We report the serendipitous detection of two 3 mm continuum sources found in deep ALMA Band 3 observations to study intermediate-redshift galaxies in the COSMOS field. One is near a foreground galaxy ...at 1 3, but is a previously unknown dust-obscured star-forming galaxy (DSFG) at probable zCO = 3.329, illustrating the risk of misidentifying shorter wavelength counterparts. The optical-to-millimeter spectral energy distribution (SED) favors a gray λ−0.4 attenuation curve and results in significantly larger stellar mass and SFR compared to a Calzetti starburst law, suggesting caution when relating progenitors and descendants based on these quantities. The other source is missing from all previous optical/near-infrared/submillimeter/radio catalogs ("ALMA-only"), and remains undetected even in stacked ultradeep optical (>29.6 AB) and near-infrared (>27.9 AB) images. Using the ALMA position as a prior reveals faint signal-to-noise ratio ∼ 3 measurements in stacked IRAC 3.6+4.5, ultradeep SCUBA2 850 m, and VLA 3 GHz, indicating the source is real. The SED is robustly reproduced by a massive M* = 1010.8M and Mgas = 1011M , highly obscured AV ∼ 4, star-forming SFR ∼ 300 M yr−1 galaxy at redshift z = 5.5 1.1. The ultrasmall 8 arcmin2 survey area implies a large yet uncertain contribution to the cosmic star formation rate density CSFRD(z = 5) ∼ 0.9 × 10−2 M yr−1 Mpc−3, comparable to all ultraviolet-selected galaxies combined. These results indicate the existence of a prominent population of DSFGs at z > 4, below the typical detection limit of bright galaxies found in single-dish submillimeter surveys, but with larger space densities ∼3 × 10−5 Mpc−3, higher duty cycles of 50%-100%, contributing more to the CSFRD, and potentially dominating the high-mass galaxy stellar mass function.
Abstract
The first few 100 Myr at
z
> 10 mark the last major uncharted epoch in the history of the universe, where only a single galaxy (GN-z11 at
z
≈ 11) is currently spectroscopically confirmed. ...Here we present a search for luminous
z
> 10 galaxies with JWST/NIRCam photometry spanning ≈1–5
μ
m and covering 49 arcmin
2
from the public JWST Early Release Science programs (CEERS and GLASS). Our most secure candidates are two
M
UV
≈ −21 systems: GLASS-z12 and GLASS-z10. These galaxies display abrupt ≳1.8 mag breaks in their spectral energy distributions (SEDs), consistent with complete absorption of flux bluewards of Ly
α
that is redshifted to
z
=
12.4
−
0.3
+
0.1
and
z
=
10.4
−
0.5
+
0.4
. Lower redshift interlopers such as quiescent galaxies with strong Balmer breaks would be comfortably detected at >5
σ
in multiple bands where instead we find no flux. From SED modeling we infer that these galaxies have already built up ∼10
9
solar masses in stars over the ≲300–400 Myr after the Big Bang. The brightness of these sources enable morphological constraints. Tantalizingly, GLASS-z10 shows a clearly extended exponential light profile, potentially consistent with a disk galaxy of
r
50
≈ 0.7 kpc. These sources, if confirmed, join GN-z11 in defying number density forecasts for luminous galaxies based on Schechter UV luminosity functions, which require a survey area >10× larger than we have studied here to find such luminous sources at such high redshifts. They extend evidence from lower redshifts for little or no evolution in the bright end of the UV luminosity function into the cosmic dawn epoch, with implications for just how early these galaxies began forming. This, in turn, suggests that future deep JWST observations may identify relatively bright galaxies to much earlier epochs than might have been anticipated.
Abstract
Collisions and interactions between gas-rich galaxies are thought to be pivotal stages in their formation and evolution, causing the rapid production of new stars, and possibly serving as a ...mechanism for fueling supermassive black holes (BHs). Harnessing the exquisite spatial resolution (∼0${^{\prime\prime}_{.}}$5) afforded by the first ∼170 deg2 of the Hyper Suprime-Cam (HSC) survey, we present our new constraints on the importance of galaxy–galaxy major mergers (1 : 4) in growing BHs throughout the last ∼8 Gyr. Utilizing mid-infrared observations in the WISE all-sky survey, we robustly select active galactic nuclei (AGN) and mass-matched control galaxy samples, totaling ∼140000 spectroscopically confirmed systems at i < 22 mag. We identify galaxy interaction signatures using a novel machine-learning random forest decision tree technique allowing us to select statistically significant samples of major mergers, minor mergers / irregular systems, and non-interacting galaxies. We use these samples to show that galaxies undergoing mergers are a factor of ∼2–7 more likely to contain luminous obscured AGN than non-interacting galaxies, and this is independent of both stellar mass and redshift to z < 0.9. Furthermore, based on our comparison of AGN fractions in mass-matched samples, we determine that the most luminous AGN population (LAGN ≳ 1045 erg s−1) systematically reside in merging systems over non-interacting galaxies. Our findings show that galaxy–galaxy interactions do, on average, trigger luminous AGN activity substantially more often than in secularly evolving non-interacting galaxies, and we further suggest that the BH growth rate may be closely tied to the dynamical time of the merger system.
Abstract
We present Atacama Large Millimeter/submillimeter Array (ALMA) CO(2–1) spectroscopy of six massive (log
10
/
> 11.3) quiescent galaxies at
z
∼ 1.5. These data represent the largest sample ...using CO emission to trace molecular gas in quiescent galaxies above
z
> 1, achieving an average 3
σ
sensitivity of
∼ 10
10
. We detect one galaxy at 4
σ
significance and place upper limits on the molecular gas reservoirs of the other five, finding molecular gas mass fractions
(3
σ
upper limits). This is 1–2 orders of magnitude lower than coeval star-forming galaxies at similar stellar mass, and comparable to galaxies at
z
= 0 with similarly low specific star formation rate (sSFR). This indicates that their molecular gas reservoirs were rapidly and efficiently used up or destroyed, and that gas fractions are uniformly low (<6%) despite the structural diversity of our sample. The implied rapid depletion time of molecular gas (
< 0.6 Gyr) disagrees with extrapolations of empirical scaling relations to low sSFR. We find that our low gas fractions are instead in agreement with predictions from both the recent
simba
cosmological simulation, and from analytical “bathtub” models for gas accretion onto galaxies in massive dark matter halos (log
at
z
= 0). Such high mass halos reach a critical mass of log
by
z
∼ 4 that halt the accretion of baryons early in the universe. Our data are consistent with a simple picture where galaxies truncate accretion and then consume the existing gas at or faster than typical main-sequence rates. Alternatively, we cannot rule out that these galaxies reside in lower mass halos, and low gas fractions may instead reflect either stronger feedback, or more efficient gas consumption.
Abstract
We use CEERS JWST/NIRCam imaging to measure rest-frame near-IR light profiles of 435
M
⋆
> 10
10
M
⊙
galaxies in the redshift range of 0.5 <
z
< 2.3. We compare the resulting rest-frame ...1.5–2
μ
m half-light radii (
R
NIR
) with stellar half-mass radii (
R
M
⋆
) derived with multicolor light profiles from CANDELS Hubble Space Telescope imaging. In general agreement with previous work, we find that
R
NIR
and
R
M
⋆
are up to 40% smaller than the rest-frame optical half-light radius
R
opt
. The agreement between
R
NIR
and
R
M
⋆
is excellent, with a negligible systematic offset (<0.03 dex) up to
z
= 2 for quiescent galaxies and up to
z
= 1.5 for star-forming galaxies. We also deproject the profiles to estimate
R
M
⋆
,
3
D
, the radius of a sphere containing 50% of the stellar mass. We present the
R
−
M
⋆
distribution of galaxies at 0.5 <
z
< 1.5, comparing
R
opt
,
R
M
⋆
, and
R
M
⋆
,
3
D
. The slope is significantly flatter for
R
M
⋆
and
R
M
⋆
,
3
D
compared to
R
opt
, mostly due to downward shifts in size for massive star-forming galaxies, while
R
M
⋆
and
R
M
⋆
,
3
D
do not show markedly different trends. Finally, we show rapid evolution of the size (
R
∝ (1 +
z
)
−1.7±0.1
) of massive (
M
⋆
> 10
11
M
⊙
) quiescent galaxies between
z
= 0.5 and
z
= 2.3, again comparing
R
opt
,
R
M
⋆
, and
R
M
⋆
,
3
D
. We conclude that the main tenets of the evolution of the size narrative established over the past 20 yr, based on rest-frame optical light profile analysis, still hold in the era of JWST/NIRCam observations in the rest-frame near-IR.
One of the greatest challenges to theoretical models of massive galaxy formation is the regulation of star formation at early times. The relative roles of molecular gas expulsion, depletion, and ...stabilization are uncertain as direct observational constraints of the gas reservoirs in quenched or quenching galaxies at high redshift are scant. We present ALMA observations of CO(2-1) in a massive ( ), recently quenched galaxy at z = 1.522. The optical spectrum of this object shows strong Balmer absorption lines, which implies that star formation ceased ∼0.8 Gyr ago. We do not detect CO(2-1) line emission, placing an upper limit on the molecular gas mass of . The implied gas fraction is , lower than typical star-forming galaxies at similar stellar masses at this redshift, among the lowest gas fractions at this specific star formation rate at any epoch, and the most stringent constraint on the gas contents of a passive galaxy to date. Our observations show that the depletion of from the interstellar medium of quenched objects can be both efficient and fairly complete, in contrast to recent claims of significant cold gas in recently quenched galaxies. We explore the variation in observed gas fractions in high-z galaxies and show that galaxies with high stellar surface density have low , similar to recent correlations between specific star formation rate and stellar surface density.
In this paper, we investigate the relationship between star formation and structure, using a mass-complete sample of 27,893 galaxies at 0.5 < z < 2.5 selected from 3D-HST. We confirm that ...star-forming galaxies are larger than quiescent galaxies at fixed stellar mass ( ). However, in contrast with some simulations, there is only a weak relation between star formation rate (SFR) and size within the star-forming population: when dividing into quartiles based on residual offsets in SFR, we find that the sizes of star-forming galaxies in the lowest quartile are 0.27 0.06 dex smaller than the highest quartile. We show that 50% of star formation in galaxies at fixed takes place within a narrow range of sizes (0.26 dex). Taken together, these results suggest that there is an abrupt cessation of star formation after galaxies attain particular structural properties. Confirming earlier results, we find that central stellar density within a 1 kpc fixed physical radius is the key parameter connecting galaxy morphology and star formation histories: galaxies with high central densities are red and have increasingly lower SFR/ , whereas galaxies with low central densities are blue and have a roughly constant (higher) SFR/ at a given redshift. We find remarkably little scatter in the average trends and a strong evolution of >0.5 dex in the central density threshold correlated with quiescence from z ∼ 0.7-2.0. Neither a compact size nor high-n are sufficient to assess the likelihood of quiescence for the average galaxy; instead, the combination of these two parameters together with results in a unique quenching threshold in central density/velocity.
We present high spatial resolution imaging of the CO(1-0) line from the Karl G. Jansky Very Large Array of COSMOS 27289, a massive, compact star-forming galaxy (SFG) at z = 2.234. This galaxy was ...selected because of its structural similarity to z ∼ 2 passive galaxies. Our previous observations showed that it is very gas poor with respect to typical SFGs at these redshifts, consistent with a rapid transition to quiescence as the molecular gas is depleted. The new data show that both the molecular gas fraction, , and the molecular gas depletion time, /SFR, are lower in the central 1-2 kpc of the galaxy and rise at larger radii ∼2-4 kpc. These observations are consistent with a scenario in which COSMOS 27289 will imminently cease star formation in the inner regions before the outskirts, i.e., inside-out quenching, the first time this phenomenon has been seen via observations of molecular gas in the high-redshift universe. We find good qualitative and quantitative agreement with a hydrodynamical simulation of galaxy quenching, in which the central suppression of molecular gas arises due to rapid gas consumption and outflows that evacuate the central regions of gas. Our results provide independent evidence for inside-out quenching of star formation as a plausible formation mechanism for z ∼ 2 quiescent galaxies.
We report the detection of morphology-dependent stellar age in massive quenched galaxies (QGs) at z ∼ 1.2. The sense of the dependence is that compact QGs are 0.5-2 Gyr older than normal-sized ones. ...The evidence comes from three different age indicators- D n 4000 , H δ , and fits to spectral synthesis models-applied to their stacked optical spectra. All age indicators consistently show that the stellar populations of compact QGs are older than those of their normal-sized counterparts. We detect weak O ii emission in a fraction of QGs, and the strength of the line, when present, is similar between the two samples; however, compact galaxies exhibit a significantly lower frequency of O ii emission than normal ones. Fractions of both samples are individually detected in 7 Ms Chandra X-ray images (luminosities ∼1040-1041 erg s−1). The 7 Ms stacks of nondetected galaxies show similarly low luminosities in the soft band only, consistent with a hot gas origin for the X-ray emission. While both O ii emitters and nonemitters are also X-ray sources among normal galaxies, no compact galaxy with O ii emission is an X-ray source, arguing against an active galactic nucleus (AGN) powering the line in compact galaxies. We interpret the O ii properties as further evidence that compact galaxies are older and further along in the process of quenching star formation and suppressing gas accretion. Finally, we argue that the older age of compact QGs is evidence of progenitor bias: compact QGs simply reflect the smaller sizes of galaxies at their earlier quenching epoch, with stellar density most likely having nothing directly to do with cessation of star formation.
Star formation in half of massive galaxies was quenched by the time the Universe was 3 billion years old.sup.1. Very low amounts of molecular gas seem to be responsible for this, at least in some ...cases.sup.2-7, although morphological gas stabilization, shock heating or activity associated with accretion onto a central supermassive black hole are invoked in other cases.sup.8-11. Recent studies of quenching by gas depletion have been based on upper limits that are insufficiently sensitive to determine this robustly.sup.2-7, or stacked emission with its problems of averaging.sup.8,9. Here we report 1.3 mm observations of dust emission from 6 strongly lensed galaxies where star formation has been quenched, with magnifications of up to a factor of 30. Four of the six galaxies are undetected in dust emission, with an estimated upper limit on the dust mass of 0.0001 times the stellar mass, and by proxy (assuming a Milky Way molecular gas-to-dust ratio) 0.01 times the stellar mass in molecular gas. This is two orders of magnitude less molecular gas per unit stellar mass than seen in star forming galaxies at similar redshifts.sup.12-14. It remains difficult to extrapolate from these small samples, but these observations establish that gas depletion is responsible for a cessation of star formation in some fraction of high-redshift galaxies.
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