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1. The ALPINE-ALMA [C  ii ] survey: Investigation of 10 galaxies at z ∼ 4.5 with [O  ii ] and [C  ii ] line emission − ISM properties and [O  ii ]−SFR relation

   https://doi.org/10.1093/mnras/stac071  

   Vanderhoof, Brittany N.; Faisst, A. L.; Shen, L.; Lemaux, B. C.; Béthermin, M.; Capak, P. L.; Cassata, P.; Le Fèvre, O.; Schaerer, D.; Silverman, J.; et al (January 2022, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We present 10 main-sequence ALPINE galaxies (log (M/M⊙) = 9.2−11.1 and $${\rm SFR}=23-190\, {\rm M_{\odot }\, yr^{-1}}$$) at z ∼ 4.5 with optical [O ii] measurements from Keck/MOSFIRE spectroscopy and Subaru/MOIRCS narrow-band imaging. This is the largest such multiwavelength sample at these redshifts, combining various measurements in the ultraviolet, optical, and far-infrared including [C ii]158 $$\mu$$m line emission and dust continuum from ALMA and H α emission from Spitzer photometry. For the first time, this unique sample allows us to analyse the relation between [O ii] and total star-formation rate (SFR) and the interstellar medium (ISM) properties via [O ii]/[C ii] and [O ii]/H α luminosity ratios at z ∼ 4.5. The [O ii]−SFR relation at z ∼ 4.5 cannot be described using standard local descriptions, but is consistent with a metal-dependent relation assuming metallicities around $$50{{\ \rm per\ cent}}$$ solar. To explain the measured dust-corrected luminosity ratios of $$\log (L_{\rm [OII]}/L_{\rm [CII]}) \sim 0.98^{+0.21}_{-0.22}$$ and $$\log (L_{\rm [OII]}/L_{\rm H\alpha }) \sim -0.22^{+0.13}_{-0.15}$$ for our sample, ionization parameters log (U) < −2 and electron densities $$\log (\rm n_e / {\rm [cm^{-3}]}) \sim 2.5-3$$ are required. The former is consistent with galaxies at z ∼ 2−3, however lower than at z > 6. The latter may be slightly higher than expected given the galaxies’ specific SFR. The analysis of this pilot sample suggests that typical log (M/M⊙) > 9 galaxies at z ∼ 4.5 to have broadly similar ISM properties as their descendants at z ∼ 2 and suggest a strong evolution of ISM properties since the epoch of reionization at z > 6. 

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2. [CII] 158 μ m emission as an indicator of galaxy star formation rate

   https://doi.org/10.1093/mnras/stad3792  

   Liang, Lichen; Feldmann, Robert; Murray, Norman; Narayanan, Desika; Hayward, Christopher C.; Anglés-Alcázar, Daniel; Bassini, Luigi; Richings, Alexander J.; Faucher-Giguère, Claude-André; Chung, Dongwoo T.; et al (December 2023, Monthly Notices of the Royal Astronomical Society)

   Abstract Observations of local star-forming galaxies (SFGs) show a tight correlation between their singly ionized carbon line luminosity ($$L_{\rm [C\, \small {II}]}$$) and star formation rate (SFR), suggesting that $$L_{\rm [C\, \small {II}]}$$ may be a useful SFR tracer for galaxies. Some other galaxy populations, however, are found to have lower $$L_{\rm [C\, \small {II}]}{}/{}\rm SFR$$ than local SFGs, including the infrared-luminous, starburst galaxies at low and high redshifts as well as some moderately star-forming galaxies at the epoch of re-ionization (EoR). The origins of this ‘$$\rm [C\, \small {II}]$$ deficit’ is unclear. In this work, we study the $$L_{\rm [C\, \small {II}]}$$-SFR relation of galaxies using a sample of z = 0 − 8 galaxies with M* ≈ 107 − 5 × 1011 M⊙ extracted from cosmological volume and zoom-in simulations from the Feedback in Realistic Environments (fire) project. We find a simple analytic expression for $$L_{\rm [C\, \small {II}]}$$/SFR of galaxies in terms of the following parameters: mass fraction of $$\rm [C\, \small {II}]$$-emitting gas ($$f_{\rm [C\, \small {II}]}$$), gas metallicity (Zgas), gas density (ngas) and gas depletion time ($$t_{\rm dep}{}={}M_{\rm gas}{}/{}\rm SFR$$). We find two distinct physical regimes: $$\rm H_2$$-rich galaxies where tdep is the main driver of the $$\rm [C\, \small {II}]$$ deficit and $$\rm H_2$$-poor galaxies where Zgas is the main driver. The observed $$\rm [C\, \small {II}]$$ deficit of IR-luminous galaxies and early EoR galaxies, corresponding to the two different regimes, is due to short gas depletion time and low gas metallicity, respectively. Our result indicates that the $$\rm [C\, \small {II}]$$ deficit is a common phenomenon of galaxies, and caution needs to be taken when applying a constant $$L_{\rm [C\, \small {II}]}$$-to-SFR conversion factor derived from local SFGs to estimate cosmic SFR density at high redshifts and interpret data from upcoming $$\rm [C\, \small {II}]$$ line intensity mapping experiments. 

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3. Molecular gas in AzTEC/C159: a star-forming disk galaxy 1.3Gyr after the Big Bang

   Jiménez-Andrade, E. F.; Magnelli, B.; Karim, A.; Jones, G. C.; Carilli, C. L.; Romano-Díaz, E.; Gómez-Guijarro, C.; Toft, S.; Bertoldi, F.; Riechers, D. A.; et al (January 2018, Astronomy & astrophysics)

   We studied the molecular gas properties of AzTEC/C159, a star-forming disk galaxy at $z=4.567$. We secured $$^{12}$$CO molecular line detections for the $$J=2\to1$$ and $$J=5\to4$$ transitions using the Karl G. Jansky VLA and the NOEMA interferometer. The broad (FWHM$$\sim750\,{\rm km\,s}^{-1}$$) and tentative double-peaked profiles of both $$^{12}$$CO lines are consistent with an extended molecular gas reservoir, which is distributed in a rotating disk as previously revealed from [CII] 158$$\mu$$m line observations. Based on the $$^{12}$$CO(2$$\to$$1) emission line we derived $$L'_{\rm{CO}}=(3.4\pm0.6)\times10^{10}{\rm \,K\,km\,s}^{-1}{\rm \,pc}^{2}$$, that yields a molecular gas mass of $$M_{\rm H_2 }(\alpha_{\rm CO}/4.3)=(1.5\pm0.3)\times 10^{11}{\rm M}_\odot$$ and unveils a gas-rich system with $$\mu_{\rm gas}(\alpha_{\rm CO}/4.3)\equiv M_{\rm H_2}/M_\star=3.3\pm0.7$$. The extreme star formation efficiency (SFE) of AzTEC/C159, parametrized by the ratio $$L_{\rm{IR}}/L'_{\rm{CO}}=(216\pm80)\, {\rm L}_{\odot}{\rm \,(K\,km\,s}^{-1}{\rm \,pc}^{2})^{-1}$$, is comparable to merger-driven starbursts such as local ultra-luminous infrared galaxies (ULIRGs) and SMGs. Likewise, the $$^{12}$$CO(5$$\to$$4)/CO(2$$\to$$1) line brightness temperature ratio of $$r_{52}= 0.55\pm 0.15$$ is consistent with high excitation conditions, similar to that observed in SMGs. We constrained the value for the $$L'_{\text{CO}}-{\rm H}_2$$ mass conversion factor in AzTEC/C159, i.e. $$\alpha_{\text{CO}}=3.9^{+2.7}_{-1.3}{\rm \,M}_{\odot}{\rm \,K}^{-1}{\rm \,km}^{-1}{\rm \,s\,pc}^{-2}$$, that is consistent with a self-gravitating molecular gas distribution as observed in local star-forming disk galaxies. Cold gas streams from cosmological filaments might be fueling a gravitationally unstable gas-rich disk in AzTEC/C159, which breaks into giant clumps forming stars as efficiently as in merger-driven systems and generate high gas excitation. 

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4. The kinematics of massive high-redshift dusty star-forming galaxies

   https://doi.org/10.1093/mnras/stae2760  

   Amvrosiadis, A.; Wardlow, J_L; Birkin, J_E; Smail, I.; Swinbank, A_M; Nightingale, J.; Bertoldi, F.; Brandt, W_N; Casey, C_M; Chapman, S_C; et al (December 2024, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We present a new method for modelling the kinematics of galaxies from interferometric observations by performing the optimization of the kinematic model parameters directly in visibility space instead of the conventional approach of fitting velocity fields produced with the clean algorithm in real-space. We demonstrate our method on Atacama Large Millimeter/submillimeter Array (ALMA) observations of $$^{12}$$CO (2–1), (3–2), or (4–3) emission lines from an initial sample of 30 massive 850 $$\mu$$m-selected dusty star-forming galaxies with far-infrared luminosities $$\gtrsim$$\, 10^{12}$$ L$$_{\odot }$$ in the redshift range $$z \sim$$ 1.2–4.7. Using the results from our modelling analysis for the 12 of the 20 sources with the highest signal-to-noise emission lines that show disc-like kinematics, we conclude the following: (i) our sample prefers a CO-to-$$H_2$$ conversion factor, of $$\alpha _{\rm CO} = 0.74 \pm 0.37$$; (ii) these far-infrared luminous galaxies follow a similar Tully–Fisher relation between the circular velocity, $$V_{\rm circ}$$, and baryonic mass, $$M_{\rm b}$$, as less strongly star-forming samples at high redshift, but extend this relation to much higher masses – showing that these are some of the most massive disc-like galaxies in the Universe; (iii) finally, we demonstrate support for an evolutionary link between massive high-redshift dusty star-forming galaxies and the formation of local early-type galaxies using the both the distributions of the baryonic and kinematic masses of these two populations on the $$M_{\rm b}$$ – $$\sigma$$ plane and their relative space densities. 

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5. The effects of local stellar radiation and dust depletion on non-equilibrium interstellar chemistry

   https://doi.org/10.1093/mnras/stac2338  

   Richings, Alexander J.; Faucher-Giguère, Claude-André; Gurvich, Alexander B.; Schaye, Joop; Hayward, Christopher C. (August 2022, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Interstellar chemistry is important for galaxy formation, as it determines the rate at which gas can cool, and enables us to make predictions for observable spectroscopic lines from ions and molecules. We explore two central aspects of modelling the chemistry of the interstellar medium (ISM): (1) the effects of local stellar radiation, which ionizes and heats the gas, and (2) the depletion of metals on to dust grains, which reduces the abundance of metals in the gas phase. We run high-resolution (400 M⊙ per baryonic particle) simulations of isolated disc galaxies, from dwarfs to Milky Way-mass, using the fire galaxy formation models together with the chimes non-equilibrium chemistry and cooling module. In our fiducial model, we couple the chemistry to the stellar fluxes calculated from star particles using an approximate radiative transfer scheme; and we implement an empirical density-dependent prescription for metal depletion. For comparison, we also run simulations with a spatially uniform radiation field, and without metal depletion. Our fiducial model broadly reproduces observed trends in H i and H2 mass with stellar mass, and in line luminosity versus star formation rate for [C ii]$$_{158 \rm {\mu m}}$$, [O i]$$_{63 \rm {\mu m}}$$, [O iii]$$_{88 \rm {\mu m}}$$, [N ii]$$_{122 \rm {\mu m}}$$, and H α6563Å. Our simulations with a uniform radiation field predict fainter luminosities, by up to an order of magnitude for [O iii]$$_{88 \rm {\mu m}}$$ and H α6563Å, while ignoring metal depletion increases the luminosity of carbon and oxygen lines by a factor ≈ 2. However, the overall evolution of the galaxy is not strongly affected by local stellar fluxes or metal depletion, except in dwarf galaxies where the inclusion of local fluxes leads to weaker outflows and hence higher gas fractions. 

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