We present new measurements of the cosmic cold molecular gas evolution out to redshift 6 based on systematic mining of the Atacama Large Millimeter/submillimeter Array (ALMA) public archive in the ...COSMOS deep field (A3COSMOS). Our A3COSMOS data set contains ∼700 galaxies (0.3 z 6) with high-confidence ALMA detections in the (sub)millimeter continuum and multiwavelength spectral energy distributions. Multiple gas mass calibration methods are compared, and biases in band conversions (from observed ALMA wavelength to rest-frame Rayleigh-Jeans tail continuum) have been tested. Combining our A3COSMOS sample with ∼1000 CO-observed galaxies at 0 z 4 (75% at z < 0.1), we parameterize galaxies' molecular gas depletion time ( ) and molecular gas to stellar mass ratio ( ) each as a function of the stellar mass ( ), offset from the star-forming main sequence ( ) and cosmic age (or redshift). Our proposed functional form provides a statistically better fit to current data (than functional forms in the literature) and implies a "downsizing" effect (i.e., more-massive galaxies evolve earlier than less-massive ones) and "mass quenching" (gas consumption slows down with cosmic time for massive galaxies but speeds up for low-mass ones). Adopting galaxy stellar mass functions and applying our function for gas mass calculation, we for the first time infer the cosmic cold molecular gas density evolution out to redshift 6 and find agreement with CO blind surveys as well as semianalytic modeling. These together provide a coherent picture of cold molecular gas, star formation rate, and stellar mass evolution in galaxies across cosmic time.
We examine the behaviour of the infrared-radio correlation (IRRC) over the range 0 <z ≲ 6 using new, highly sensitive 3 GHz observations with the Karl G. Jansky Very Large Array (VLA) and infrared ...data from the Herschel Space Observatory in the 2 deg2 COSMOS field. We distinguish between objects where emission is believed to arise solely from star-formation, and those where an active galactic nucleus (AGN) is thought to be present. We account for non-detections in the radio or in the infrared using a doubly-censored survival analysis. We find that the IRRC of star-forming galaxies, quantified by the infrared-to-1.4 GHz radio luminosity ratio (qTIR), decreases with increasing redshift: qTIR(z) = (2.88 ± 0.03)(1 + z)− 0.19 ± 0.01. This is consistent with several previous results from the literature. Moderate-to-high radiative luminosity AGN do not follow the same qTIR(z) trend as star-forming galaxies, having a lower normalisation and steeper decrease with redshift. We cannot rule out the possibility that unidentified AGN contributions only to the radio regime may be steepening the observed qTIR(z) trend of the star-forming galaxy population. We demonstrate that the choice of the average radio spectral index directly affects the normalisation, as well as the derived trend with redshift of the IRRC. An increasing fractional contribution to the observed 3 GHz flux by free-free emission of star-forming galaxies may also affect the derived evolution. However, we find that the standard (M82-based) assumption of the typical radio spectral energy distribution (SED) for star-forming galaxies is inconsistent with our results. This suggests a more complex shape of the typical radio SED for star-forming galaxies, and that imperfect K corrections in the radio may govern the derived trend of decreasing qTIR with increasing redshift. A more detailed understanding of the radio spectrum is therefore required for robust K corrections in the radio and to fully understand the cosmic evolution of the IRRC. Lastly, we present a redshift-dependent relation between rest-frame 1.4 GHz radio luminosity and star formation rate taking the derived redshift trend into account.
Submillimeter/millimeter observations of dusty star-forming galaxies with the Atacama Large Millimeter/submillimeter Array (ALMA) have shown that dust continuum emission generally occurs in compact ...regions smaller than the stellar distribution. However, it remains to be understood how systematic these findings are. Studies often lack homogeneity in the sample selection, target discontinuous areas with inhomogeneous sensitivities, and suffer from modest
u
v
coverage coming from single array configurations. GOODS-ALMA is a 1.1 mm galaxy survey over a continuous area of 72.42 arcmin
2
at a homogeneous sensitivity. In this version 2.0, we present a new low resolution dataset and its combination with the previous high resolution dataset from the survey, improving the
u
v
coverage and sensitivity reaching an average of
σ
= 68.4 μJy beam
−1
. A total of 88 galaxies are detected in a blind search (compared to 35 in the high resolution dataset alone), 50% at
S
/
N
peak
≥ 5 and 50% at 3.5 ≤
S
/
N
peak
≤ 5 aided by priors. Among them, 13 out of the 88 are optically dark or faint sources (
H
- or
K
-band dropouts). The sample dust continuum sizes at 1.1 mm are generally compact, with a median effective radius of
R
e
= 0
.
″
10 ± 0
.
″
05 (a physical size of
R
e
= 0.73 ± 0.29 kpc at the redshift of each source). Dust continuum sizes evolve with redshift and stellar mass resembling the trends of the stellar sizes measured at optical wavelengths, albeit a lower normalization compared to those of late-type galaxies. We conclude that for sources with flux densities
S
1.1 mm
> 1 mJy, compact dust continuum emission at 1.1 mm prevails, and sizes as extended as typical star-forming stellar disks are rare. The
S
1.1 mm
< 1 mJy sources appear slightly more extended at 1.1 mm, although they are still generally compact below the sizes of typical star-forming stellar disks.
ABSTRACT
We present an analysis of the dust attenuation of star-forming galaxies at z = 2.5–4.0 through the relationship between the UV spectral slope (β), stellar mass (M*), and the infrared excess ...(IRX = LIR/LUV) based on far-infrared continuum observations from the Atacama Large Millimeter/sub-millimeter Array (ALMA). Our study exploits the full ALMA archive over the COSMOS field processed by the A3COSMOS team, which includes an unprecedented sample of ∼1500 galaxies at z ∼ 3 as primary or secondary targets in ALMA band 6 or 7 observations with a median continuum sensitivity of 126 $\rm {\mu Jy\, beam}^{-1}$ (1σ). The detection rate is highly mass dependent, decreasing drastically below log (M*/M⊙) = 10.5. The detected galaxies show that the IRX–β relationship of massive (log M*/M⊙ > 10) main-sequence galaxies at z = 2.5–4.0 is consistent with that of local galaxies, while starbursts are generally offset by $\sim 0.5\, {\rm dex}$ to larger IRX values. At the low-mass end, we derive upper limits on the infrared luminosities through stacking of the ALMA data. The combined IRX–M* relation at $\rm {log\, ({\it M}_{\ast }/\mathrm{M}_{\odot })\gt 9}$ exhibits a significantly steeper slope than reported in previous studies at similar redshifts, implying little dust obscuration at log M*/M⊙ < 10. However, our results are consistent with earlier measurements at z ∼ 5.5, indicating a potential redshift evolution between z ∼ 2 and z ∼ 6. Deeper observations targeting low-mass galaxies will be required to confirm this finding.
We study the incidence of nuclear obscuration on a complete sample of 1310 active galactic nuclei (AGN) selected on the basis of their rest-frame 2-10 keV X-ray flux from the XMM-COSMOS survey, in ...the redshift range 0.3 < z < 3.5. We classify the AGN as obscured or unobscured on the basis of either the optical spectral properties and the overall SED or the shape of the X-ray spectrum. The two classifications agree in about 70 per cent of the objects, and the remaining 30 per cent can be further subdivided into two distinct classes: at low luminosities X-ray unobscured AGN do not always show signs of broad lines or blue/UV continuum emission in their optical spectra, most likely due to galaxy dilution effects; at high-luminosities broad-line AGN may have absorbed X-ray spectra, which hints at an increased incidence of small-scale (sub-parsec) dust-free obscuration. We confirm that the fraction of obscured AGN is a decreasing function of the intrinsic X-ray luminosity, while the incidence of absorption shows significant evolution only for the most luminous AGN, which appear to be more commonly obscured at higher redshift. We find no significant difference between the mean stellar masses and star formation rates of obscured and unobscured AGN hosts. We conclude that the physical state of the medium responsible for obscuration in AGN is complex and mainly determined by the radiation environment (nuclear luminosity) in a small region enclosed within the gravitational sphere of influence of the central black hole, but is largely insensitive to the wider scale galactic conditions.
Abstract
We present results on the dust attenuation of galaxies at redshift ∼3–6 by studying the relationship between the UV spectral slope (βUV) and the infrared excess (IRX; L
IR/L
UV) using ...Atacama Large Millimeter/submillimeter Array (ALMA) far-infrared continuum observations. Our study is based on a sample of 67 massive, star-forming galaxies with a median mass of M
* ∼ 1010.7 M
⊙ spanning a redshift range z = 2.6–3.7 (median z = 3.2) that were observed with ALMA at
$\lambda _{\text{rest}}=300\,{\rm \mu m}$
. Both the individual ALMA detections (41 sources) and stacks including all galaxies show the IRX–βUV relationship at z ∼ 3 is mostly consistent with that of local starburst galaxies on average. However, we find evidence for a large dispersion around the mean relationship by up to ±0.5 dex. Nevertheless, the locally calibrated dust correction factors based on the IRX–βUV relation are on average applicable to main-sequence z ∼ 3 galaxies. This does not appear to be the case at even higher redshifts, however. Using public ALMA observations of z ∼ 4–6 galaxies we find evidence for a significant evolution in the IRX–βUV and the IRX–M
* relations beyond z ∼ 3 towards lower IRX values. We discuss several caveats that could affect these results, including the assumed dust temperature. ALMA observations of larger z > 3 galaxy sample spanning a wide range of physical parameters (e.g. lower stellar mass) will be important to investigate this intriguing redshift evolution further.
ABSTRACT We present an analysis of a deep (1 = 13 Jy) cosmological 1.2 mm continuum map based on ASPECS, the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field. In the 1 arcmin2 covered by ...ASPECS we detect nine sources at significance at 1.2 mm. Our ALMA-selected sample has a median redshift of , with only one galaxy detected at z > 2 within the survey area. This value is significantly lower than that found in millimeter samples selected at a higher flux density cutoff and similar frequencies. Most galaxies have specific star formation rates (SFRs) similar to that of main-sequence galaxies at the same epoch, and we find median values of stellar mass and SFRs of and yr−1, respectively. Using the dust emission as a tracer for the interstellar medium (ISM) mass, we derive depletion times that are typically longer than 300 Myr, and we find molecular gas fractions ranging from ∼0.1 to 1.0. As noted by previous studies, these values are lower than those using CO-based ISM estimates by a factor of ∼2. The 1 mm number counts (corrected for fidelity and completeness) are in agreement with previous studies that were typically restricted to brighter sources. With our individual detections only, we recover 55% 4% of the extragalactic background light (EBL) at 1.2 mm measured by the Planck satellite, and we recover 80% 7% of this EBL if we include the bright end of the number counts and additional detections from stacking. The stacked contribution is dominated by galaxies at , with stellar masses of (1-3) × 1010 M . For the first time, we are able to characterize the population of galaxies that dominate the EBL at 1.2 mm.
We present an analysis of the deepest Herschel images in four major extragalactic fields GOODS–North, GOODS–South, UDS, and COSMOS obtained within the GOODS–Herschel and CANDELS–Herschel key ...programs. The star formation picture provided by a total of 10 497 individual far-infrared detections is supplemented by the stacking analysis of a mass complete sample of 62 361 star-forming galaxies from the Hubble Space Telescope (HST) H band-selected catalogs of the CANDELS survey and from two deep ground-based Ks band-selected catalogs in the GOODS–North and the COSMOS-wide field to obtain one of the most accurate and unbiased understanding to date of the stellar mass growth over the cosmic history. We show, for the first time, that stacking also provides a powerful tool to determine the dispersion of a physical correlation and describe our method called “scatter stacking”, which may be easily generalized to other experiments. The combination of direct UV and far-infrared UV-reprocessed light provides a complete census on the star formation rates (SFRs), allowing us to demonstrate that galaxies at z = 4 to 0 of all stellar masses (M∗) follow a universal scaling law, the so-called main sequence of star-forming galaxies. We find a universal close-to-linear slope of the log 10(SFR)–log 10(M∗) relation, with evidence for a flattening of the main sequence at high masses (log 10(M∗/M⊙) > 10.5) that becomesless prominent with increasing redshift and almost vanishes by z ≃ 2. This flattening may be due to the parallel stellar growth of quiescent bulges in star-forming galaxies, which mostly happens over the same redshift range. Within the main sequence, we measure a nonvarying SFR dispersion of 0.3 dex: at a fixed redshift and stellar mass, about 68% of star-forming galaxies form stars at a universal rate within a factor 2. The specific SFR (sSFR = SFR/M∗) of star-forming galaxies is found to continuously increase from z = 0 to 4. Finally we discuss the implications of our findings on the cosmic SFR history and on the origin of present-day stars: more than two-thirds of present-day stars must have formed in a regime dominated by the “main sequence” mode. As a consequence we conclude that, although omnipresent in the distant Universe, galaxy mergers had little impact in shaping the global star formation history over the last 12.5 billion years.
Massive starburst galaxies in the early Universe are estimated to have depletion times of ∼100 Myr and thus be able to convert their gas very quickly into stars, possibly leading to a rapid quenching ...of their star formation. For these reasons, they are considered progenitors of massive early-type galaxies (ETGs). In this paper, we study two high-
z
starbursts, AzTEC/C159 (
z
≃ 4.57) and J1000+0234 (
z
≃ 4.54), observed with ALMA in the C
II
158-
μ
m emission line. These observations reveal two massive and regularly rotating gaseous discs. A 3D modelling of these discs returns rotation velocities of about 500 km s
−1
and gas velocity dispersions as low as ≈ 20 km s
−1
, leading to very high ratios between regular and random motion (
V
/
σ
≳ 20), at least in AzTEC/C159. The mass decompositions of the rotation curves show that both galaxies are highly baryon-dominated with gas masses of ≈10
11
M
⊙
, which, for J1000+0234, is significantly higher than previous estimates. We show that these high-
z
galaxies overlap with
z
= 0 massive ETGs in the ETG analogue of the stellar-mass Tully-Fisher relation once their gas is converted into stars. This provides dynamical evidence of the connection between massive high-
z
starbursts and ETGs, although the transformation mechanism from fast rotating to nearly pressure-supported systems remains unclear.
The emergence of passive galaxies in the early Universe results from the delicate interplay among the different physical processes responsible for their rapid assembly and the abrupt shut-down of ...their star formation activity. Investigating the individual properties and demographics of early passive galaxies improves our understanding of these mechanisms. In this work we present a follow-up analysis of the
z
> 3 passive galaxy candidates selected by Merlin et al. (2019, MNRAS, 490, 3309) in the CANDELS fields. We begin by first confirming the accuracy of their passive classification by exploiting their sub-millimetre emission to demonstrate the lack of ongoing star formation. Using archival ALMA observations we are able to confirm at least 61% of the observed candidates as passive. While the remainder lack sufficiently deep data for confirmation, we are able to validate the entire sample in a statistical sense. We then estimate the stellar mass function (SMF) of all 101 passive candidates in three redshift bins from
z
= 5 to
z
= 3. We adopt a stepwise approach that has the advantage of taking into account photometric errors, mass and selection completeness issues, as well as the Eddington bias, without any a posteriori correction. We observe a pronounced evolution in the SMF around
z
∼ 4, indicating that we are witnessing the emergence of the passive population at this epoch. Massive (
M
> 10
11
M
⊙
) passive galaxies, only accounting for a small (< 10%) fraction of galaxies at
z
> 4, become dominant at later epochs. Thanks to a combination of photometric quality, sample selection, and methodology, we overall find a higher density of passive galaxies than in previous works. The comparison with theoretical predictions, despite a qualitative agreement (at least for some of the models considered), denotes a still incomplete understanding of the physical processes responsible for the formation of these galaxies. Finally, we extrapolate our results to predict the number of early passive galaxies expected in surveys carried out with future facilities.
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