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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 (February 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. Multiphase ISM in the z = 5.7 Hyperluminous Starburst SPT 0346–52

   https://doi.org/10.3847/1538-4357/ac58f9  

   Litke, Katrina C.; Marrone, Daniel P.; Aravena, Manuel; Béthermin, Matthieu; Chapman, Scott C.; Dong, Chenxing; Hayward, Christopher C.; Hill, Ryley; Jarugula, Sreevani; Malkan, Matthew A.; et al (April 2022, The Astrophysical Journal)

   Abstract With Σ SFR ∼ 4200 M ⊙ yr −1 kpc −2 , SPT 0346–52 ( z = 5.7) is the most intensely star-forming galaxy discovered by the South Pole Telescope. In this paper, we expand on previous spatially resolved studies, using ALMA observations of dust continuum, [N ii ] 205 μ m, [C ii ] 158 μ m, [O i ] 146 μ m, and undetected [N ii ] 122 μ m and [O i ] 63 μ m emission to study the multiphase interstellar medium (ISM) in SPT 0346–52. We use pixelated, visibility-based lens modeling to reconstruct the source-plane emission. We also model the source-plane emission using the photoionization code cloudy and find a supersolar metallicity system. We calculate T dust = 48.3 K and λ peak = 80 μ m and see line deficits in all five lines. The ionized gas is less dense than comparable galaxies, with n e < 32 cm −3 , while ∼20% of the [C ii ] 158 μ m emission originates from the ionized phase of the ISM. We also calculate the masses of several phases of the ISM. We find that molecular gas dominates the mass of the ISM in SPT 0346–52, with the molecular gas mass ∼4× higher than the neutral atomic gas mass and ∼100× higher than the ionized gas mass. 

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3. 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 (October 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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4. Emission-line Ratios and Ionization Conditions of CEERS Star-forming Galaxies with JWST/NIRSpec

   https://doi.org/10.3847/2515-5172/ad888e  

   Gupta, Ansh R; Kirkpatrick, Allison; Fernández, Vital; Arrabal_Haro, Pablo; Backhaus, Bren E; Cleri, Nikko J; Grogin, Norman A; Koekemoer, Anton M (October 2024, Research Notes of the AAS)

   Abstract Galaxy emission-line fluxes can constrain star formation rates (SFRs) and interstellar medium (ISM) ionization. We investigate rest-frame optical emission lines of 71 star-forming galaxies (SFGs) at redshift 0.7 < z < 7 using JWST/NIRSpec measurements from the Cosmic Evolution Early Release Science survey. We use Hαto measure SFR and utilize Hubble Space Telescope CANDELS stellar mass estimates to determine specific SFR (sSFR) and compare with the SFG main sequence (MS). We create [O iii]λ5008/Hβversus [Ne iii]λ3870/[O ii]λ3728 line ratio diagrams. The line ratios appear to correlate with sSFR, and our results suggest that sSFR is the parameter that governs ionization conditions rather than SFR or a galaxy’s distance from the MS. These measurements reveal a rich diversity of ISM conditions and physical galaxy properties throughout cosmic time. 

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5. The Physical Conditions of Emission-line Galaxies at Cosmic Dawn from JWST/NIRSpec Spectroscopy in the SMACS 0723 Early Release Observations

   https://doi.org/10.3847/1538-4357/acba8a  

   Trump, Jonathan R.; Haro, Pablo Arrabal; Simons, Raymond C.; Backhaus, Bren E.; Amorín, Ricardo O.; Dickinson, Mark; Fernández, Vital; Papovich, Casey; Nicholls, David C.; Kewley, Lisa J.; et al (March 2023, The Astrophysical Journal)

   Abstract We present rest-frame optical emission-line flux ratio measurements for five z > 5 galaxies observed by the James Webb Space Telescope Near-Infared Spectrograph (NIRSpec) in the SMACS 0723 Early Release Observations. We add several quality-control and post-processing steps to the NIRSpec pipeline reduction products in order to ensure reliable relative flux calibration of emission lines that are closely separated in wavelength, despite the uncertain absolute spectrophotometry of the current version of the reductions. Compared to z ∼ 3 galaxies in the literature, the z > 5 galaxies have similar [O iii ] λ 5008/H β ratios, similar [O iii ] λ 4364/H γ ratios, and higher (∼0.5 dex) [Ne III ] λ 3870/[O II ] λ 3728 ratios. We compare the observations to MAPPINGS V photoionization models and find that the measured [Ne III ] λ 3870/[O II ] λ 3728, [O iii ] λ 4364/H γ , and [O iii ] λ 5008/H β emission-line ratios are consistent with an interstellar medium (ISM) that has very high ionization ( log ( Q ) ≃ 8 − 9 , units of cm s −1 ), low metallicity ( Z / Z ⊙ ≲ 0.2), and very high pressure ( log ( P / k ) ≃ 8 − 9 , units of cm −3 ). The combination of [O iii ] λ 4364/H γ and [O iii ] λ (4960 + 5008)/H β line ratios indicate very high electron temperatures of 4.1 < log ( T e / K ) < 4.4 , further implying metallicities of Z / Z ⊙ ≲ 0.2 with the application of low-redshift calibrations for “ T e -based” metallicities. These observations represent a tantalizing new view of the physical conditions of the ISM in galaxies at cosmic dawn. 

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