Population Of Massive Galaxies Research Articles

Obscured star formation in clusters at z = 1.6–2.0: massive galaxy formation and the reversal of the star formation–density relation

ABSTRACT Clusters of galaxies at z $\mathrel {\gtrsim }$ 1 are expected to be increasingly active sites of star formation. To test this, an 850 $\mu$m survey was undertaken of eight clusters at z = 1.6–2.0 using SCUBA-2 on the James Clerk Maxwell Telescope. Mid-infrared properties were used to identify 53 probable counterparts to 45 SCUBA-2 sources with colours that suggested they were cluster members. This uncovered a modest overdensity of 850 $\mu$m sources, with far-infrared luminosities of LIR ≥ 1012 L⊙ (SFR $\mathrel {\gtrsim }$ 100 M⊙ yr−1) and colours consistent with being cluster members, of a factor of 4 ± 1 within the central 1 Mpc radius of the clusters. The submillimetre photometry of these galaxies was used to estimate the total cluster star formation rates. These showed that the mass-normalized rates in the clusters are two orders of magnitude higher than in local systems, evolving as (1 + z)5.5 ± 0.6. This rapid evolution means that the mass-normalized star formation rates in these clusters matched that of average haloes in the field at z ∼ 1.8 ± 0.2 marking the epoch where the local star formation–density relation reverses in massive haloes. The estimated stellar masses of the cluster submillimetre galaxies suggests that their descendants will be amongst the most massive galaxies in z ∼ 0 clusters. This reinforces the suggestion that the majority of the massive early-type galaxy population in z ∼ 0 clusters were likely to have formed at z $\mathrel {\gtrsim }$ 1.5–2 through very active, but dust-obscured, starburst events.

On the Existence, Rareness, and Uniqueness of Quenched H i-rich Galaxies in the Local Universe

Using data from ALFALFA, xGASS, H i-MaNGA, and the Sloan Digital Sky Survey (SDSS), we identify a sample of 47 “red but H i-rich” (RR) galaxies with near-UV (NUV) − r > 5 and unusually high H i-to-stellar mass ratios. We compare the optical properties and local environments between the RR galaxies and a control sample of “red and H i-normal” (RN) galaxies that are matched in stellar mass and color. The two samples are similar in the optical properties typical of massive red (quenched) galaxies in the local Universe. The RR sample tends to be associated with slightly lower-density environments and has lower clustering amplitudes and smaller neighbor counts at scales from several hundred kiloparsecs to a few megaparsecs. The results are consistent with the RR galaxies being preferentially located at the center of low-mass halos, with a median halo mass ∼1012 h −1 M ⊙ compared to ∼1012.5 h −1 M ⊙ for the RN sample. This result is confirmed by the SDSS group catalog, which reveals a central fraction of 89% for the RR sample, compared to ∼60% for the RN sample. If assumed to follow the H i size–mass relation of normal galaxies, the RR galaxies have an average H i-to-optical radius ratio of R HI/R 90 ∼ 4, four times the average ratio for the RN sample. We compare our RR sample with similar samples in previous studies, and quantify the population of RR galaxies using the SDSS complete sample. We conclude that the RR galaxies form a unique but rare population, accounting for only a small fraction of the massive quiescent galaxy population. We discuss the formation scenarios of the RR galaxies.

A population of faint, old, and massive quiescent galaxies at 3

Here we present a sample of 12 massive quiescent galaxy candidates at z∼3-4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z\\sim 3-4$$\\end{document} observed with the James Webb Space Telescope (JWST) Near Infrared Spectrograph (NIRSpec). These galaxies were pre-selected from the Hubble Space Telescope imaging and 10 of our sources were unable to be spectroscopically confirmed by ground based spectroscopy. By combining spectroscopic data from NIRSpec with multi-wavelength imaging data from the JWST Near Infrared Camera (NIRCam), we analyse their stellar populations and their formation histories. We find that all of our galaxies classify as quiescent based on the reconstruction of their star formation histories but show a variety of quenching timescales and ages. All our galaxies are massive (∼0.1-1.2×1011\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim 0.1-1.2\ imes 10^{11}$$\\end{document} M⊙\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_\\odot$$\\end{document}), with masses comparable to massive galaxies in the local Universe. We find that the oldest galaxy in our sample formed ∼1.0×1011\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim 1.0\ imes 10^{11}$$\\end{document} M⊙\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_\\odot$$\\end{document} of mass within the first few hundred million years of the Universe and has been quenched for more than a billion years by the time of observation at z∼3.2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z\\sim 3.2$$\\end{document} (∼2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim 2$$\\end{document} billion years after the Big Bang). Our results point to very early formation of massive galaxies requiring a high conversion rate of baryons to stars in the early Universe.

Stellar populations of massive early-type galaxies observed by MUSE

ABSTRACT Stellar population studies of massive early-type galaxies (ETGs) suggest that the stellar initial mass function may not be universal. In particular, the centres of ETGs seem to contain an excess of low-mass dwarf stars compared to our own Galaxy. Through high-resolution data from MUSE (Multi Unit Spectroscopic Explorer), we carry out a detailed study of the stellar populations of eight massive ETGs. We use full spectrum fitting to determine ages, element abundances, and initial mass function (IMF) slopes for spatially binned spectra. We measure flat gradients in age and [Mg/Fe] ratio, as well as negative gradients in metallicity and [Na/Fe]. We detect IMF gradients in some galaxies, with the centres hosting bottom-heavy IMFs and mass excess factors between 1.5 and 2.5 compared to a Kroupa IMF. The IMF slope below 0.5 M$_\odot$varies for our galaxy sample between 1 and 2.8, with negative radial gradients, while the IMF slope between 0.5 and 1M$_\odot$ has a steep value of $\sim$3 with mildly positive gradients for most galaxies. For M87, we find excellent agreement with the dynamical mass-to-light ratio (M/L) as a function of radius. For the other galaxies, we find systematically higher M/L from stellar populations compared to orbit-based dynamical analysis of the same data. This discrepancy increases with NaI strength, suggesting a combination of calibration issues of this line and correlated uncertainties.

An enhanced abundance of bright galaxies in protocluster candidates at z ∼ 3–5

ABSTRACT We present a protocluster search covering z ∼ 3 to z ∼ 5 based on the combination of the Hyper SuprimeCam Subaru Strategic Programme and the CFHT Large Area U-band Deep Survey. We identify about 30 protocluster candidates per unit redshift over the $\sim 25\, \mathrm{deg^2}$ area of the Deep/UltraDeep layer. Protocluster candidates are selected as regions with a significantly enhanced surface density of dropout galaxies. With this large sample, we characterize the properties of their individual member galaxies. We compare the number counts of dropout galaxies in protocluster candidates with that of coeval field galaxies. Rest-frame ultraviolet (UV) bright galaxies are overabundant in protocluster candidates, a trend seen across the full redshift range studied. We do not find evidence for their spatial distribution within protocluster candidates to be distinct from their fainter counterparts, nor for their UV colour to be different from that of field galaxies with the same brightness. Cosmological simulations predict this bright-end excess, with the main cause being a richer population of massive galaxies, with only a minor contribution from an enhancement in star formation activity (and therefore UV emission) at fixed mass. U-to-K SED modelling of our observed samples supports this interpretation. This environmental differentiation in number counts is already in place at z ∼ 5, with no significant redshift dependence over the range in lookback times probed . These observational results and model predictions suggest that the cosmic clock is ahead in high-density environments.

JWST CEERS probes the role of stellar mass and morphology in obscuring galaxies

In recent years, observations have uncovered a population of massive galaxies that are invisible or very faint in deep optical/near-infrared (near-IR) surveys but brighter at longer wavelengths. However, the nature of these optically dark or faint galaxies (OFGs; one of several names given to these objects) is highly uncertain. In this work, we investigate the drivers of dust attenuation in the JWST era. In particular, we study the role of stellar mass, size, and orientation in obscuring star-forming galaxies (SFGs) at 3 < z < 7.5, focusing on the question of why OFGs and similar galaxies are so faint at optical/near-IR wavelengths. We find that stellar mass is the primary proxy for dust attenuation, among the properties studied. Effective radius and axis ratio do not show a clear link with dust attenuation, with the effect of orientation being close to random. However, there is a subset of highly dust attenuated (AV > 1, typically) SFGs, of which OFGs are a specific case. For this subset, we find that the key distinctive feature is their compact size (for massive systems with log(M*/M⊙) > 10); OFGs exhibit a 30% smaller effective radius than the average SFG at the same stellar mass and redshift. On the contrary, OFGs do not exhibit a preference for low axis ratios (i.e., edge-on disks). The results in this work show that stellar mass is the primary proxy for dust attenuation and compact stellar light profiles behind the thick dust columns obscuring typical massive SFGs.

DESI Survey Validation Spectra Reveal an Increasing Fraction of Recently Quenched Galaxies at z ∼ 1

We utilize ∼17,000 bright luminous red galaxies (LRGs) from the novel Dark Energy Spectroscopic Instrument Survey Validation spectroscopic sample, leveraging its deep (∼2.5 hr galaxy−1 exposure time) spectra to characterize the contribution of recently quenched galaxies to the massive galaxy population at 0.4 < z < 1.3. We use Prospector to infer nonparametric star formation histories and identify a significant population of recently quenched galaxies that have joined the quiescent population within the past ∼1 Gyr. The highest-redshift subset (277 at z > 1) of our sample of recently quenched galaxies represents the largest spectroscopic sample of post-starburst galaxies at that epoch. At 0.4 < z < 0.8, we measure the number density of quiescent LRGs, finding that recently quenched galaxies constitute a growing fraction of the massive galaxy population with increasing look-back time. Finally, we quantify the importance of this population among massive ( > 11.2) LRGs by measuring the fraction of stellar mass each galaxy formed in the gigayear before observation, f 1 Gyr. Although galaxies with f 1 Gyr > 0.1 are rare at z ∼ 0.4 (≲0.5% of the population), by z ∼ 0.8, they constitute ∼3% of massive galaxies. Relaxing this threshold, we find that galaxies with f 1 Gyr > 5% constitute ∼10% of the massive galaxy population at z ∼ 0.8. We also identify a small but significant sample of galaxies at z = 1.1–1.3 that formed with f 1 Gyr > 50%, implying that they may be analogs to high-redshift quiescent galaxies that formed on similar timescales. Future analysis of this unprecedented sample promises to illuminate the physical mechanisms that drive the quenching of massive galaxies after cosmic noon.

Unveiling the nature of infrared bright, optically dark galaxies with early JWST data

ABSTRACT Over the last few years, both Atacama Large Millimeter/submillimeter Array (ALMA) and Spitzer observations have revealed a population of likely massive galaxies at z &amp;gt; 3 that was too faint to be detected inHubble Space Telescope(HST) rest-frame ultraviolet imaging. However, due to the very limited photometry for individual galaxies, the true nature of these so-called HST-dark galaxies has remained elusive. Here, we present the first sample of such galaxies observed with very deep, high-resolution NIRCam imaging from the Early Release Science programme CEERS. 30 HST-dark sources are selected based on their red colours across 1.6–4.4 $\mu$m. Their physical properties are derived from 12-band multiwavelength photometry, including ancillary HST imaging. We find that these galaxies are generally heavily dust-obscured (AV ∼ 2 mag), massive (log (M/M⊙) ∼ 10), star-forming sources at z ∼ 2−8 with an observed surface density of ∼0.8 arcmin−2. This suggests that an important fraction of massive galaxies may have been missing from our cosmic census at z &amp;gt; 3 all the way into the Epoch of Reionization. The HST-dark sources lie on the main sequence of galaxies and add an obscured star formation rate density of $\mathrm{3.2^{+1.8}_{-1.3} \times 10^{-3} \,{\rm M}_{\odot }\,yr^{-1}\,Mpc^{-3}}$ at z ∼ 7, showing likely presence of dust in the Epoch of Reionization. Our analysis shows the unique power of JWST to reveal this previously missing galaxy population and to provide a more complete census of galaxies at z = 2−8 based on rest-frame optical imaging.

CEERS Key Paper. II. A First Look at the Resolved Host Properties of AGN at 3 < z < 5 with JWST

We report on the host properties of five X-ray-luminous active galactic nuclei (AGN) identified at 3 < z < 5 in the first epoch of imaging from the Cosmic Evolution Early Release Science Survey. Each galaxy has been imaged with the JWST Near-Infrared Camera, which provides rest-frame optical morphologies at these redshifts. We also derive stellar masses and star formation rates for each host by fitting its spectral energy distribution using a combination of galaxy and AGN templates. We find that three of the AGN hosts have spheroidal morphologies, one is a bulge-dominated disk, and one is dominated by pointlike emission. None are found to show strong morphological disturbances that might indicate a recent interaction or merger event. When compared to a sample of mass-matched inactive galaxies, we find that the AGN hosts have morphologies that are less disturbed and more bulge-dominated. Notably, all four of the resolved hosts have rest-frame optical colors consistent with a quenched or poststarburst stellar population. The presence of AGN in passively evolving galaxies at z > 3 is significant because a rapid feedback mechanism is required in most semianalytic models and cosmological simulations to explain the growing population of massive quiescent galaxies observed at these redshifts. Our findings show that AGN can continue to inject energy into these systems after their star formation is curtailed, potentially heating their halos and preventing renewed star formation. Additional observations will be needed to determine what role this feedback may play in helping to quench these systems and/or maintain their quiescent state.

A population of red candidate massive galaxies ~600 Myr after the Big Bang.

Galaxies with stellar masses as high as roughly 1011 solar masses have been identified1-3 out to redshifts z of roughly 6, around 1 billion years after the Big Bang. It has been difficult to find massive galaxies at even earlier times, as the Balmer break region, which is needed for accurate mass estimates, is redshifted to wavelengths beyond 2.5 μm. Here we make use of the 1-5 μm coverage of the James Webb Space Telescope early release observations to search for intrinsically red galaxies in the first roughly 750 million years of cosmic history. In the survey area, we find six candidate massive galaxies (stellar mass more than 1010 solar masses) at 7.4 ≤ z ≤ 9.1, 500-700 Myr after the Big Bang, including one galaxy with a possible stellar mass of roughly 1011 solar masses. If verified with spectroscopy, the stellar mass density in massive galaxies would be much higher than anticipated from previous studies on the basis of rest-frame ultraviolet-selected samples.

Galaxy populations in the most distant SPT-SZ clusters

We investigate structural properties of massive galaxy populations in the central regions (&lt; 0.7 r500) of five very massive (M200 &gt; 4 × 1014 M⊙), high-redshift (1.4 ≲ z ≲ 1.7) galaxy clusters from the 2500 deg2 South Pole Telescope Sunyaev Zel’dovich effect (SPT-SZ) survey. We probe the connection between galaxy structure and broad stellar population properties at stellar masses of log(M/M⊙) &gt; 10.85. We find that quiescent and star-forming cluster galaxy populations are largely dominated by bulge- and disk-dominated sources, respectively, with relative contributions being fully consistent with those of field counterparts. At the same time, the enhanced quiescent galaxy fraction observed in these clusters with respect to the coeval field is reflected in a significant morphology-density relation, with bulge-dominated galaxies already clearly dominating the massive galaxy population in these clusters at z ∼ 1.5. At face value, these observations show no significant environmental signatures in the correlation between broad structural and stellar population properties. In particular, the Sersic index and axis ratio distribution of massive, quiescent sources are consistent with field counterparts, in spite of the enhanced quiescent galaxy fraction in clusters. This consistency suggests a tight connection between quenching and structural evolution towards a bulge-dominated morphology, at least in the probed cluster regions and galaxy stellar mass range, irrespective of environment-related processes affecting star formation in cluster galaxies. We also probe the stellar mass–size relation of cluster galaxies, and find that star-forming and quiescent sources populate the mass–size plane in a manner largely similar to their field counterparts, with no evidence of a significant size difference for any probed sub-population. In particular, both quiescent and bulge-dominated cluster galaxies have average sizes at fixed stellar mass consistent with their counterparts in the field.

The first catalogue of spectroscopically confirmed red nuggets at z ∼ 0.7 from the VIPERS survey

Context. Red nuggets are a rare population of passive compact massive galaxies thought to be the first massive galaxies that formed in the Universe. First found at z ∼ 3, they are even less abundant at lower redshifts, and it is believed that with time they mostly transformed through mergers into today’s giant ellipticals. The red nuggets that managed to escape this fate can serve as unique laboratories to study the early evolution of massive galaxies. Aims. In this paper we aim to make use of the unprecedented statistical power of the VIMOS Public Extragalactic Redshift Survey to build the largest up-to-date catalogue of spectroscopically confirmed red nuggets at the intermediate redshift 0.5 &lt; z &lt; 1.0. Methods. Starting from a catalogue of nearly 90 000 VIPERS galaxies we selected sources with stellar masses Mstar &gt; 8 × 1010 M⊙ and effective radii Re &lt; 1.5 kpc. From these sources we selected red passive galaxies with old stellar populations based on colour–colour NUVrK diagram, star formation rate values, and verification of their optical spectra. Results. Verifying the influence of the limit of the source compactness on the selection, we found that the sample size can vary by up to two orders of magnitude, depending on the chosen criterion. Using one of the most restrictive criteria with additional checks on their spectra and passiveness, we spectroscopically identified only 77 previously unknown red nuggets. The resultant catalogue of 77 red nuggets is the largest such catalogue built based on the uniform set of selection criteria above the local Universe. The number density calculated on the final sample of 77 VIPERS passive red nuggets per comoving Mpc3 increases from 4.7 × 10−6 at z ∼ 0.61 to 9.8 × 10−6 at z ∼ 0.95, which is higher than values estimated in the local Universe, and lower than the values found at z &gt; 2. It fills the gap at intermediate redshift. Conclusions. A catalogue of red nuggets presented in this paper is a golden sample for future studies of this rare population of objects at intermediate redshift. In addition to covering a unique redshift range and careful selection of galaxies, the catalogue is spectroscopically identified.

An Elusive Population of Massive Disk Galaxies Hosting Double-lobed Radio-loud Active Galactic Nuclei

It is commonly accepted that radio-loud active galactic nuclei are hosted exclusively by giant elliptical galaxies. We analyze high-resolution optical Hubble Space Telescope images of a sample of radio galaxies with extended double-lobed structures associated with disk-like optical counterparts. After systematically evaluating the probability of chance alignment between the radio lobes and the optical counterparts, we obtain a sample of 18 objects likely to have genuine associations. The host galaxies have unambiguous late-type morphologies, including spiral arms, large-scale dust lanes among the edge-on systems, and exceptionally weak bulges, as judged by the low global concentrations, small global Sérsic indices, and low bulge-to-total light ratios (median B/T = 0.13). With a median Sérsic index of 1.4 and low effective surface brightnesses, the bulges are consistent with being pseudobulges. The majority of the hosts have unusually large stellar masses (median M * = 1.3 × 1011 M ⊙) and red optical colors (median g − r = 0.69 mag), consistent with massive, quiescent galaxies on the red sequence. We suggest that the black hole mass (stellar mass) plays a fundamental role in launching large-scale radio jets, and that the rarity of extended radio lobes in late-type galaxies is the consequence of the steep stellar mass function at the high-mass end. The disk radio galaxies have mostly Fanaroff–Riley type II morphologies yet lower radio power than sources of a similar type traditionally hosted by ellipticals. The radio jets show no preferential alignment with the minor axis of the galactic bulge or disk, apart from a possible mild tendency for alignment among the most disk-dominated systems.

The SCUBA-2 Cosmology Legacy Survey: the EGS deep field – III. The evolution of faint submillimetre galaxies atz&amp;lt; 4

ABSTRACTWe present a demographic analysis of the physical and morphological properties of $450/850~\mu \rm m$-selected galaxies from the deep observations of the SCUBA-2 Cosmology Legacy Survey in the Extended Groth Strip that are detected below the classical submillimetre-galaxy regime ($S_{850\, \mu \rm m}\lesssim 6~\rm mJy$ beam−1) and compare them with a sample of optically selected star-forming galaxies detected in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey in the same field. We derive the evolution of the main sequence of star-forming galaxies, finding a steeper specific star formation rate versus stellar mass at z &amp;gt; 2.5 than previous studies. Most faint submillimetre-galaxies fall within 3σ of the main sequence, but 40 per cent are classified as starbursts. Faint submillimetre galaxies have 50 per cent larger sizes at 2 &amp;lt; z &amp;lt; 3 than optically selected star-forming galaxies of the same mass range. This is also the redshift bin where we find the largest fraction of starbursts, and hence we could be witnessing merging processes, as confirmed by the preference for visual-morphology classifications of these systems as irregular disc galaxies and mergers. Both populations show an increment towards lower redshifts (z &amp;lt; 2) of their concentration in H-band morphology, but faint submillimetre galaxies on average show larger concentration values at later times. These findings support the claim that faint submillimetre galaxies are mostly a population of massive dust-obscured disc-like galaxies that develop larger bulge components at later epochs. While the similarities are great, the median sizes, starburst numbers, and H-band concentration of faint submillimetre galaxies differ from those of optically selected star-forming galaxies of the same stellar mass.

Supermassive black holes at high redshift are expected to be obscured by their massive host galaxies’ interstellar medium

We combine results from deep ALMA observations of massive (M* &gt; 1010 M⊙) galaxies at different redshifts to show that the column density of their interstellar medium (ISM) rapidly increases toward early cosmic epochs. Our analysis includes objects from the ASPECS and ALPINE large programs, as well as individual observations of z ∼ 6 quasar hosts. When accounting for non-detections and correcting for selection effects, we find that the median surface density of the ISM of the massive galaxy population evolves as ∼(1 + z)3.3. This means that the ISM column density toward the nucleus of a z &gt; 3 galaxy is typically &gt; 100 times larger than locally, and it may reach values as high as Compton-thick at z ≳ 6. Remarkably, the median ISM column density is on the same order of what is measured from X-ray observations of large active galactic nucleus (AGN) samples already at z ≳ 2. We have developed a simple analytic model for the spatial distribution of ISM clouds within galaxies, and estimate the total covering factor toward active nuclei when obscuration by ISM clouds on the host scale is added to that of parsec-scale circumnuclear material (the so-called torus). The model includes clouds with a distribution of sizes, masses, and surface densities, and also allows for an evolution of the characteristic cloud surface density with redshift, Σc, * ∝ (1 + z)γ. We show that, for γ = 2, such a model successfully reproduces the increase in the obscured AGN fraction with redshift that is commonly observed in deep X-ray surveys, both when different absorption thresholds and AGN luminosities are considered. Our results suggest that 80–90% of supermassive black holes in the early Universe (z &gt; 6 − 8) are hidden to our view, primarily by the ISM in their hosts. We finally discuss the implications of our results and how they can be tested observationally with current and forthcoming facilities (e.g., VLT, E-ELT, ALMA, and JWST) and with next-generation X-ray imaging satellites. By extrapolating the observed X-ray nebulae around local AGN to the environments of supermassive black holes at high redshifts, we find ≲1″ nebulae impose stringent design constraints on the spatial resolution of any future X-ray imaging Great Observatory in the coming decades.

Low Star Formation Activity and Low Gas Content of Quiescent Galaxies at z = 3.5–4.0 Constrained with ALMA

The discovery in deep near-infrared surveys of a population of massive quiescent galaxies at z > 3 has given rise to the question of how they came to be quenched so early in the history of the universe. Measuring their molecular gas properties can distinguish between physical processes where they stop forming stars due to a lack of fuel versus those where the star formation efficiency is reduced and the gas is retained. We conducted Atacama Large Millimeter/submillimeter Array observations of four quiescent galaxies at z = 3.5–4.0 found by the Fourstar Galaxy Evolution Survey and a serendipitous optically dark galaxy at z = 3.71. We aim to investigate the presence of dust-obscured star formation and their gas content by observing the dust continuum emission at Band 7 and the atomic carbon [C i](3 P 1–3 P 0) line at 492.16 GHz. Among the four quiescent galaxies, only one source is detected in the dust continuum at λ obs = 870 μm. The submillimeter observations confirm their passive nature, and all of them are located more than four times below the main sequence of star-forming galaxies at z = 3.7. None of the targets are detected in [C i], constraining their gas-mass fractions to be <20%. These gas-mass fractions are more than 3 times lower than the scaling relation for star-forming galaxies at z = 3.7. These results support scenarios where massive galaxies at z = 3.5–4.0 quench by consuming/expelling all the gas rather than by reducing the efficiency of the conversion of their gas into stars.

Massive star-forming galaxies have converted most of their halo gas into stars

In the local Universe, the efficiency for converting baryonic gas into stars is very low. In dark matter halos where galaxies form and evolve, the average efficiency varies with galaxy stellar mass and has a maximum of about 20% for Milky-Way-like galaxies. The low efficiency at higher mass is believed to be the result of some quenching processes, such as the feedback from active galactic nuclei. We perform an analysis of weak lensing and satellite kinematics for SDSS central galaxies. Our results reveal that the efficiency is much higher, more than 60%, for a large population of massive star-forming galaxies around 1011 M⊙. This suggests that these galaxies acquired most of the gas in their halos and converted it into stars without being significantly affected by quenching processes. This population of galaxies is not reproduced in current galaxy formation models, indicating that our understanding of galaxy formation is incomplete. The implications of our results on circumgalactic media, star-formation quenching, and disk galaxy rotation curves are discussed. We also examine systematic uncertainties in halo-mass and stellar-mass measurements that might influence our results.

A Search for Massive Galaxy Population in a Protocluster of LAEs at z = 2.39 near the Radio Galaxy 53W002

We searched for massive galaxy population in the known large-scale high-density structure of Lyα emitters (LAEs) at z = 2.39 near the radio galaxy 53W002 by using imaging data from bands taken with Suprime-Cam and MOIRCS on the Subaru telescope. We selected 62 protocluster member candidates by their JHK s -band colors and spectral energy distribution (SED) fitting analysis (JHK s -selected galaxies) in our survey field of and compared their physical properties estimated from the SED fitting with a comparison sample in the COSMOS field. We found significant number density excesses for the JHK s -selected galaxies in the 53W002 field at K s < 22.25, J − K s > 2, or V − K s > 4. In particular, the number density of the JHK s -selected galaxies with K s < 22.25 and J − K s > 2 in the 53W002 field is nine times higher than the comparison sample. Most of those with K s < 22.25 and J − K s > 2 are massive galaxies with M s > 1011 M ⊙, and their specific star formation rates (sSFRs) of 10−11–10−10 yr−1 suggest that the star formation has not yet stopped completely. We also found a density excess of quiescent galaxies with M s = 5 × 1010 M ⊙ to 1011 M ⊙ and sSFR < 10−11 yr−1, as well as that of low-mass galaxies with M s = 109.75–1010 M ⊙ and various sSFRs. The massive galaxies with M s > 1011 M ⊙ are not located at the density peaks of LAEs but widely distributed along a similar direction to the structure of LAEs over ∼15–20 comoving Mpc. On the other hand, the quiescent galaxies with sSFR < 10−11 yr−1 clearly avoid the structure of LAEs. Our results suggest that massive galaxies also exist in this protocluster discovered by the moderate overdensity of LAEs and their star formation activities depend on location in the protocluster.

Quenching of Massive Disk Galaxies in the IllustrisTNG Simulation

Abstract A rare population of massive disk galaxies have been found to invade the red sequence dominated by early-type galaxies. The formation and origins of these red/quenched massive disk galaxies have recently gained great interest. The quenching mechanisms that are usually proposed, such as bar quenching and environment quenching, do not seem to be suitable for those bulgeless quenched disks in a low-density environment. In this paper, we use the TNG300 simulation to investigate the formation of massive quenched central disk galaxies. It is found that these galaxies contain less gas than their star-forming counterparts and harbor giant super massive black holes (SMBHs; above 108 M ⊙). By tracing their formation history, we found that quenched disk galaxies formed early and preserved disk morphology for cosmological timescales. They have experienced less than one major merger on average, and mini-mergers (mass ratio &lt;1/10) have mainly contributed to the growth of their SMBHs. In the IllustrisTNG simulation, the black hole feedback mode switches from thermal to kinetic feedback when the black hole mass is more massive than ∼108 M ⊙, which is more efficient to eject gas outside of the galaxy and to suppress further cooling of the hot gaseous halo. We conclude that the dominant quenching mechanism in massive red/quenched disk galaxies is kinetic active galactic nuclei feedback.

Ultraviolet to far infrared self-consistent analysis of the stellar populations of massive starburst galaxies at intermediate redshifts

ABSTRACT We study in detail the properties of the stellar populations of 111 massive [log (M⋆/M⊙) ≥ 10] dusty [far-infrared (FIR)-selected] starburst (SFR/SFRMS &amp;gt; 2) galaxies at 0.7 &amp;lt; z &amp;lt; 1.2. For that purpose, we use self-consistent methods that analyse the UV-to-FIR broad-band observations in terms of the stellar light and dust re-emission with energy-balance techniques. We find that the emission of our starburst galaxies can be interpreted as a recent star formation episode superimposed on a more evolved stellar population. On average, the burst age is ∼80 Myr and its attenuation ∼2.4 mag. Assuming our starburst galaxies at half their lifetimes, we infer a duration of the starburst phase of ∼160 Myr. The median stellar mass and star formation rate (SFR) are log (M⋆/M⊙) ∼ 10.6 and ∼220 M⊙yr−1. Assuming this SFR and the inferred duration of the starburst phase, the stellar mass added during this phase corresponds to ∼40 per cent the median stellar mass of our sample. The young-population age determines the position of our galaxies in the M⋆–SFR plane. Galaxies located at the largest distances of the MS present shorter young-population ages. The properties of the underlying stellar population cannot be constrained accurately with our broad-band data. We also discuss the impact of including the FIR data and energy-balance techniques in the analysis of the properties of the stellar populations in starburst galaxies.