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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. [ABSTRACT FROM AUTHOR]

We report Atacama Large Millimeter/submillimeter Array observations of CO(8–7), (9–8), , and and NOrthern Extended Millimeter Array observations of CO(5–4), (6–5), (12–11), and (13–12) toward the z = 6.003 quasar SDSS J231038.88+185519.7, aiming to probe the physical conditions of the molecular gas content of this source. We present the best sampled CO spectral line energy distribution (SLED) at z = 6.003, and analyzed it with the radiative transfer code MOLPOP-CEP. Fitting the CO SLED to a one-component model indicates a kinetic temperature Tkin = 228 K, molecular gas density ) = 4.75, and CO column density ; although, a two-component model better fits the data. In either case, the CO SLED is dominated by a “warm” and “dense” component. Compared to samples of local (Ultra) Luminous Infrared Galaxies, starburst galaxies, and high-redshift submillimeter galaxies, J2310+1855 exhibits higher CO excitation at (J ≥ 8), like other high-redshift quasars. The high CO excitation, together with the enhanced , , and ratios, suggests that besides the UV radiation from young massive stars, other mechanisms such as shocks, cosmic-rays, and X-rays might also be responsible for the heating and ionization of the molecular gas. In the nuclear region probed by the molecular emissions lines, any of these mechanisms might be present due to the powerful quasar and the starburst activity. [ABSTRACT FROM AUTHOR]

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 μm, 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 × 10−2M⊙ 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 FROM AUTHOR]

Water (H2O), one of the most ubiquitous molecules in the universe, has bright millimeter-wave emission lines that are easily observed at high redshift with the current generation of instruments. The low-excitation transition of H2O, (νrest = 987.927 GHz), is known to trace the far-infrared (FIR) radiation field independent of the presence of active galactic nuclei (AGNs) over many orders of magnitude in FIR luminosity (). This indicates that this transition arises mainly due to star formation. In this paper, we present spatially (∼0.″5 corresponding to ∼1 kiloparsec) and spectrally resolved (∼100 kms−1) observations of in a sample of four strong gravitationally lensed high-redshift galaxies with the Atacama Large Millimeter/submillimeter Array. In addition to increasing the sample of luminous (>1012L⊙) galaxies observed with H2O, this paper examines the relation on resolved scales for the first time at high redshift. We find that is correlated with on both global and resolved kiloparsec scales within the galaxy in starbursts and AGN with average . We find that the scatter in the observed relation does not obviously correlate with the effective temperature of the dust spectral energy distribution or the molecular gas surface density. This is a first step in developing as a resolved star formation rate calibrator. [ABSTRACT FROM AUTHOR]

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 μm 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 μm dust continuum structure at ∼700 pc (∼0.″12) resolution. We discuss the deficit with a pixellated study of the L[C 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. [ABSTRACT FROM AUTHOR]

In this paper, we provide a physical model for the origin of variations in the shapes and bump strengths of dust attenuation laws in galaxies by combining a large suite of cosmological “zoom-in” galaxy formation simulations with 3D Monte Carlo dust radiative transfer calculations. We model galaxies over three orders of magnitude in stellar mass, ranging from Milky Way–like systems to massive galaxies at high redshift. Critically, for these calculations, we employ a constant underlying dust extinction law in all cases and examine how the role of geometry and radiative transfer effects impacts the resultant attenuation curves. Our main results follow. Despite our usage of a constant dust extinction curve, we find dramatic variations in the derived attenuation laws. The slopes of normalized attenuation laws depend primarily on the complexities of star-to-dust geometry. Increasing fractions of unobscured young stars flatten normalized curves, while increasing fractions of unobscured old stars steepen curves. Similar to the slopes of our model attenuation laws, we find dramatic variation in the 2175 Å ultraviolet bump strength, including a subset of curves with little to no bump. These bump strengths are primarily influenced by the fraction of unobscured O and B stars in our model, with the impact of scattered light having only a secondary effect. Taken together, these results lead to a natural relationship between the attenuation curve slope and 2175 Å bump strength. Finally, we apply these results to a 25 Mpc h−1 box cosmological hydrodynamic simulation in order to model the expected dispersion in attenuation laws at integer redshifts from z = 0 to 6. A significant dispersion is expected at low redshifts and decreases toward z = 6. We provide tabulated results for the best-fit median attenuation curve at all redshifts. [ABSTRACT FROM AUTHOR]

The H2 mass of molecular clouds has traditionally been traced by the CO(J = 1−0) rotational transition line. This said, CO is relatively easily photodissociated and can also be destroyed by cosmic rays, thus rendering some fraction of molecular gas to be “CO-dark.” We investigate the amount and physical properties of CO-dark gas in two z ∼ 0 disk galaxies and develop predictions for the expected intensities of promising alternative tracers ([C i] 609 μm and [C ii] 158 μm emission). We do this by combining cosmological zoom simulations of disk galaxies with thermal-radiative-chemical equilibrium interstellar medium (ISM) calculations to model the predicted H i and H2 abundances and CO (J = 1−0), [C i] 609 μm, and [C ii] 158 μm emission properties. Our model treats the ISM as a collection of radially stratified clouds whose properties are dictated by their volume and column densities, the gas-phase metallicity, and the interstellar radiation field (ISRF) and CR ionization rates. Our main results follow. Adopting an observationally motivated definition of CO-dark gas, i.e., H2 gas with WCO < 0.1 K km s−1, we find that a significant amount (≳50%) of the total H2 mass lies in CO-dark gas, most of which is diffuse gas, poorly shielded due to low dust column density. The CO-dark molecular gas tends to be dominated by [C ii], though [C i] also serves as a bright tracer of the dark gas in many instances. At the same time, [C ii] also tends to trace neutral atomic gas. As a result, when we quantify the conversion factors for the three carbon-based tracers of molecular gas, we find that [C i] suffers the least contamination from diffuse atomic gas and is relatively insensitive to secondary parameters. [ABSTRACT FROM AUTHOR]

Post-starburst or “E + A” galaxies are rapidly transitioning from star-forming to quiescence. While the current star formation rate (SFR) of post-starbursts is already at the level of early-type galaxies, we recently discovered that many have large CO-traced molecular gas reservoirs consistent with normal star-forming galaxies. These observations raise the question of why these galaxies have such low SFRs. Here we present an ALMA search for the denser gas traced by HCN (1–0) and HCO+ (1–0) in two CO-luminous, quiescent post-starburst galaxies. Intriguingly, we fail to detect either molecule. The upper limits are consistent with the low SFRs and with early-type galaxies. The HCN/CO luminosity ratio upper limits are low compared to star-forming and even many early-type galaxies. This implied low dense gas mass fraction explains the low SFRs relative to the CO-traced molecular gas and suggests that the state of the gas in post-starburst galaxies is unusual, with some mechanism inhibiting its collapse to denser states. We conclude that post-starbursts galaxies are now quiescent because little dense gas is available, in contrast to the significant CO-traced lower density gas reservoirs that still remain. [ABSTRACT FROM AUTHOR]

Of the almost 40 star-forming galaxies at (not counting quasi-stellar objects) observed in to date, nearly half are either very faint in or not detected at all, and fall well below expectations based on locally derived relations between star formation rate and luminosity. This has raised questions as to how reliable is as a tracer of star formation activity at these epochs and how factors such as metallicity might affect the emission. Combining cosmological zoom simulations of galaxies with SÍGAME (SImulator of GAlaxy Millimeter/submillimeter Emission), we modeled the multiphased interstellar medium (ISM) and its emission in , as well as in [O i] and [O iii], from 30 main-sequence galaxies at with star formation rates ∼3–23 , stellar masses , and metallicities . The simulations are able to reproduce the aforementioned faintness of some normal star-forming galaxy sources at . In terms of [O i] and [O iii], very few observations are available at , but our simulations match two of the three existing detections of [O iii] and are furthermore roughly consistent with the [O i] and [O iii] luminosity relations with star formation rate observed for local starburst galaxies. We find that the emission is dominated by the diffuse ionized gas phase and molecular clouds, which on average contribute ∼66% and ∼27%, respectively. The molecular gas, which constitutes only of the total gas mass, is thus a more efficient emitter of than the ionized gas, which makes up ∼85% of the total gas mass. A principal component analysis shows that the luminosity correlates with the star formation activity of a galaxy as well as its average metallicity. The low metallicities of our simulations together with their low molecular gas mass fractions can account for their faintness, and we suggest that these factors may also be responsible for the -faint normal galaxies observed at these early epochs. [ABSTRACT FROM AUTHOR]

We present new Atacama Large Millimeter/submillimeter Array (ALMA) observations of the dust continuum and [C ii] 158 μm fine structure line emission toward a far-infrared-luminous quasar, ULAS J131911.29+095051.4 at z = 6.13, and combine the new Cycle 1 data with ALMA Cycle 0 data. The combined data have an angular resolution of ∼0.″3, and resolve both the dust continuum and the [C ii] line emission on a few kiloparsec scales. The [C ii] line emission is more irregular than that of the dust continuum emission, which suggests different distributions between the dust and the [C ii]-emitting gas. The combined data confirm the [C ii] velocity gradient that we had previously detected in a lower-resolution ALMA image from the Cycle 0 data alone. We apply a tilted ring model to the [C ii] velocity map to obtain a rotation curve, and constrain the circular velocity to be 427 ± 55 km s−1 at a radius of 3.2 kpc with an inclination angle of 34°. We measure the dynamical mass within the 3.2 kpc region to be . This yields a black-hole and host galaxy mass ratio of , which is about times higher than that of the present-day / ratio. This suggests that the supermassive black hole grows the bulk of its mass before the formation of most of the stellar mass in this quasar host galaxy in the early universe. [ABSTRACT FROM AUTHOR]

Recent observations have shown that the characteristic luminosity of the rest-frame ultraviolet (UV) luminosity function does not significantly evolve at 4 < z < 7 and is approximately We investigate this apparent non-evolution by examining a sample of 173 bright, MUV < −21 galaxies at z = 4–7, analyzing their stellar populations and host halo masses. Including deep Spitzer/IRAC imaging to constrain the rest-frame optical light, we find that galaxies at z = 4–7 have similar stellar masses of log(M/M⊙) = 9.6–9.9 and are thus relatively massive for these high redshifts. However, bright galaxies at z = 4–7 are less massive and have younger inferred ages than similarly bright galaxies at z = 2–3, even though the two populations have similar star formation rates and levels of dust attenuation for a fixed dust-attenuation curve. Matching the abundances of these bright z = 4–7 galaxies to halo mass functions from the Bolshoi ΛCDM simulation implies that the typical halo masses in galaxies decrease from log(Mh/M⊙) = 11.9 at z = 4 to log(Mh/M⊙) = 11.4 at z = 7. Thus, although we are studying galaxies at a similar stellar mass across multiple redshifts, these galaxies live in lower mass halos at higher redshift. The stellar baryon fraction in galaxies in units of the cosmic mean Ωb/Ωm rises from 5.1% at z = 4 to 11.7% at z = 7; this evolution is significant at the ∼3σ level. This rise does not agree with simple expectations of how galaxies grow, and implies that some effect, perhaps a diminishing efficiency of feedback, is allowing a higher fraction of available baryons to be converted into stars at high redshifts. [ABSTRACT FROM AUTHOR]

We present SÍGAME simulations of the 157.7 μm fine structure line emission from cosmological smoothed particle hydrodynamics simulations of seven main sequence galaxies at z = 2. Using sub-grid physics prescriptions the gas in our simulations is modeled as a multi-phased interstellar medium comprised of molecular gas residing in giant molecular clouds, an atomic gas phase associated with photo-dissociation regions (PDRs) at the cloud surfaces, and a diffuse, ionized gas phase. Adopting logotropic cloud density profiles and accounting for heating by the local FUV radiation field and cosmic rays by scaling both with local star formation rate (SFR) volume density, we calculate the emission using a photon escape probability formalism. The emission peaks in the central of our galaxies as do the SFR radial profiles, with most () originating in the molecular gas phase, whereas further out (), the atomic/PDR gas dominates () the emission, no longer tracing ongoing star formation. Throughout, the ionized gas contribution is negligible (). The luminosity versus SFR (–SFR) relationship, integrated as well as spatially resolved (on scales of 1 kpc), delineated by our simulated galaxies is in good agreement with the corresponding relations observed locally and at high redshifts. In our simulations, the molecular gas dominates the budget at ( ), while atomic/PDR gas takes over at lower SFRs, suggesting a picture in which predominantly traces the molecular gas in high-density/pressure regions where star formation is ongoing, and otherwise reveals the atomic/PDR gas phase. [ABSTRACT FROM AUTHOR]