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.
SPT0346-52 is one of the most most luminous and intensely star-forming galaxies in the universe, with and . In this paper, we present ALMA observations of the 158 m emission line in this z = 5.7 ...dusty star-forming galaxy. We use a pixellated lensing reconstruction code to spatially and kinematically resolve the source-plane and rest-frame 158 m dust continuum structure at ∼700 pc (∼0 12) resolution. We discuss the deficit with a pixellated study of the LC ii/LFIR ratio in the source plane. We find that individual pixels within the galaxy follow the same trend found using unresolved observations of other galaxies, indicating that the deficit arises on scales 700 pc. The lensing reconstruction reveals two spatially and kinematically separated components (∼1 kpc and ∼500 km s−1 apart) connected by a bridge of gas. Both components are found to be globally unstable, with Toomre Q instability parameters everywhere. We argue that SPT0346-52 is undergoing a major merger, which is likely driving the intense and compact star formation.
We study the luminosity line ratio in a sample of nearby (z < 0.05) galaxies: 25 star-forming galaxies (SFGs) from the xCOLD GASS survey, 36 hard X-ray-selected active galactic nucleus (AGN) host ...galaxies from the BAT AGN Spectroscopic Survey, and 37 infrared-luminous galaxies from the SCUBA Local Universe Galaxy Survey. We find a trend for r31 to increase with star formation efficiency (SFE). We model r31 using the UCL-PDR code and find that the gas density is the main parameter responsible for the variation of r31, while the interstellar radiation field and cosmic-ray ionization rate play only a minor role. We interpret these results to indicate a relation between SFE and gas density. We do not find a difference in the r31 value of SFGs and AGN host galaxies, when the galaxies are matched in SSFR (〈r31〉 = 0.52 0.04 for SFGs and 〈r31〉 = 0.53 0.06 for AGN hosts). According to the results of the UCL-PDR models, the X-rays can contribute to the enhancement of the CO line ratio, but only for strong X-ray fluxes and for high gas density (nH > 104 cm−3). We find a mild tightening of the Kennicutt-Schmidt relation when we use the molecular gas mass surface density traced by CO(3-2) (Pearson correlation coefficient R = 0.83), instead of the molecular gas mass surface density traced by CO(1-0) (R = 0.78), but the increase in correlation is not statistically significant (p-value = 0.06). This suggests that the CO(3-2) line can be reliably used to study the relation between SFR and molecular gas for normal SFGs at high redshift and to compare it with studies of low-redshift galaxies, as is common practice.
ABSTRACT
We present an extensive ALMA spectroscopic follow-up programme of the $z\, {=}\, 4.3$ structure SPT2349–56, one of the most actively star-forming protocluster cores known, to identify ...additional members using their C ii 158 μm and CO(4–3) lines. In addition to robustly detecting the 14 previously published galaxies in this structure, we identify a further 15 associated galaxies at $z\, {=}\, 4.3$, resolving 55$\, {\pm }\,$5 per cent of the 870 μm flux density at 0.5 arcsec resolution compared to 21 arcsec single-dish data. These galaxies are distributed into a central core containing 23 galaxies extending out to 300 kpc in diameter, and a northern extension, offset from the core by 400 kpc, containing three galaxies. We discovered three additional galaxies in a red Herschel-SPIRE source 1.5 Mpc from the main structure, suggesting the existence of many other sources at the same redshift as SPT2349–56 that are not yet detected in the limited coverage of our data. An analysis of the velocity distribution of the central galaxies indicates that this region may be virialized with a mass of (9$\pm 5)\, {\times }\, 10^{12}$ M⊙, while the two offset galaxy groups are about 30 and 60 per cent less massive and show significant velocity offsets from the central group. We calculate the C ii and far-infrared number counts, and find evidence for a break in the C ii luminosity function. We estimate the average SFR density within the region of SPT2349–56 containing single-dish emission (a proper diameter of 720 kpc), assuming spherical symmetry, to be roughly 4$\, {\times }\, 10^4$ M⊙ yr−1 Mpc−3; this may be an order of magnitude greater than the most extreme examples seen in simulations.
Abstract
SPT0311-58 is the most massive infrared luminous system discovered so far during the Epoch of Reionization (EoR). In this paper, we present a detailed analysis of the molecular interstellar ...medium at
z
= 6.9, through high resolution observations of the CO(6–5), CO(7–6), CO(10–9), C
i
(2–1), and p‐H
2
O(2
1,1
−2
0,2
) lines and dust continuum emissions with the Atacama Large Millimeter/submillimeter Array. The system consists of a pair of intensely star-forming, gravitationally lensed galaxies (labeled West and East). The intrinsic far-infrared luminosity is (16 ± 4) × 10
12
L
⊙
in West and (27 ± 4) × 10
11
L
⊙
in East. We model the dust, CO, and C
i
using non-local thermodynamic equilibrium radiative transfer models and estimate the intrinsic gas mass to be (5.4 ± 3.4) × 10
11
M
⊙
in West and (3.1 ± 2.7) × 10
10
M
⊙
in East. We find that the CO spectral line energy distribution in West and East are typical of high-redshift submillimeter galaxies (SMGs). The CO-to-H
2
conversion factor (
α
CO
) and the gas depletion timescales estimated from the model are consistent with the high-redshift SMGs in the literature within the uncertainties. We find no evidence of evolution of depletion time with redshift in SMGs at
z
> 3. This is the most detailed study of molecular gas content of a galaxy in the EoR to date, with the most distant detection of H
2
O in a galaxy without any evidence for active galactic nuclei in the literature.
Abstract
We conduct a systematic search for protocluster candidates at
z
≥ 6 in the Cosmic Evolution Survey (COSMOS) field using the recently released COSMOS2020 source catalog. We select galaxies ...using a number of selection criteria to obtain a sample of galaxies that have a high probability of being inside a given redshift bin. We then apply overdensity analysis to the bins using two density estimators, a Weighted Adaptive Kernel estimator and a Weighted Voronoi Tessellation estimator. We have found 15 significant (>4
σ
) candidate galaxy overdensities across the redshift range 6 ≤
z
≤ 7.7. The majority of the galaxies appear to be on the galaxy main sequence at their respective epochs. We use multiple stellar-mass-to-halo-mass conversion methods to obtain a range of dark matter halo mass estimates for the overdensities in the range of ∼10
11
–10
13
M
⊙
, at the respective redshifts of the overdensities. The number and the masses of the halos associated with our protocluster candidates are consistent with what is expected from the area of a COSMOS-like survey in a standard Λ cold dark matter cosmology. Through comparison with simulation, we expect that all of the overdensities at
z
≃ 6 will evolve into Virgo-/Coma-like clusters at present (i.e., with masses ∼10
14
–10
15
M
⊙
). Compared to other overdensities identified at
z
≥ 6 via narrowband selection techniques, the overdensities presented appear to have ∼10× higher stellar masses and star formation rates (SFRs). We compare the evolution in the total SFR and stellar mass content of the protocluster candidates across the redshift range 6 ≤
z
≤ 7.7 and find agreement with the total average SFR from simulations.
Abstract
One of the most fundamental baryonic matter components of galaxies is the neutral atomic hydrogen (H
i
). At low redshifts, this component can be traced directly through the 21 cm ...transition, but to infer the H
i
gas content of the most distant galaxies, a viable tracer is needed. We here investigate the fidelity of the fine-structure transition of the (
2
P
3/2
−
2
P
1/3
) transition of singly ionized carbon C
ii
at 158
μ
m as a proxy for H
i
in a set simulated galaxies at
z
≈ 6, following the work by Heintz et al. We select 11,125 star-forming galaxies from the
simba
simulations, with far-infrared line emissions postprocessed and modeled within the S
igame
framework. We find a strong connection between C
ii
and H
i
, with the relation between this C
ii
-to-H
i
relation (
β
C
II
) being anticorrelated with the gas-phase metallicity of the simulated galaxies. We further use these simulations to make predictions for the total baryonic matter content of galaxies at
z
≈ 6, and specifically the H
i
gas mass fraction. We find mean values of
M
H I
/
M
⋆
= 1.4 and
M
H I
/
M
bar,tot
= 0.45. These results provide strong evidence for H
i
being the dominant baryonic matter component by mass in galaxies at
z
≈ 6.
ABSTRACT
Measuring the environments of massive galaxies at high redshift is crucial to understanding galaxy evolution and the conditions that gave rise to the distribution of matter we see in the ...Universe today. While high-z radio galaxies (HzRGs) and quasars tend to reside in protocluster-like systems, the environments of their radio-quiet counterparts are relatively unexplored, particularly in the submillimetre, which traces dust-obscured star formation. In this study, we search for 850 μm-selected submillimetre galaxies (SMGs) in the environments of massive ($M_{\star }$$\gt 10^{11}$${\rm M}_{\odot }$), radio-quiet ($L_{500 {\rm MHz}}$$\lesssim 10^{25}$ WHz$^{-1}$) galaxies at $z \sim 1\!-\!3$ using data from the SCUBA-2 COSMOS (S2COSMOS) survey. By constructing number counts in circular regions of radius 1–6 arcmin and comparing with blank-field measurements, we find no significant overdensities of SMGs around massive radio-quiet galaxies at any of these scales, despite being sensitive down to overdensities of $\delta \sim 0.4$. To probe deeper than the catalogue we also examine the distribution of peaks in the SCUBA-2 signal-to-noise (SNR) map, which reveals only tentative signs of any difference in the SMG densities of the radio-quiet galaxy environments compared to the blank field, and only on smaller scales (1 arcmin radii, corresponding to $\sim 0.5$ Mpc) and higher SNR thresholds. We conclude that massive, radio-quiet galaxies at cosmic noon are typically in environments with $\delta \lesssim 0.4$, which are either consistent with the blank field or contain only weak overdensities spanning sub-Mpc scales. The contrast between our results and studies of HzRGs with similar stellar masses and redshifts implies an intrinsic link between the wide-field environment and the radio luminosity of the active galactic nucleus at high redshift.
ABSTRACT
Using the First Light And Reionisation Epoch Simulations, a suite of hydrodynamical simulations, we explore the consequences of a realistic model for star–dust geometry on the observed ...properties of galaxies. We find that the ultraviolet (UV) attenuation declines rapidly from the central regions of galaxies, and bright galaxies have spatially extended star formation that suffers less obscuration than their fainter counterparts, demonstrating a non-linear relationship between the UV luminosity and the UV attenuation, giving a double power-law shape to the UVLF. Spatially distinct stellar populations within galaxies experience a wide range of dust attenuation due to variations in the dust optical depth along their line of sight, which can range from completely dust obscured to being fully unobscured. The overall attenuation curve of a galaxy is then a complex combination of various lines of sight within the galaxy. We explore the manifestation of this effect to study the reliability of line ratios to infer galaxy properties, in particular, the Balmer decrement and the Baldwin, Phillips, and Terlevich (BPT) diagram. We find the Balmer decrement predicted Balmer-line attenuation to be higher (factor of 1 to ≳ 10) than expected from commonly used attenuation curves. The observed BPT line ratios deviate from their intrinsic values median difference of 0.08 (0.02) and standard deviation of 0.2 (0.05) for log10(N${\small II}\lambda 6585/$Hα) (log10(O iiiλ5008/Hβ). Finally, we explore the variation in observed properties (UV attenuation, UV slope, and Balmer decrement) with viewing angle, finding average differences of ∼0.3 mag in the UV attenuation.
ABSTRACT We performed a comprehensive stacking analysis on ∼14,200 quiescent galaxy (QG) candidates at z = 0-3 across mid-, far-infrared (MIR and FIR), and radio wavelengths. Identified via their ...rest-frame NUV − r and r − J colors, the QG candidates ( ) have drastically different IR and radio properties depending on their 24 m emission strength. The fraction of QG candidates with strong 24 m emission (equivalent to inferred star formation rates SFR , hereafter "IR-bright") increases with redshift and peaks at 15%, and their stacked MIPS 24 m, Herschel (PACS and SPIRE) and VLA emissions are consistent with being star-forming galaxies (SFGs). In contrast, the majority of QG candidates are faint or undetected at 24 m individually (i.e., SFR24 < 100 M yr−1, hereafter "IR-faint"). Their low dust-obscured SFRs derived from Herschel stacking (SFRH 3, 15, 50 M yr−1 out to z ∼ 1, 2, 3) are >2.5-12.5× lower than compared to SFGs. This is consistent with the quiescence, as expected from their low unobscured SFRs, as inferred from modeling their ultraviolet-to-NIR photometry. The discrepancy between the LIR derived from stacking Herschel and 24 m indicates that IR-faint QGs have dust SEDs that are different from those of SFGs. For the most massive ( ) IR-faint QGs at z < 1.5, the stacked 1.4 GHz emission is in excess of that expected from other SFR indicators, suggesting a widespread presence of low-luminosity active galactic nuclei. Our results reaffirm the existence of a significant population of QGs out to z = 3, thus corroborating the need to quench star formation in galaxies at early epochs.
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![Spatially Resolved [C ii] E...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-637X_2041-8205_1538-4357/small "Spatially Resolved [C ii] Emission in SPT0346-52: A Hyper-starburst Galaxy Merger at z ∼ 5.7")
![Investigating the [C ii]-to...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/2041-8205_2041-8213/small "Investigating the [C ii]-to-H i Conversion Factor and the H i Gas Budget of Galaxies at z ≈ 6 with Hydrodynamic Simulations")
