ABSTRACT
We study the interstellar medium (ISM) properties as a function of the molecular gas size for 77 infrared-selected galaxies at z ∼ 1.3, having stellar masses 109.4 ≲ M⋆ ≲ 1012.0 M⊙ and star ...formation rates 12 ≲ SFRFIR ≲ 1000 M⊙ yr−1. Molecular gas sizes are measured on ALMA images that combine CO(2-1), CO(5-4), and underlying continuum observations, and include CO(4-3), CO(7-6) + CI(3P2 − 3P1), CI(3P1 − 3P0) observations for a subset of the sample. The $\gtrsim $46 per cent of our galaxies have a compact molecular gas reservoir, and lie below the optical discs mass–size relation. Compact galaxies on and above the main sequence have higher CO excitation and star formation efficiency than galaxies with extended molecular gas reservoirs, as traced by CO(5-4)/CO(2-1) and CO(2-1)/LIR, SF ratios. Average CO + CI spectral line energy distributions indicate higher excitation in compacts relative to extended sources. Using CO(2-1) and dust masses as molecular gas mass tracers, and conversion factors tailored to their ISM conditions, we measure lower gas fractions in compact main-sequence galaxies compared to extended sources. We suggest that the submillimetre compactness, defined as the ratio between the molecular gas and the stellar size, is an unavoidable information to be used with the main sequence offset to describe the ISM properties of galaxies, at least above M⋆ ≥ 1010.6 M⊙, where our observations fully probe the main sequence scatter. Our results are consistent with mergers driving the gas in the nuclear regions, enhancing the CO excitation and star formation efficiency. Compact main-sequence galaxies are consistent with being an early post-starburst population following a merger-driven starburst episode, stressing the important role of mergers in the evolution of massive galaxies.
We report Atacama Large Millimeter Array observations of the neutral atomic carbon transitions C i and multiple CO lines in a sample of ∼30 main-sequence galaxies at , including novel information on ...C i and CO for 7 of such normal objects. We complement our observations with a collection of >200 galaxies with coverage of similar transitions, spanning the z = 0-4 redshift interval and a variety of ambient conditions from local to high-redshift starbursts. We find systematic variations in the C i/IR and C i/high-Jupper (Jupper = 7) CO luminosity ratios among the various samples. We interpret these differences as increased dense molecular gas fractions and star formation efficiencies in the strongest high-redshift starbursts with respect to normal main-sequence galaxies. We further report constant / ratios across the galaxy populations and redshifts, suggesting that gas temperatures Texc traced by C i do not strongly vary. We find only a mild correlation with Tdust and that, generally, Texc Tdust. We fit the line ratios with classical photodissociation region models, retrieving consistently larger densities and intensities of the UV radiation fields in submillimeter galaxies than in main-sequence and local objects. However, these simple models fall short in representing the complexity of a multiphase interstellar medium and should be treated with caution. Finally, we compare our observations with the Santa Cruz semi-analytical model of galaxy evolution, recently extended to simulate submillimeter emission. While we confirm the success in reproducing the CO lines, we find systematically larger C i luminosities at fixed IR luminosity than predicted theoretically. This highlights the necessity of improving our understanding of the mechanisms regulating the C i emission on galactic scales. We release our data compilation to the community.
We present the first results of an Atacama Large Millimeter Array survey of the lower fine-structure line of atomic carbon C i in far-infrared-selected galaxies on the main sequence at z ∼ 1.2 in the ...COSMOS field. We compare our sample with a comprehensive compilation of data available in the literature for local and high-redshift starbursting systems and quasars. We show that the C i (3P1 → 3P0) luminosity correlates on global scales with the infrared luminosity , similar to low-J CO transitions. We report a systematic variation of / as a function of the galaxy type, with the ratio being larger for main-sequence galaxies than for starbursts and submillimeter galaxies at fixed . The / and / mass ratios are similar for main-sequence galaxies and for local and high-redshift starbursts within a 0.2 dex intrinsic scatter, suggesting that C i is a good tracer of molecular gas mass as CO and dust. We derive a fraction of of the total carbon mass in the atomic neutral phase. Moreover, we estimate the neutral atomic carbon abundance, the fundamental ingredient to calibrate C i as a gas tracer, by comparing and available gas masses from CO lines and dust emission. We find lower C i abundances in main-sequence galaxies than in starbursting systems and submillimeter galaxies as a consequence of the canonical CO and gas-to-dust conversion factors. This argues against the application to different galaxy populations of a universal standard C i abundance derived from highly biased samples.
We present the first stellar velocity dispersion measurement of a massive quenching galaxy at z = 4. The galaxy is first identified as a massive z ≥ 4 galaxy with suppressed star formation from ...photometric redshifts based on deep multiband data. A follow-up spectroscopic observation with MOSFIRE on Keck revealed strong multiple absorption features, which are identified as Balmer lines, giving a secure redshift of z = 4.01. This is the most distant quiescent galaxy known to date. Thanks to the high S/N of the spectrum, we are able to estimate the stellar velocity dispersion, , making a significant leap from the previous highest redshift measurement at z = 2.8. Interestingly, we find that the velocity dispersion is consistent with that of massive galaxies today, implying no significant evolution in velocity dispersion over the last 12 Gyr. Based on a stringent upper limit on its physical size from deep optical images (reff < 1.3 kpc), we find that its dynamical mass is consistent with the stellar mass inferred from photometry. Furthermore, the galaxy is located on the mass fundamental plane extrapolated from lower redshift galaxies. The observed no strong evolution in suggests that the mass in the core of massive galaxies does not evolve significantly, while most of the mass growth occurs in the outskirts of the galaxies, which also increases the size. This picture is consistent with a two-phase formation scenario in which mass and size growth is due to accretion in the outskirts of galaxies via mergers. Our results imply that the first phase may be completed as early as z ∼ 4.
Abstract
We present the results of a systematic search for candidate quiescent galaxies in the distant universe in 11 JWST fields with publicly available observations collected during the first 3 ...months of operations and covering an effective sky area of ∼145 arcmin
2
. We homogeneously reduce the new JWST data and combine them with existing observations from the Hubble Space Telescope. We select a robust sample of ∼80 candidate quiescent and quenching galaxies at 3 <
z
< 5 using two methods: (1) based on their rest-frame
UVJ
colors, and (2) a novel quantitative approach based on Gaussian mixture modeling of the near-UV −
U
,
U
−
V
, and
V
−
J
rest-frame color space, which is more sensitive to recently quenched objects. We measure comoving number densities of massive (
M
⋆
≥ 10
10.6
M
⊙
) quiescent galaxies consistent with previous estimates relying on ground-based observations, after homogenizing the results in the literature with our mass and redshift intervals. However, we find significant field-to-field variations of the number densities up to a factor of 2–3, highlighting the effect of cosmic variance and suggesting the presence of overdensities of red quiescent galaxies at
z
> 3, as could be expected for highly clustered massive systems. Importantly, JWST enables the robust identification of quenching/quiescent galaxy candidates at lower masses and higher redshifts than before, challenging standard formation scenarios. All data products, including the literature compilation, are made publicly available.
Abstract
We present the first spatially resolved measurements of galaxy properties in the JWST ERO SMACS 0723 field. We perform a comprehensive analysis of five 5 <
z
< 9 galaxies with spectroscopic ...redshifts from NIRSpec observations. We perform spatially resolved spectral energy distribution fitting with
Bagpipes
, using six NIRCam imaging bands spanning the wavelength range 0.8–5
μ
m. This approach allows us to study the internal structure and assembly of the first generations of galaxies. We find clear gradients both in the empirical color maps and in most of the estimated physical parameters. We find regions of considerably different specific star formation rates across each galaxy, which points to very bursty star formation happening on small scales, not galaxy-wide. The integrated light is dominated by these bursty regions, which exhibit strong line emission, with the equivalent width of O
iii
+H
β
reaching up to ∼3000–4000 Å rest frame. Studying these galaxies in an integrated approach yields extremely young inferred ages of the stellar population (<10 Myr), which outshine older stellar populations that are only distinguishable in the spatially resolved maps. This leads to inferring ∼0.5–1 dex lower stellar masses by using single-aperture photometry, when compared to resolved analyses. Such systematics would have strong implications in the shape and evolution of the stellar mass function at these early times, particularly while samples are limited to small numbers of the brightest candidates. Furthermore, the evolved stellar populations revealed in this study imply an extended process of early galaxy formation that could otherwise be hidden behind the light of the most recently formed stars.
We present a new data release from the Fiber Multi-Object Spectrograph (FMOS)-COSMOS survey that contains the measurements of the spectroscopic redshift and flux of rest-frame optical emission lines ...(H , N ii, S ii, Hβ, O iii) for 1931 galaxies out of a total of 5484 objects observed over the 1.7 deg2 COSMOS field. We obtained H- and J-band medium-resolution (R ∼ 3000) spectra with FMOS mounted on the Subaru telescope, which offers an in-fiber line flux sensitivity limit of for an on-source exposure time of 5 hr. The full sample contains the main population of star-forming galaxies at z ∼ 1.6 over the stellar mass range , as well as other subsamples of infrared-luminous galaxies detected by Spitzer and Herschel at the same and lower (z ∼ 0.9) redshifts and X-ray-emitting galaxies detected by Chandra. This paper presents an overview of our spectral analyses, a description of the sample characteristics, and a summary of the basic properties of emission-line galaxies. We use the larger sample to redefine the stellar mass-star formation rate relation based on the dust-corrected H luminosity and find that the individual galaxies are better fit with a parameterization including a bending feature at M* 1010.2 M , and that the intrinsic scatter increases with M* from 0.19 to 0.37 dex. We also confirm with higher confidence that the massive (M* 1010.5 M ) galaxies are chemically mature as much as local galaxies with the same stellar masses, and that the massive galaxies have lower S ii/H ratios for their O iii/Hβ as compared to local galaxies, which is indicative of enhancement in the ionization parameter.
We present new observations, carried out with IRAM NOEMA, of the atomic neutral carbon transitions C
I
(
3
P
1
–
3
P
0
) at 492 GHz and C
I
(
3
P
2
–
3
P
1
) at 809 GHz of GN20, a well-studied ...star-bursting galaxy at
z
= 4.05. The high luminosity line ratio C
I
(
3
P
2
–
3
P
1
) /C
I
(
3
P
1
–
3
P
0
) implies an excitation temperature of 48
+14
−9
K, which is significantly higher than the apparent dust temperature of
T
d
= 33 ± 2 K (
β
= 1.9) derived under the common assumption of an optically thin far-infrared dust emission, but fully consistent with
T
d
= 52 ± 5 K of a general opacity model where the optical depth (
τ
) reaches unity at a wavelength of
λ
0
= 170 ± 23
μ
m. Moreover, the general opacity solution returns a factor of ∼2× lower dust mass and, hence, a lower molecular gas mass for a fixed gas-to-dust ratio, than with the optically thin dust model. The derived properties of GN20 thus provide an appealing solution to the puzzling discovery of starbursts appearing colder than main-sequence galaxies above
z
> 2.5, in addition to a lower dust-to-stellar mass ratio that approaches the physical value predicted for starburst galaxies.
We present a detailed analysis of a large sample of spectroscopically confirmed massive quiescent galaxies (MQGs; log(M*/M ) ∼ 11.5) at z 2. This sample comprises 15 galaxies selected in the COSMOS ...and UDS fields by their bright K-band magnitudes and followed up with Very Large Telescope (VLT) X-shooter spectroscopy and Hubble Space Telescope (HST)/WFC3 HF160W imaging. These observations allow us to unambiguously confirm their redshifts, ascertain their quiescent nature and stellar ages, and reliably assess their internal kinematics and effective radii. We find that these galaxies are compact, consistent with the high-mass end of the stellar mass-size relation for quiescent galaxies at z = 2. Moreover, the distribution of the measured stellar velocity dispersions of the sample is consistent with the most massive local early-type galaxies from the MASSIVE Survey, showing that evolution in these galaxies is dominated by changes in size. The HST images reveal, as surprisingly high, that 40% of the sample has tidal features suggestive of mergers and companions in close proximity, including three galaxies experiencing ongoing major mergers. The absence of velocity dispersion evolution from z = 2 to 0, coupled with a doubling of the stellar mass, with a factor of 4 size increase and the observed disturbed stellar morphologies, supports dry minor mergers as the primary drivers of the evolution of the MQGs over the last 10 billion yr.
Abstract
We study the carbon monoxide (CO) excitation, mean molecular gas density, and interstellar radiation field (ISRF) intensity in a comprehensive sample of 76 galaxies from local to high ...redshift (
z
∼ 0–6), selected based on detections of their CO transitions
J
= 2 → 1 and 5 → 4 and their optical/infrared/(sub)millimeter spectral energy distributions (SEDs). We confirm the existence of a tight correlation between CO excitation as traced by the CO (5–4)
/
(2–1) line ratio
R
52
and the mean ISRF intensity
U
as derived from infrared SED fitting using dust SED templates. By modeling the molecular gas density probability distribution function (PDF) in galaxies and predicting CO line ratios with large velocity gradient radiative transfer calculations, we present a framework linking global CO line ratios to the mean molecular hydrogen gas density
n
H
2
and kinetic temperature
T
kin
. Mapping in this way observed
R
52
ratios to
n
H
2
and
T
kin
probability distributions, we obtain positive
U
–
n
H
2
and
U
–
T
kin
correlations, which imply a scenario in which the ISRF in galaxies is mainly regulated by
T
kin
and (nonlinearly) by
n
H
2
. A small fraction of starburst galaxies showing enhanced
n
H
2
could be due to merger-driven compaction. Our work demonstrates that ISRF and CO excitation are tightly coupled and that density–PDF modeling is a promising tool for probing detailed ISM properties inside galaxies.
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