxies does not prevent the inclusion of LyC emitters in the selected samples. High fesc in relatively bright galaxies (L &gt; 0.1L(star)) could be favored by the presence of a faint active galactic nucleus (AGN) that is not easily detected at any wavelength. A hybrid stellar and non-stellar (AGN) ionizing emission could coexist in these systems and explain the tensions found among the UV excess and the stellar population synthesis models reported in literature.

宇宙の構造形成論において、初期宇宙の銀河数密度を調べることは重要である。この論文では、宇宙年齢15億年頃にある、水素ライマンα輝線星雲を持ち、強い電波を放射している銀河の環境を調査した。電波銀河の周囲にある水素ライマンα輝線で明るい銀河をすばる望遠鏡で探査した結果、電波銀河周囲の銀河数密度は一般的な領域に比べて有意に高かった。この電波銀河を中心にして、巨大な銀河団(メンバー数が1,000個を超えるような銀河の集団)に成長する可能性がある。

We present near-IR (NIR) and far-UV observations of the pre-transitional (gapped) disk in HD 169142 using NASA's Infrared Telescope Facility and Hubble Space Telescope. The combination of our data along with existing data sets into the broadband spectral energy distribution reveals variability of up to 45% between similar to 1.5-10 mu m over a maximum timescale of 10 yr. All observations known to us separate into two distinct states corresponding to a high near-IR state in the pre-2000 epoch and a low state in the post-2000 epoch, indicating activity within the less than or similar to 1AU region of the disk. Through analysis of the Pa beta and Br gamma lines in our data we derive a mass accretion rate in 2013 May of (M)overdot approximate to (1.5-2.7) x 10-9 M-circle dot yr(-1). We present a theoretical modeling analysis of the disk in HD 169142 using Monte-Carlo radiative transfer simulation software to explore the conditions and perhaps signs of planetary formation in our collection of 24 yr of observations. We find that shifting the outer edge (r approximate to 0.3AU) of the inner disk by 0.05 AU toward the star (in simulation of accretion and/or sculpting by forming planets) successfully reproduces the shift in NIR flux. We establish that the similar to 40-70 AU dark ring imaged in the NIR by Quanz et al. and Momose et al. and at 7 mm by Osorio et al. may be reproduced with a 30% scaled density profile throughout the region, strengthening the link to this structure being dynamically cleared by one or more planetary mass bodies.

It has been proposed that supermassive black holes (SMBHs) are originated from direct-collapse black holes (DCBHs) that are formed at z greater than or similar to 10 in the primordial gas in the case where H-2 cooling is suppressed by strong external radiation. In this work, we study the critical specific intensity J(crit) required for DCBH formation for various radiation spectral shapes by a series of one-zone calculations of a collapsing primordial-gas cloud. We calculate the critical specific intensity at the Lyman-Werner (LW) bands J(LW,21)(crit) (in units of 10(-21) erg s(-1) Hz(-1) sr(-1) cm(-2)) for realistic spectra of metal-poor galaxies. We find that J(crit) is not sensitive to the age or metallicity for the constant star formation galaxies with J(LW,21)(crit) = 1300-1400, while J(crit) decreases as galaxies become older or more metal-enriched for the instantaneous starburst galaxies. However, for the young (the age &lt; 100 Myr) and/or extremely metal poor (Z &lt; 5 x 10(-4) Z(circle dot)) instantaneous starburst galaxies, such dependence is not strong and J(LW,21)(crit) = 1000-1400. We also find that J(crit) is solely determined by the ratio between the H- and H-2 photodissociation rate coefficients, k(H-,pd)/k(H2,pd), with which we develop a formula to estimate J(crit) for a given spectrum. The higher value of J(crit) for the realistic spectra than those expected in the literature significantly reduces the estimated DCBH number density n(DCBH). By extrapolating the result of Dijkstra, Ferrara & Mesinger, we obtain n(DCBH) similar to 10(-10) cMpc(-3) at z = 10, which is roughly consistent with the observed number density of high-redshift SMBHs n(SMBH) similar to 10(-9) cMpc(-3) at z similar to 6, considering large uncertainties in the estimation.

We have performed a large cosmological hydrodynamics simulation tailored to the deep survey with the Hubble Space Telescope made in 2012, the so-called UDF12 campaign. After making a light-cone output, we have applied the same colour-selection criteria as the UDF12 campaign to select galaxies from our simulation, and then, have examined the physical properties of them as a proxy of the real observed UDF12 galaxies at z &gt; 7. As a result, we find that the halo mass is almost linearly proportional to the observed ultraviolet (UV) luminosity (4 x 10(11)M(circle dot) at M-UV = -21). The dust attenuation and UV slope beta well correlates with the observed UV luminosity, which is consistent with observations quantitatively. The star formation rate (SFR) is also linearly proportional to the stellar mass and the specific SFR shows only a weak dependence on the mass. We also find an increasing star formation history with a time-scale of similar to 100 Myr in the high-z galaxies. An average metallicity weighted by the Lyman continuum luminosity reaches up to &gt; 0.1 Solar even at z similar to 10, suggesting a rapid metal enrichment. We also expect &gt;= 0.1 mJy at 350 GHz of the dust thermal emission from the galaxies with H-160 &lt; 27, which can be detectable with the Atacama Large Millimetre-sub-millimetre Array. The galaxies selected by the UDF12 survey contribute to only 52-12 per cent of the cosmic SFR density from z similar to 7 to z similar to 10, respectively. The James Webb Space Telescope will push the detection fraction up to 77-72 per cent.

The fraction of ionizing photons that escape (f(esc)) from z greater than or similar to 6 galaxies is an important parameter for assessing the role of these objects in the reionization of the universe, but the opacity of the intergalactic medium precludes a direct measurement of f(esc) for individual galaxies at these epochs. We argue that since f(esc) regulates the impact of nebular emission on the spectra of galaxies, it should nonetheless be possible to indirectly probe f(esc) well into the reionization epoch. As a first step, we demonstrate that by combining measurements of the rest-frame UV slope beta with the equivalent width of the H beta emission line, galaxies with very high Lyman continuum escape fractions (f(esc) &gt;= 0.5) should be identifiable up to z approximate to 9 through spectroscopy with the upcoming James Webb Space Telescope (JWST). By targeting strongly lensed galaxies behind low-redshift galaxy clusters, JWST spectra of sufficiently good quality can be obtained for M-1500 less than or similar to -16.0 galaxies at z approximate to 7 and for M-1500 less than or similar to -17.5 galaxies at z approximate to 9. Dust-obscured star formation may complicate the analysis, but supporting observations with ALMA or the planned SPICA mission may provide useful constraints on this effect.

銀河の恒星質量分布関数は、近傍から遠方宇宙まで観測が進められており、銀河形成進化モデルと比較することで、モデルの標準的なテストとして用いられている。しかし、観測から導出した恒星質量と、モデルの恒星質量の定義が異なる場合が多々ある。この論文では、白色矮星など恒星の残骸の質量を含めるか否かでモデル恒星質量関数がどれほど異なるか検討し、場合によっては無視できない違いが現れることを指摘した。

遠方宇宙（約100億光年）の二つの銀河が、視線上に極めて近く並んでいるのが見つかり、その重力レンズ効果について検討した論文。天球上の離角はわずか0.6秒という小ささにも関わらず、重力レンズ効果はそれほどないことが分かった。その理由は、手前の銀河の質量が非常に小さいからである。

The galaxy spectra we observe are attenuated by dust, produced in galaxies themselves. However, in studies of galaxy evolution, a genuine galaxy spectrum without attenuation is often needed, and the evolution of the attenuation curve is also fundamental for the investigation for the evolution of dust in galaxies. We show one of the important aspects of dust attenuation, the infrared excessultraviolet spectral slope (IRX-β) relation by using the data from MUSYC and GOODS-Herschel projects. We found that the IRX-β relation does not show significant evolution from z=0 to z3, with a very large scatter.

The cosmic star formation rate density (CSFRD) has been observationally investigated out to redshift z similar or equal to 10. However, most of the theoretical models for galaxy formation underpredict the CSFRD at z greater than or similar to 1. Since the theoretical models reproduce the observed luminosity functions (LFs), luminosity densities (LDs), and stellar mass density at each redshift, this inconsistency does not simply imply that theoretical models should incorporate some missing unknown physical processes in galaxy formation. Here, we examine the cause of this inconsistency at UV wavelengths by using a mock catalog of galaxies generated by a semi-analytic model of galaxy formation. We find that this inconsistency is due to two observational uncertainties: the dust obscuration correction and the conversion from UV luminosity to star formation rate (SFR). The methods for correction of obscuration and SFR conversion used in observational studies result in the overestimation of the CSFRD by similar to 0.1-0.3 dex and similar to 0.1-0.2 dex, respectively, compared to the results obtained directly from our mock catalog. We present new empirical calibrations for dust attenuation and conversion from observed UV LFs and LDs into the CSFRD.

This paper investigates the main driver of dust mass growth in the interstellar medium (ISM) by using a chemical evolution model of a galaxy with metals (elements heavier than helium) in the dust phase, in addition to the total amount of metals. We consider asymptotic giant branch (AGB) stars, type II supernovae (SNe II), and dust mass growth in the ISM, as the sources of dust, and SN shocks as the destruction mechanism of dust. Furthermore, to describe the dust evolution precisely, our model takes into account the age and metallicity (the ratio of metal mass to ISM mass) dependence of the sources of dust. We have particularly focused on the dust mass growth, and found that in the ISM this is regulated by the metallicity. To quantify this aspect, we introduce a "critical metallicity", which is the metallicity at which the contribution of stars (AGB stars and SNe II) equals that of the dust mass growth in the ISM. If the star-formation timescale is shorter, the value of the critical metallicity is higher, but the galactic age at which the metallicity reaches the critical metallicity is shorter. From observations, it was expected that the dust mass growth was the dominant source of dust in the Milky Way and dusty QSOs at high redshifts. By introducing a critical metallicity, it is clearly shown that the dust mass growth is the main source of dust in such galaxies with various star-formation timescales and ages. The dust mass growth in the ISM is regulated by metallicity, and we emphasize that the critical metallicity serves as an indicator to judge whether the grain growth in the ISM is the dominant source of dust in a galaxy, especially because of the strong, and nonlinear, dependence on the metallicity.

The relation between the ratio of infrared (IR) and ultraviolet (UV) flux densities (the infrared excess: IRX) and the slope of the UV spectrum (beta) of galaxies plays a fundamental role in the evaluation of the dust attenuation of star-forming galaxies, especially at high redshifts. Many authors, however, have pointed out that there is a significant dispersion and/or deviation from the originally proposed IRX-beta relation depending on sample selection. We reexamined the IRX-beta relation by measuring the far-and near-UV flux densities of the original sample galaxies with GALEX and AKARI imaging data and constructed a revised formula. We found that the newly obtained IRX values were lower than the original relation because of the significant underestimation of the UV flux densities of the galaxies, caused by the small aperture of IUE. Furthermore, since the original relation was based on IRAS data that covered a wavelength range of lambda = 42-122 mu m, we obtained an appropriate IRX-beta relation with total dust emission (TIR): log(L-TIR/L-FUV) = log[10(0.4(3.06+1.58 beta)) - 1] + 0.22 using the data from AKARI, which has wider wavelength coverage toward longer wavelengths. This new relation is consistent with most of the preceding results for samples selected at optical and UV, though there is significant scatter around it. We also found that even the quiescent class of IR galaxies follows this new relation, though luminous and ultraluminous IR galaxies distribute completely differently as previously thought.

We investigate the effect of photodesorption on the snow line position at the surface of a protoplanetary disk around a Herbig Ae/Be star, motivated by the detection of water ice particles at the surface of the disk around HD142527 by Honda et al. For this aim, we obtain the density and temperature structure in the disk with a 1+1D radiative transfer and determine the distribution of water ice particles in the disk by the balance between condensation, sublimation, and photodesorption. We find that photodesorption induced by far-ultraviolet radiation from the central star depresses the ice-condensation front toward the mid-plane and pushes the surface snow line significantly outward when the stellar effective temperature exceeds a certain critical value. This critical effective temperature depends on the stellar luminosity and mass, the water abundance in the disk, and the yield of photodesorption. We present an approximate analytic formula for the critical temperature. We separate Herbig Ae/Be stars into two groups on the HR diagram according to the critical temperature: one is the disks where photodesorption is effective and from which we may not find ice particles at the surface, and the other is the disks where photodesorption is not effective. We estimate the snow line position at the surface of the disk around HD142527 to be 100-300 AU, which is consistent with the water ice detection at &gt;140 AU in the disk. All the results depend on the dust grain size in a complex way, and this point requires more work in the future.

第一世代銀河を発見することは現代天文学の重要課題である。その種の銀河の特徴として、極めて強い水素ライマンα輝線が挙げられる。これまで得られている長遠方銀河探査データの中に、この強いライマンα輝線の特徴を備えた第一世代銀河候補がすでにあることを報告した論文。今後の詳細な調査が待たれる。

We present results of a survey of Ly alpha emitters (LAEs) at z = 6.5 which is thought to be the final epoch of the cosmic re-ionization. In a approximate to 530 arcmin2 deep image of the SSA22 field taken through a narrow-band filter NB912 installed in the Subaru/Suprime-Cam, we have found only 14 LAE candidates with L-Ly alpha greater than or similar to 3 x 1042 erg s-1. Even applying the same colour selection criteria, the number density of the LAE candidates is a factor of 3 smaller than that found at the same redshift in the Subaru Deep Field (SDF). Assuming the number density in the SDF is a cosmic average, the probability to have a number density equal to or smaller than that found in the SSA22 field is only 7 per cent if we consider fluctuation by the large-scale structure (i.e. cosmic variance) and Poisson error. Therefore, the SSA22 field may be a rare void at z = 6.5. On the other hand, we have found that the number density of i'-drop galaxies with 25.5 &lt; z' &lt; 26.0 in the SSA22 field agrees well with that in the SDF. If we consider a scenario that a larger neutral fraction of intergalactic hydrogen, x(H I), in the SSA22 field obscures a part of Ly alpha emission, x(H I) in the SSA22 field should be about two times larger than that in the SDF. This can be translated into x(H I) &lt; 0.9 at z = 6.5 in the SSA22 field. A much larger survey area than previous ones is required to overcome a large fluctuation reported here and to obtain a robust constraint on x(H I) at the end of the re-ionization from LAEs.

すばる望遠鏡で発見した電離光子放射銀河を、ヨーロッパ南天天文台のVery Large Telescopeで分光観測し、その性質を詳しく調べた。まず、分光観測により、銀河の距離が正確に求まった結果、すばる望遠鏡で検出した放射は間違いなく電離光子であると確認できた。次に、観測された電離光子放射強度はこれまでの理論モデルでは説明がつかないほど強いが、もし重元素の極めて少ない大質量の恒星が存在すれば、観測強度が説明できることが分かった。したがって、この種の銀河にはそのような恒星が大量に含まれている可能性が高い。

We use ultra-deep ultraviolet VLT/VIMOS intermediate-band and VLT/FORS1 narrowband imaging in the GOODS Southern field to derive limits on the distribution of the escape fraction (f(esc)) of ionizing radiation for L &gt;= L-z=3* Lyman-break galaxies (LBGs) at redshift 3.4-4.5. Only one LBG, at redshift z = 3.795, is detected in its Lyman continuum (LyC; S/N similar or equal to 5.5), the highest redshift galaxy currently known with a direct detection. Its ultraviolet morphology is quite compact (R-eff = 0.8 kpc physical). Three out of seven active galactic nuclei are also detected in their LyC, including one at redshift z = 3.951 and z(850) = 26.1. From stacked data (LBGs), we set an upper limit to the average f(esc) in the range 5%-20%, depending on how the data are selected (e. g., by magnitude and/or redshift). We undertake extensive Monte Carlo simulations that take into account intergalactic attenuation, stellar population synthesis models, dust extinction, and photometric noise in order to explore the moments of the distribution of the escaping radiation. Various distributions (exponential, log-normal, and Gaussian) are explored. We find that the median f(esc) is lower than similar or equal to 6% with an 84% percentile limit not larger than 20%. If this result remains valid for fainter LBGs down to current observational limits, then the LBG population might be not sufficient to account for the entire photoionization budget at the redshifts considered here, with the exact details dependent upon the assumed ionizing background and QSO contribution thereto. It is possible that f(esc) depends on the UV luminosity of the galaxies, with fainter galaxies having higher f(esc), and estimates of f(esc) from a sample of faint LBGs from HUDF (i775 &lt;= 28.5) are in broad quantitative agreement with such a scenario.

The disk around AB Aur was imaged and resolved at 24.6 mu m using the Cooled Mid-infrared Camera and Spectrometer on the 8.2 m Subaru Telescope. The Gaussian full width at half-maximum of the source size is estimated to be 90 +/- 6 AU, indicating that the disk extends further out at 24.6 mu m than at shorter wavelengths. In order to interpret the extended 24.6 mu m image, we consider a disk with a reduced surface density within a boundary radius R(c), which is motivated by radio observations that suggest a reduced inner region within about 100 AU from the star. Introducing the surface density reduction factor f(c) for the inner disk, we determine that the best match with the observed radial intensity profile at 24.6 mu m is achieved with R(c) = 88 AU and f(c) = 0.01. We suggest that the extended emission at 24.6 mu m is due to the enhanced emission from a wall-like structure at the boundary radius (the inner edge of the outer disk), which is caused by a jump in the surface density at R(c). Such a reduced inner disk and geometrically thick outer disk structure can also explain the more point-like nature at shorter wavelengths. We also note that this disk geometry is qualitatively similar to a pre-transitional disk, suggesting that the AB Aur disk is in a pre-transitional disk phase.

In a deep image of the SSA22 field taken through a narrowband filter NB912 installed in the Subaru/Suprime-Cam, we have found the number density of the photometric Lyα emitter (LAE) candidates with LLyα &gt
3 × 1042 erg s-1 at z = 6.5 is a factor of 3-7 smaller than that found at the same redshift in the Subaru Deep field (SDF). There is a trend that more luminous LAE candidates are fewer. If we consider a scenario that a larger neutral fraction of intergalactic hydrogen, x HI, in the SSA22 field obscures a part of Lya emission, x HI in the SSA22 field should be about 2 times larger than that in the SDF, which is translated into xHI &lt
0.9 in the SSA22 at z = 6.5. © 2010 American Institute of Physics.

観測的宇宙論の大問題、宇宙再イオン化（宇宙再電離）に関して、銀河の電離光子放射スペクトルの新しい理論モデルを提案した。電離光子を放射する大質量星は、周囲の中性水素ガスを電離して、電離水素領域を形成する。その中では、陽子と電子の再結合により星雲電離光子が発生するが、その電離光子は「その場」で消費されると従来仮定されてきた。この仮定をはずし、より一般的に星雲電離光子の銀河外への脱出を初めて考慮すると、水素ライマン端のすぐ短波長に、星雲電離光子のスペクトルバンプが生じることを明らかにした。このスペクトルバンプは、若く（年齢100万年以内）、大質量（太陽の100倍程度）の超低金属星やゼロ金属星などの新しい指標として利用できる。

We have examined dust photoelectric heating in the intergalactic medium (IGM). The heating rate in a typical radiation field of the IGM is represented by Gamma(pe) = 1.2 x 10(-34) erg s(-1) cm(-3) (D/10(-4))(n(H)/10(-5) cm(-3))(4/3)(J(L)/10(-21) erg s(-1) cm(-2) Hz(-1) sr(-1))(2/3)(T/10(4) K)(-1/6), where D is the dust-to-gas mass ratio, n(H) is the hydrogen number density, J(L) is the mean intensity at the hydrogen Lyman limit of the background radiation, and T is the gas temperature, if we assume the new X-ray photoelectric yield model by Weingartner et al. (2006) and the dust size distribution in the Milky Way by Mathis et al. (1977). This heating rate dominates the HI and Hell photoionization heating rates when the hydrogen number density is less than similar to 10(-6) cm(-3) if D = 10(-4) which is 1% of that in the Milky Way, although the heating rate is a factor of 2-4 smaller than that with the old yield model by Weingartner and Draine (2001). The grain size distribution is very important. If only large (&gt;= 0.1 mu m) grains exist in the IGM, the heating rate is reduced by it factor of similar or equal to 5. Since dust heating is more efficient in a lower density medium relative to the photoionization heating, it may Cause all inverted temperature-density relation in the low-density IGM, as Suggested by Bolton et al. (2008). Finally, we have found that dust heating is not very important in the mean IGM before the cosmic reionization.

赤方偏移z=3.1（今から約100億年前）の宇宙で、ライマンαブロッブと呼ばれる巨大な銀河を発見した研究。この種の巨大銀河はこれまでに数十個が発見されているが、これまでその成因は謎に包まれていた。この研究では、この種の巨大銀河は銀河が特に密集した銀河の高密度領域でのみ形成されるということを、観測的に示した。

The temperature in the optically thick interior of protoplanetary discs is essential for the interpretation of millimetre observations of the discs, for the vertical structure of the discs, for models of the disc evolution and the planet formation, and for the chemistry in the discs. Since large icy grains have a large albedo even in the infrared, the effect of scattering of the diffuse radiation in the discs on the interior temperature should be examined. We have performed a series of numerical radiation transfer simulations, including isotropic scattering by grains with various typical sizes for the diffuse radiation as well as for the incident stellar radiation. We also have developed an analytic model including isotropic scattering to understand the physics concealed in the numerical results. With the analytic model, we have shown that the standard two-layer approach is valid only for grey opacity (i.e. grain size greater than or similar to 10 mu m) even without scattering. A three-layer interpretation is required for grain size less than or similar to 10 mu m. When the grain size is 0.1-10 mu m, the numerical simulations show that the isotropic scattering reduces the temperature of the disc interior. This reduction is nicely explained by the analytic three-layer model as a result of the energy loss by scatterings of the incident stellar radiation and of the warm diffuse radiation in the disc atmosphere. For grain size greater than or similar to 10 mu m (i.e. grey scattering), the numerical simulations show that the isotropic scattering does not affect the interior temperature. This is nicely explained by the analytic two-layer model; the energy loss by scattering in the disc atmosphere is exactly offset by the &apos;green-house effect&apos; due to the scattering of the cold diffuse radiation in the interior.

Knowing the amount of ionizing photons from young star-forming galaxies is of particular importance to understanding the reionization process. Here we report initial results of a Subaru/Suprime-Cam deep imaging observation of the SSA22 proto-cluster region at z = 3.09, using a special narrow-band filter to optimally trace ionizing radiation from galaxies at z similar to 3. The unique wide field-of-view of Suprime-Cam enabled us to search for ionizing photons from 198 galaxies (73 Lyman break galaxies (LBGs) and 125 Ly alpha emitters (LAEs)) with spectroscopically measured redshifts z similar or equal to 3.1. We detected ionizing radiation from 7 LBGs, as well as from 10 LAE candidates. Some of the detected galaxies show significant spatial offsets of ionizing radiation from nonionizing UV emission. For some LBGs the observed nonionizing UV to Lyman continuum flux density ratios are smaller than values expected from population synthesis models with a standard Salpeter initialmass function (IMF) with moderate dust attenuation (which is suggested from the observed UV slopes), even if we assume very transparent intergalactic medium along the sightlines of these objects. This implies an intrinsically bluer spectral energy distribution, e. g., that produced by a top-heavy IMF, for these LBGs. The observed flux density ratios of nonionizing UV to ionizing radiation of 7 detected LBGs range from 2.4 to 23.8 and the median is 6.6. The observed flux density ratios of the detected LAEs are even smaller than LBGs, if they are truly at z similar or equal to 3.1. We find that the median value of the flux density ratio for the detected LBGs suggests that their escape fractions are likely to be higher than 4%, if the Lyman continuum escape is isotropic. The results imply that some of the LBGs in the proto-cluster at z similar to 3 have escape fraction significantly higher than that of galaxies (in a general field) at z similar to 1 studied previously.

We have made a Monte Carlo simulation of the intergalactic absorption in order to model the Lyman continuum absorption, which is required to estimate the escape fraction of the Lyman continuum from distant galaxies. To input into the simulation, we derive an empirical distribution function of the intergalactic absorbers which reproduces recent observational statistics of the Lyman alpha forest, Lyman limit systems (LLSs) and damped Lyman alpha systems (DLAs) simultaneously. In particular, we assume a common functional form of the number evolution along the redshift for all types of absorbers. The Lyman series transmissions in our simulation reproduce the observed redshift evolution of the transmissions excellently, and the Lyman continuum transmission also agrees with an observed estimation which is still quite rare in the literature. The probability distribution of the Lyman alpha opacity in our simulation is lognormal with a tail towards a large opacity. This tail is produced by DLAs. The probability distribution of the Lyman continuum opacity in our simulation also shows a broad tail towards a large opacity. This tail is produced by LLSs. Because of the rarity of LLSs, we have a chance to have a clean line of sight in the Lyman continuum even for z similar to 4 with a probability of about 20 per cent. Our simulation expects a good correlation between the Lyman continuum opacity and the Lyman alpha opacity, which may be useful to estimate the former from the latter for an individual line of sight.

We discuss how we obtain the spatial distribution of ice on the surface of the circumstellar disk around young stars. Ice in the disks plays a very important role in various issues, for instance, on the disk structure, on planet formation, on an isotopic anomaly in meteorites, and on the origin of the oceans on Earth. Therefore, spatially resolved observations of the condensation/sublimation front of ice, the so-called snow line is strongly required. Here, we propose a new method for obtaining a spatially resolved snow line on circumstellar disks by observing a 3 mu m H2O ice feature in the scattered light. Based on radiative transfer considerations, we show that the feature is clearly imprinted in the spectrum of the scattered light from both optically thick and thin circumstellar disks. We also show that the scattered light and the H2O ice feature from protoplanetary disks are detectable and spatially resolvable with current instruments through an H2O narrowband filter around 3 Am. Finally, we present a diagnostics of disk dust properties on K - H2O and K - L' two-color diagram.

We analyse the attenuation properties of a sample of ultraviolet (UV) selected galaxies, with the use of the spectrophotometric model GRASIL. In particular, we focus on the relation between dust attenuation and the reddening in the UV spectral region. We show that a realistic modelling of geometrical distribution of dust and the different population of stars can explain the UV reddening of normal spiral galaxies also with a standard Milky Way dust. Our results clearly underline that it is fundamental to take into account that younger stars suffer a higher attenuation than older stars (the age-dependent extinction) because stars are born in more-than-average dusty environments. In this work, we also find that the concentration of young stars on the galactic plane of spirals has a relevant impact on the expected UV colours, impact that has not been explored before this paper. Finally, we discuss the role of the initial mass function (IMF) in shaping the relation between UV reddening and dust attenuation, and we show that a Kroupa IMF is more consistent with observed data than the classical Salpeter IMF.

The thermal and fragmentation properties of star forming clouds have important consequences on the corresponding characteristic stellar mass. The initial composition of the gas within these clouds is a record of the nucleosynthetic products of previous stellar generations. In this paper, we present a model for the evolution of star forming clouds enriched by metals and dust from the first supernovae (SNe), resulting from the explosions of metal-free progenitors with masses in the range 12-30M(circle dot) and 140-260M(circle dot). Using a self-consistent approach, we show that: (i) metals depleted on to dust grains play a fundamental role, enabling fragmentation to solar or subsolar mass scales already at metallicities Z(cr) = 10(-6) Z(circle dot); (ii) even at metallicities as high as 10(-2) Z(circle dot), metals diffused in the gas phase lead to fragment mass scales which are greater than or similar to 100M(circle dot); (iii) C atoms are strongly depleted on to amorphous carbon grains and CO molecules so that CII plays a minor role in gas cooling, leaving OI as the main gas-phase cooling agent in low-metallicity clouds. These conclusions hold independently of the assumed SN progenitors and suggest that the onset of low-mass star formation is conditioned to the presence of dust in the parent clouds.

星間塵は紫外線を強く吸収・散乱するので、紫外線スペクトルにその特徴が現れる。ところが、近傍円盤銀河の紫外線観測スペクトルには、銀河系の星間塵に見られる特徴が見られないことが近年明らかになってきた。この問題を、現実的な星間塵分布と詳細な輻射輸送シミュレーションにより調べ、観測された紫外線スペクトルと銀河系の星間塵は矛盾しないことを示した。

We present results of VLT/FORS2 spectroscopy of galaxies at z similar to 3 in the Hubble Deep Field - South (HDF-S). A sample of galaxies was drawn from the photometric redshift catalogue based on the HST/WFPC2 optical images and the deep near-infrared images obtained with VLT/ISAAC as a part of the Faint Infrared Extragalactic Survey ( FIRES) project. We selected galaxies with photometric redshift between 2.5 and 4. Most of the selected galaxies are bright in rest-frame UV wavelengths and satisfy color selection criteria of Lyman break galaxies (LBGs) at z similar to 3. The number of target galaxies with I-AB &lt;= 25.0 was 15. We identified new 5 firm and 2 probable redshifts in addition to confirmation of 6 previously known galaxies at z similar to 3. We found that 6 among these 13 galaxies lie in a quite narrow redshift range at z = 2.80 +/- 0.01. Their spatial distribution is fairly concentrated and is at the edge of the HDF-S field, suggesting the possible existence of larger galaxy clustering. We examined stellar populations of the galaxies with spectroscopic redshifts through comparisons of their optical and near-infrared photometry data with template spectra generated by a population synthesis code. The ages from the onset of star formation for these star-forming galaxies with I &lt;= 25.0 are typically 50- 200 Myr, and their stellar masses are between (0.5- 5) x 10(10) M-., consistent with previous studies. We also compared these SED fitting results with those for "distant red galaxies" (DRGs) at z &gt; 2 discovered by FIRES. DRGs have larger stellar masses, higer dust attenuation than our UV-luminous LBG sample, and their star formation rates are often comparable to LBGs. These trends suggest that majority of the DRGs are indeed the most massive systems at that redshift and are still in the active star-forming phase. Unless the number density of DRGs is much smaller than LBGs, estimates based on a UV selected sample could miss substantial part of stellar mass density at z similar to 3.

We have performed narrow-band imaging observations with the Very Large Telescope, aimed at detecting the Lyman continuum (LC) flux escaping from galaxies at z ∼ 3. We do not find any significant LC flux from our sample of two galaxies in the Hubble Deep Field South, at z = 3.170 and 3.275. The corresponding lower limits on the F1400/F900 flux density (per Hz) ratio are 15.6 and 10.2 (3-σ confidence level). After correction for the intergalactic hydrogen absorption, the resulting limits on the relative escape fraction of the LC are compared with those obtained by different approaches, at similar or lower redshifts. One of our two objects has a relative escape fraction lower than the detection reported by Steidel et al. in a composite spectrum of z ∼ 3 galaxies. A larger number of objects is required to reach a significant conclusion. Our comparison shows the potential of narrow-band imaging for obtaining the best limit on the relative escape fraction at z ∼ 3. Stacking a significant number of galaxies observed through a narrow-band filter would provide constraint on the galactic contribution to the cosmic reionization. © ESO 2005.

We have performed narrow-band imaging observations with the Very Large Telescope, aimed at detecting the Lyman continuum (LC) flux escaping from galaxies at z similar to 3. We do not find any significant LC flux from our sample of two galaxies in the Hubble Deep Field South, at z = 3.170 and 3.275. The corresponding lower limits on the F-1400/F-900 flux density ( per Hz) ratio are 15.6 and 10.2 ( 3-sigma confidence level). After correction for the intergalactic hydrogen absorption, the resulting limits on the relative escape fraction of the LC are compared with those obtained by different approaches, at similar or lower redshifts. One of our two objects has a relative escape fraction lower than the detection reported by Steidel et al. in a composite spectrum of z similar to 3 galaxies. A larger number of objects is required to reach a significant conclusion. Our comparison shows the potential of narrow-band imaging for obtaining the best limit on the relative escape fraction at z similar to 3. Stacking a significant number of galaxies observed through a narrow-band filter would provide constraint on the galactic contribution to the cosmic reionization.

We investigate the attenuation law seen through an interstellar medium (ISM) with clumpy spatial distributions of stars and dust. The clumpiness of the dust distribution is introduced by a multiphase ISM model. We solve a set of radiative transfer equations with multiple anisotropic scatterings through the clumpy ISM in a one-dimensional plane-parallel geometry by using the mega-grain approximation, in which dusty clumps are regarded as very large particles (i.e. mega-grains). The clumpiness of the stellar distribution is introduced by the youngest stars embedded in the clumps. We assume a smooth spatial distribution for older stars. The youngest stars are surrounded by denser dusty gas and suffer stronger attenuation than diffuse older stars (i.e. age-selective attenuation). The apparent attenuation law is a composite of the attenuation laws for the clumpy younger stars and for the diffuse older stars with a luminosity weight. In general, the stellar population dominating the luminosity changes from older stars to younger stars as the wavelength decreases. This makes the attenuation law steep; the composite attenuation rapidly increases from small attenuation for older stars at a long wavelength to large attenuation for younger stars at a short wavelength. The resultant attenuation law of normal disc galaxies is expected to be much steeper than that of starburst galaxies observed by Calzetti et al. Finally, the Calzetti attenuation law is regarded as a special case with a large density in our framework.

The attenuation law through the clumpy interstellar medium (ISM) in disk galaxies is investigated. I adopted the mega-grain approximation, in which dusty clumps are regarded as very large particles (i.e. mega-grains), to treat the ISM dumpiness in a 1-D plane-parallel radiative transfer with multiple anisotropic scatterings. Further, a physical model of the dumpiness was introduced as an extention of the multi-phase ISM model. In this framework, the attenuation law is determined by three physical quantities in the ISM: the mean gas density, the mean pressure, and the dust-to-gas ratio. I found that the attenuation law of normal disk galaxies is much steeper than that of starburst galaxies observed by Calzetti et al.

We estimate a gamma-ray burst (GRB) formation rate based on the new relation between the spectral peak energy (E-p) and the peak luminosity. The new relation is derived by combining the data of E-p and the peak luminosities by BeppoSAX and BATSE, and it looks considerably tighter and more reliable than the relations suggested by the previous works. Using the new E-p-luminosity relation, we estimate redshifts of the 689 GRBs without known distances in the BATSE catalog and derive a GRB formation rate as a function of the redshift. For the redshift range of 0 less than or equal to z less than or equal to 2, the GRB formation rate increases and is well correlated with the star formation rate, while it keeps constant toward z similar to 12. We also discuss the luminosity function and the redshift dependence of the intrinsic luminosity ( luminosity evolution).

In this paper we examine the allowed amount of intergalactic (IG) dust, which is constrained by extinction and reddening of distant Type Ia supernovae (SNe Ia) and the thermal history of the intergalactic medium (IGM) affected by dust photoelectric heating. Based on the observational cosmic star formation history, we find an upper bound of chi, the mass ratio of the IG dust to the total metal in the Universe, as &gt;chiless than or similar to0.1 for 10 Angstromless than or similar toaless than or similar to0.1 mum and chiless than or similar to0.1(a/0.1 mum) for 0.1less than or similar toaless than or similar to1 mum, where a is a characteristic grain size of the IG dust. This upper bound of chisimilar to 0.1 suggests that the dust-to-metal ratio in the IGM is smaller than the current Galactic value. The corresponding allowed density of the IG dust increases from similar to10(-34) g cm(-3) at z=0 to similar to10(-33) g cm(-3) at zsimilar to1, and keeps almost the value toward higher redshift. This causes IG extinction of less than or similar to0.2 mag at the observer's B band for zsimilar to1 sources and that of less than or similar to1 mag for higher redshift sources. Furthermore, if (B-V)similar to0.1 mag at the observer's frame against zgreater than or similar to1 sources is detected, we can conclude that a typical size of the IG dust is less than or similar to100 Angstrom. The signature of the 2175-Angstrom feature of small graphite may be found as a local minimum at zsimilar to2.5 in a plot of the observed E(B-V) as a function of the source redshift. Finally, the IGM mean temperature at zless than or similar to1 can be still higher than 10(4) K, provided the size of the IG dust is less than or similar to100 Angstrom.

We discuss a way to study the cosmic reionization history using near-infrared (NIR) observations of the afterglows of high-redshift (5less than or similar tozless than or similar to25) gamma-ray bursts (GRBs) that will be detected by the Swift satellite. In principle, details of the cosmic reionization history should be imprinted in the NIR spectra of GRB afterglows. However, spectroscopy with a space telescope is required to obtain such information for very high redshifts (zgreater than or similar to15) unless the neutral fraction of the high-z universe is less than 10(-6). The broadband photometry has higher sensitivity than the spectroscopy, so that NIR photometric follow-up of GRB afterglows is very promising for examining cosmic reionization history. A few minutes exposure with a 8 m class ground-based telescope of the afterglows of the high-z GRBs will reveal how many times reionization occurred in the universe.

We propose a method for examining the cosmic reionization history by using near-infrared (NIR) colors of afterglows of high redshift (5 &lt; z &lt; 25) gamma-ray bursts (GRBs) that will be detected by the Swift satellite. The broad-band photometry has a much higher sensitivity than that of the spectroscopy. A prompt NIR photometric follow-up of the high-z GRB afterglows will reveal how many times the reionization occurred in the universe.

This paper investigates the evolution of the dust-to-metal ratio in galaxies based on a simple evolution model for the amount of metal and dust with infall. We take into account grain formation in stellar mass-loss gas, grain urowth bv the accretion of metallic atoms in a cold dense cloud, and grain destruction by SN shocks. Especially, we propose that the accretion efficiency is independent of the star-formation history. This predicts various evolutionary tracks in the metallicity (Z)-dust-to-gas ratio (D) plane depending on the star-formation history. In this framework, the observed linear Z-D relation of nearby spiral galaxies can be interpreted as a sequence of a constant galactic age. We emphasize that an observational study of the Z-D relation of galaxies at z similar to 1 is very useful to constrain the efficiencies of dust growth and destruction. We also suggest that the Lyman break galaxies at z similar to 3 have a very low dust-to-metal ratio, typically less than or similar to 0.1. Although the effect of infall on the evolutionary tracks in the Z-D plane is quite small. the dispersion of the infall rate can disturb the Z-D relation with a constant galactic age.

This letter investigates the amount of dust in the intergalactic medium (IGM). The dust photoelectric heating can be the most efficient heating mechanism in the IGM where the density is very small and there are a lot of hard ultraviolet photons. Comparing the observational thermal history of IGM with a theoretical one taking into account the dust photoelectric heating, we can put an upper limit on the dust-to-gas ratio, D, in the IGM. As the rate of the dust photoelectric heating depends on the size of dust, we find the following results: if the grain size is greater than or similar to100 Angstrom, D at z similar to 3 is less than or similar to1/100 Galactic value corresponding to Omega(dust)(IGM)less than or similar to10(-5). On the other hand, if the grain size is as small as similar to10 Angstrom, D is less than or similar to1/1000 Galactic value corresponding to Omega(dust)(IGM)less than or similar to10(-6).

We examine types of galaxies the conversion formula from dust infrared (IR) luminosity into the star formation rate (SFR) derived by R. C. Kennicutt is applicable to. The ratio of the observed IR luminosity L-IR, to the intrinsic bolometric luminosity of the newly (less than or similar to10 Myr) formed stars, L-SF, of a galaxy can be determined LSF by a mean dust opacity in the interstellar medium and the activity of the current star formation. We find that the area given by these parameters, 0.5 less than or equal to L-IR/L-SF less than or equal to 2.0, is very large, and many nearby normal and active star-forming galaxies really fall in this area. It results from offsetting two effects of a small dust opacity and a large cirrus contribution of normal galaxies relative to starburst galaxies on the conversion of the stellar emission into the dust IR emission. In conclusion, the SFR determined from the IR luminosity under the assumption of L-IR = L-SF, like Kennicutt's, is reliable within a factor of 2 for all galaxies except for dust-rich but quiescent galaxies and extremely dust-poor galaxies.

We discuss the dust distribution within photoionized regions. Assuming a geometry with a central dust cavity, which is strongly suggested by the literature, we can estimate the cavity radius from the ratio of the infrared and radio fluxes by using a simple transfer model of Lyman continuum photons. We apply the method to a sample of the Galactic H II regions. The estimated typical radius of the dust cavity of the Galactic compact H II regions is about 30% of the Stromgren radius. Taking into account uncertainties in both the observational data and the model, we can reject a dust distribution lacking a central cavity. Therefore, the dust cavity model is supported independently of the previous works. We discuss the formation mechanism of such a dust cavity and its detectability by present and future infrared facilities.

We examine Lyman continuum extinction (LCE) in H II regions by comparing infrared fluxes of 49 H II regions in the Galaxy, M31, M33, and the Large Megellanic Cloud with estimated production rates of Lyman continuum photons. A typical fraction of Lyman continuum photons that contribute to hydrogen ionization in the H II regions of three spiral galaxies is less than or similar to 50%. The fraction may become smaller as the metallicity (or dust-to-gas ratio) increases. We examine the LCE effect on estimated star formation rates of galaxies. The correction factor for the Galactic dust-to-gas ratio is 2-5.

We reexamine the effect of Lyman continuum (lambda less than or equal to 912 Angstrom )extinction (LCE) by dust in H II regions in detail and discuss how it affects the estimation of the global star formation rate (SFR) of galaxies. To clarify the first issue, we establish two independent methods for estimating a parameter of LCE (f), which is defined as the fraction of Lyman continuum photons contributing to hydrogen ionization in an H II region. One of those methods determines f from the set of Lyman continuum flux, electron density, and metallicity. In the framework of this method, as the metallicity and/or the Lyman photon flux increase, f is found to decrease. The other method determines f from the ratio of infrared flux to Lyman continuum flux. Importantly, we show that f less than or similar to 0.5 via both methods in many H II regions of the Galaxy. Thus, it establishes that dust in such H II regions absorbs significant amount of Lyman continuum photons directly. To examine the second issue, we approximate f to a function of only the dust-to-gas mass ratio (i.e., metallicity), assuming a parameter fit for the Galactic H II regions. We find that a characteristic (f) over cap, which is defined as f averaged over a galaxywide scale, is 0.3 for the nearby spiral galaxies. This relatively small (f) over cap indicates that a typical increment factor due to LCE for estimating the global SFR (1/(f) over cap) is large (similar to3) for the nearby spiral galaxies. Therefore, we conclude that the effect of LCE is not negligible relative to other uncertainties of estimating the SFR of galaxies.

Infrared (IR) dust emission from galaxies is frequently used as an indicator of star formation rate (SFR). However, the effect of the dust-to-gas ratio (i.e., amount of the dust) on the conversion law from IR luminosity to SFR has not so far been considered. Then, in this paper, we present a convenient analytical formula including this effect. In order to obtain the dependence on the dust-to-gas ratio, we extend the formula derived in our previous paper, in which a theoretical formula converting IR luminosity to SFR was derived. That formula was expressed as SFR/(M. yr(-1)) = {3.3 10-(10) (1-eta)/(0.4 - 0.2 + 0.6 epsilon)}(L-IR/L.), where f is the fraction of ionizing photons absorbed by hydrogen, epsilon is the efficiency of dust absorption for nonionizing photons, eta is the cirrus fraction of observed dust luminosity, and L-IR is the observed luminosity of dust emission in the 8-1000-mum range. Our formula explains the IR excess of the Galaxy and the Large Magellanic Cloud. In the current paper, especially, we present the metallicity dependence of our conversion law between SFR and LIR This is possible since both f and epsilon can be estimated via the dust-to-gas ratio, which is related to metallicity. We have confirmed that the relation between the metallicity and the dust-to-gas ratio is applied to both giant and dwarf galaxies. Finally, we apply the result to the cosmic star formation history. We find that the comoving SFR at z similar to 3 calculated from previous empirical formulae is underestimated by a factor of 4-5.

We investigate the structure of the molecular cloud complexes (MCCs) as a group of several giant molecular clouds (GMCs) in the Galaxy. We then find that the mass-size relation which has been reported for the GMCs is well-established even for very large MCCs, whose sizes are about 1 kpc. Since the horizontal size of the MCCs is larger than the thickness of the galactic disk, we can no longer consider the MCCs to be spherical. Thus, we construct a structural model of the MCCs, adopting a rectangular-solid geometry. As a result, our model explains the observed mass-size relation of the MCCs very well. From the estimated external pressure around the MCCs, we find that they are in a rough pressure balance with the interstellar medium. Moreover, we find there is an observational deficiency of the MCCs with a large size and surface density. We thus suggest that the external pressure has a significant effect on the structure and evolution of the MCCs. We also discuss the effect of H II regions in the MCCs.

It has been reported recently that there are some early-type spiral (Sa-Sab) galaxies with evident star-forming regions that concentrate in their own central 1 kpc. In such central region, is the mechanism of the star formation distinct from that in disks of spiral galaxies? To discover this, we estimate the star formation efficiency (SFE) in this central 1 kpc star-forming region of some early-type spiral galaxies, taking account of the condition required for this 1 kpc region to be self-gravitating. Using two indicators of the present star formation rate (H alpha and infrared luminosity), we estimate the SFE to a few percent. This is equivalent to the observational SFE in the disks of late-type spiral (Sb-) galaxies. This coincidence may support the universality of the mean SFE of spiral galaxies reported in the recent studies, that is, we find no evidence of a distinct mechanism of the star formation in the central 1 kpc region of early-type galaxies. Also, we examine the structure of the central star-forming region and discuss a method for estimating the mass of star-forming regions.