66 research outputs found
Molecular gas content and high excitation of a massive main-sequence galaxy at z = 3
We present new CO (J = 5-4 and 7-6) and [C I] (3P2-3P1 and 3P1-3P0) emission line observations of the star-forming galaxy D49 at the massive end of the main sequence at z = 3. We incorporate previous CO (J = 3-2) and optical-to-millimetre continuum observations to fit its spectral energy distribution. Our results hint at high-J CO luminosities exceeding the expected location on the empirical correlations with the infrared luminosity. [CI] emission fully consistent with the literature trends is found. We do not retrieve any signatures of a bright active galactic nucleus that could boost the J = 5-4, 7-6 lines in either the infrared or X-ray bands, but warm photon-dominated regions, shocks, or turbulence could in principle do so. We suggest that mechanical heating could be a favourable mechanism able to enhance the gas emission at fixed infrared luminosity in D49 and other main-sequence star-forming galaxies at high redshift, but further investigation is necessary to confirm this explanation. We derive molecular gas masses from dust, CO, and [C I] that all agree within the uncertainties. Given its high star formation rate ~500 Mo yr-1 and stellar mass > 1011.5 Mo, the short depletion timescale of < 0.3 Gyr might indicate that D49 is experiencing its last growth spurt and will soon transit to quiescence.</p
Compact, bulge dominated structures of spectroscopically confirmed quiescent galaxies at z~3
We study structural properties of spectroscopically confirmed massive
quiescent galaxies at with one of the first sizeable samples of
such sources, made of ten galaxies at
in the COSMOS field whose redshifts and quiescence are
confirmed by HST grism spectroscopy. Although affected by a weak bias toward
younger stellar populations, this sample is deemed to be largely representative
of the majority of the most massive and thus intrinsically rarest quiescent
sources at this cosmic time. We rely on targeted HST/WFC3 observations and fit
S\'ersic profiles to the galaxy surface brightness distributions at angstrom restframe. We find typically high S\'ersic indices and axis
ratios (medians and , respectively) suggesting that, at
odds with some previous results, the first massive quiescent galaxies may
largely be already bulge-dominated systems. We measure compact galaxy sizes
with an average of kpc at ,
in good agreement with the extrapolation at the highest masses of previous
determinations of the stellar mass - size relation of quiescent galaxies, and
of its redshift evolution, from photometrically selected samples at lower and
similar redshifts. This work confirms the existence of a population of compact,
bulge dominated, massive, quiescent sources at , providing one of
the first statistical estimates of their structural properties, and further
constraining the early formation and evolution of the first quiescent galaxies.Comment: 19 pages, 10 figures. Accepted for publication in MNRA
Cosmic evolution of radio-excess active galactic nuclei in quiescent and star-forming galaxies across 0 < z < 4
Context. Radio-excess active galactic nuclei (radio-AGNs) are essential to our understanding of both the physics of black hole (BH) accretion and the interaction between BHs and host galaxies. Recent deep and wide radio continuum surveys have made it possible to study radio-AGNs down to lower luminosities and up to higher redshifts than previous studies, and are providing new insights into the abundance and physical origin of radio-AGNs.Aims. Here we focus on the cosmic evolution, physical properties, and AGN-host galaxy connections of radio-AGNs selected from a total sample of âŒ400 000 galaxies at 0â<âzâ<â4 in the GOODS-N and COSMOS fields.Methods. Combining the deep radio continuum data with multi-band, de-blended far-infrared, and submillimeter data, we were able to identify 983 radio-AGNs out of the entire galaxy sample through radio excess relative to the far-infraredâradio relation.Results. We studied the cosmic evolution of 1.4 GHz radio luminosity functions (RLFs) for both star-forming galaxies (SFGs) and radio-AGNs, which can be well described by a pure luminosity evolution of Lââââ(1â
+â
z)â0.34â
Ăâ
zâ
+â
3.57 and a pure density evolution of Ίââââ(1â
+â
z)â0.77â
Ăâ
zâ
+â
2.69, respectively. We derived the turnover luminosity, above which the number density of radio-AGNs surpasses that of SFGs. We show that this crossover luminosity increases with increasing redshifts, from 1022.9 W Hzâ1 at zââŒâ0 to 1025.2 W Hzâ1 at zââŒâ4. At the full redshift range of 0â<âzâ<â4, we further derive the probability (pradio) of SFGs and quiescent galaxies (QGs) hosting a radio-AGN, as a function of stellar mass (Mâ), radio luminosity (LR), and redshift (z), which yields pradioâ
ââ
(1+z)3.08â
Mâ1.06â
LRâ0.77 for SFGs, and pradioâ
ââ
(1+z)2.47â
Mâ1.41â
LRâ0.60 for QGs, respectively.Conclusions. The quantitative relation for the probabilities of galaxies hosting a radio-AGN indicates that radio-AGNs in QGs prefer to reside in more massive galaxies with higher LR than those in SFGs. The fraction of radio-AGN increases toward higher redshift in both SFGs and QGs, with a more rapid increase in SFGs
A massive quiescent galaxy in a group environment at
We report on the spectroscopic confirmation of a massive quiescent galaxy at
in the COSMOS field with Keck/MOSFIRE. The object was
first identified as a galaxy with suppressed star formation at
from the COSMOS2020 catalog. The follow-up
spectroscopy with MOSFIRE in the -band reveals a faint [OII] emission and
the Balmer break, indicative of evolved stellar populations. We perform the
spectral energy distribution fitting using both the photometry and spectrum to
infer physical properties. The obtained stellar mass is high () and the current star formation rate is more than 1 dex
below that of main-sequence galaxies at . Its star formation history
suggests that this galaxy experienced starburst at followed by a rapid
quenching phase. This is one of the youngest quiescent galaxies at and is
likely a galaxy in the process of being quenched. An unique aspect of the
galaxy is that it is in an extremely dense region; there are four massive
star-forming galaxies at located within 150 physical
kpc from the galaxy. Interestingly, three of them have strongly overlapping
virial radii with that of the central quiescent galaxy (), suggesting that the over-density region is likely the
highest redshift candidate of a dense group with a spectroscopically confirmed
quiescent galaxy at the center. The group provides us with an unique
opportunity to gain insights into the role of the group environment for
quenching at 4 - 5 corresponding to the formation epoch of massive
elliptical galaxies in the local Universe.Comment: 13 pages, 7 figures, 2 tables; submitted to Ap
A galaxy group candidate at z approximate to 3.7 in the COSMOS field
We report a galaxy group candidate HPC1001 at z approximate to 3.7 in the COSMOS field. This structure was selected as a high galaxy overdensity at z > 3 in the COSMOS2020 catalog. It contains ten candidate members, of which eight are assembled in a 10 '' x 10 '' area with the highest sky density among known protoclusters and groups at z > 3. Four out of ten sources were also detected at 1.2mm with Atacama Large Millimeter Array continuum observations. Photometric redshifts, measured by four independent methods, fall within a narrow range of 3.5 < z < 3.9 and with a weighted average of z = 3.65 +/- 0.07. The integrated far-IR-to-radio spectral energy distribution yields a total UV and IR star formation rate SFR approximate to 900 M-circle dot yr(-1). We also estimated a halo mass of similar to 10(13) M-circle dot for the structure, which at this redshift is consistent with potential cold gas inflow. Remarkably, the most massive member has a specific star formation rate and dust to stellar mass ratio of M-dust/M-* that are both significantly lower than that of star-forming galaxies at this redshift, suggesting that HPC1001 could be a z approximate to 3.7 galaxy group in maturing phase. If confirmed, this would be the earliest structure in maturing phase to date, and an ideal laboratory to study the formation of the earliest quiescent galaxies as well as cold gas accretion in dense environments.Non peer reviewe
Massive galaxy formation caught in action at z~5 with JWST
We report the discovery of a compact group of galaxies, CGG-z5, at z~5.2 in
the EGS field covered by the JWST/CEERS survey. CGG-z5 was selected as the
highest overdensity of galaxies at z>2 in recent JWST public surveys and it
consists of six candidate members lying within a projected area of
(1020~kpc). All group members are HST/F435W and
HST/F606W dropouts while securely detected in the JWST/NIRCam bands, yielding a
narrow range of robust photometric redshifts . The most massive
galaxy in the group has a stellar mass log, while
the rest are low-mass satellites (log). While
several group members were already detected in the HST and IRAC bands, the low
stellar masses and the compactness of the structure required the sensitivity
and resolution of JWST for its identification. To assess the nature and
evolutionary path of CGG-z5, we searched for similar compact structures in the
\textsc{Eagle} simulations and followed their evolution with time. We find that
all the identified structures merge into a single galaxy by z=3 and form a
massive galaxy (log) at z~1. This implies that CGG-z5
could be a "proto-massive galaxy" captured during a short-lived phase of
massive galaxy formation.Comment: A&A Letter in pres
Insight Into a Lensed -dark Galaxy and its Quiescent Companion at
Using the novel /NIRCam observations in the Abell 2744 field, we
present a first spatially resolved overview of an -dark galaxy,
spectroscopically confirmed at with magnification .
While being largely invisible at 1 m with NIRCam, except for sparse
clumpy sub-structures, the object is well-detected and resolved in the
long-wavelength bands with a spiral shape clearly visible in F277W. By
combining ancillary ALMA and data, we infer that this object is an
edge-on dusty spiral with an intrinsic stellar mass log
and a dust-obscured SFR~yr. A massive quiescent galaxy
(log) with tidal features lies 2\farcs{0} away
(9 kpc), at a consistent redshift as inferred by photometry,
indicating a potential major merger. The dusty spiral lies on the main-sequence
of star formation, and shows high dust attenuation in the optical (). In the far-infrared, its integrated dust SED is optically thick up to
m, further supporting the extremely dusty nature.
Spatially resolved analysis of the -dark galaxy reveals a largely uniform
area spanning 57 kpc, which spatially matches to
the ALMA 1 mm continuum emission. Accounting for the surface brightness dimming
and the depths of current surveys, unlensed analogs of the -dark
galaxy at would be only detectable in F356W and F444W in UNCOVER-like
survey, and become totally -dark at . This suggests that
detecting highly attenuated galaxies in the Epoch of Reionization might be a
challenging task for .Comment: 15 pages, 5 figures, 1 table. Accepted to ApJ
"Super-deblended" dust emission in galaxies: II. Far-IR to (sub)millimeter photometry and high redshift galaxy candidates in the full COSMOS field
We present a "super-deblended" far-infrared to (sub)millimeter photometric catalog in the Cosmic Evolution Survey (COSMOS), prepared with the method recently developed by Liu et al. 2018, with key adaptations. We obtain point spread function (PSF) fitting photometry at fixed prior positions including 88,008 galaxies detected in either VLA 1.4~GHz, 3~GHz and/or MIPS 24~ÎŒm images. By adding a specifically carved mass-selected sample (with an evolving stellar mass limit), a highly complete prior sample of 194,428 galaxies is achieved for deblending FIR/(sub)mm images. We performed ``active' removal of non relevant priors at FIR/(sub)mm bands using spectral energy distribution (SED) fitting and redshift information. In order to cope with the shallower COSMOS data we subtract from the maps the flux of faint non-fitted priors and explicitly account for the uncertainty of this step. The resulting photometry (including data from Spitzer, Herschel, SCUBA2, AzTEC, MAMBO and NSF's Karl G. Jansky Very Large Array at 3~GHz and 1.4~GHz) displays well behaved quasi-Gaussian uncertainties, calibrated from Monte Carlo simulations and tailored to observables (crowding, residual maps). Comparison to ALMA photometry for hundreds of sources provide a remarkable validation of the technique. We detect 11,220 galaxies over the 100--1200~ÎŒm range, extending to zphotâŒ7. We conservatively selected a sample of 85 z>4 high redshift candidates, significantly detected in the FIR/(sub)mm, often with secure radio and/or Spitzer/IRAC counterparts. This provides a chance to investigate the first generation of vigorous starburst galaxies (SFRsâŒ1000Mâ~yrâ1). The photometric and value added catalogs are publicly released
Cosmic Vine: A z=3.44 Large-Scale Structure Hosting Massive Quiescent Galaxies
We report the discovery of a large-scale structure at z=3.44 revealed by JWST
data in the EGS field. This structure, dubbed "Cosmic Vine", consists of 20
galaxies with spectroscopic redshifts at and six galaxy
overdensities with consistent photometric redshifts, making up a vine-like
structure extending over a ~4x0.2 pMpc^2 area. The two most massive galaxies
(M*~10^10.9 Msun) of the Cosmic Vine are found to be quiescent with
bulge-dominated morphologies (). Comparisons with simulations suggest
that the Cosmic Vine would form a cluster with halo mass >10^14 Msun at z=0,
and the two massive galaxies are likely forming the brightest cluster galaxies
(BCGs). The results unambiguously reveal that massive quiescent galaxies can
form in growing large-scale structures at z>3, thus disfavoring the
environmental quenching mechanisms that require a virialized cluster core.
Instead, as suggested by the interacting and bulge-dominated morphologies, the
two galaxies are likely quenched by merger-triggered starburst or AGN feedback
before falling into a cluster core. Moreover, we found that the observed
specific star formation rates of massive quiescent galaxies in z>3 dense
environments are two orders of magnitude lower than that of the BCGs in the
TNG300 simulation. This discrepancy potentially poses a challenge to the models
of massive cluster galaxy formation. Future studies comparing a large sample
with dedicated cluster simulations are required to solve the problem.Comment: Submitted to A&
DEIMOS spectroscopy of protocluster candidate in COSMOS -- A massive protocluster embedded in a large scale structure?
We present the results of our Keck/DEIMOS spectroscopic follow-up of
candidate galaxies of i-band-dropout protocluster candidate galaxies at
in the COSMOS field. We securely detect Lyman- emission lines
in 14 of the 30 objects targeted, 10 of them being at with a
signal-to-noise ratio of , the remaining galaxies are either
non-detections or interlopers with redshift too different from to be part
of the protocluster. The 10 galaxies at make the protocluster one
of the riches at . The emission lines exhibit asymmetric profiles with
high skewness values ranging from 2.87 to 31.75, with a median of 7.37. This
asymmetry is consistent with them being Ly, resulting in a redshift
range of . Using the spectroscopic redshifts, we re-calculate the
overdensity map for the COSMOS field and find the galaxies to be in a
significant overdensity at the level, with a peak overdensity of
(compared to the previous value of ). The
protocluster galaxies have stellar masses derived from Bagpipes SED fits of
and star formation rates of
, placing them on the main sequence at
this epoch. Using a stellar-to-halo-mass relationship, we estimate the dark
matter halo mass of the most massive halo in the protocluster to be . By comparison with halo mass evolution tracks from
simulations, the protocluster is expected to evolve into a Virgo- or Coma-like
cluster in the present day.Comment: 26 pages, 14 figues, 5 tables, main text is 16 pages, appendix is 10
pages, published in MNRA
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