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1. On the dust temperatures of high-redshift galaxies

   https://doi.org/10.1093/mnras/stz2134  

   Liang, Lichen; Feldmann, Robert; Kereš, Dušan; Scoville, Nick Z; Hayward, Christopher C; Faucher-Giguère, Claude-André; Schreiber, Corentin; Ma, Xiangcheng; Hopkins, Philip F; Quataert, Eliot (October 2019, Monthly Notices of the Royal Astronomical Society)

   Abstract Dust temperature is an important property of the interstellar medium (ISM) of galaxies. It is required when converting (sub)millimetre broad-band flux to total infrared luminosity (LIR), and hence star formation rate, in high-redshift galaxies. However, different definitions of dust temperatures have been used in the literature, leading to different physical interpretations of how ISM conditions change with, e.g. redshift and star formation rate. In this paper, we analyse the dust temperatures of massive ($$M_{\rm star} \gt 10^{10}\, \mathrm{M}_{\odot }$$) $$z$$ = 2–6 galaxies with the help of high-resolution cosmological simulations from the Feedback in Realistic Environments (fire) project. At $$z$$ ∼ 2, our simulations successfully predict dust temperatures in good agreement with observations. We find that dust temperatures based on the peak emission wavelength increase with redshift, in line with the higher star formation activity at higher redshift, and are strongly correlated with the specific star formation rate. In contrast, the mass-weighted dust temperature, which is required to accurately estimate the total dust mass, does not strongly evolve with redshift over $$z$$ = 2–6 at fixed IR luminosity but is tightly correlated with LIR at fixed $$z$$. We also analyse an ‘equivalent’ dust temperature for converting (sub)millimetre flux density to total IR luminosity, and provide a fitting formula as a function of redshift and dust-to-metal ratio. We find that galaxies of higher equivalent (or higher peak) dust temperature (‘warmer dust’) do not necessarily have higher mass-weighted temperatures. A ‘two-phase’ picture for interstellar dust can explain the different scaling relations of the various dust temperatures. 

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2. Damped Lyα Absorbers in Star-forming Galaxies at z < 0.15 Detected with the Hubble Space Telescope and Implications for Galactic Evolution

   https://doi.org/10.3847/1538-4357/ac5fab  

   Kulkarni, Varsha P.; Bowen, David V.; Straka, Lorrie A.; York, Donald G.; Gupta, Neeraj; Noterdaeme, Pasquier; Srianand, Raghunathan (April 2022, The Astrophysical Journal)

   Abstract We report Hubble Space Telescope Cosmic Origins Spectrograph spectroscopy of 10 quasars with foreground star-forming galaxies at 0.02 < z < 0.14 within impact parameters of ∼1–7 kpc. We detect damped/sub-damped Ly α (DLA/sub-DLA) absorption in 100% of cases where no higher-redshift Lyman-limit systems extinguish the flux at the expected wavelength of Ly α absorption, obtaining the largest targeted sample of DLA/sub-DLAs in low-redshift galaxies. We present absorption measurements of neutral hydrogen and metals. Additionally, we present Green Bank Telescope 21 cm emission measurements for five of the galaxies (including two detections). Combining our sample with the literature, we construct a sample of 117 galaxies associated with DLA/sub-DLAs spanning 0 < z < 4.4, and examine trends between gas and stellar properties, and with redshift. The H i column density is anticorrelated with impact parameter and stellar mass. More massive galaxies appear to have gas-rich regions out to larger distances. The specific star formation rate (sSFR) of absorbing galaxies increases with redshift and decreases with M *, consistent with evolution of the star formation main sequence (SFMS). However, ∼20% of absorbing galaxies lie below the SFMS, indicating that some DLA/sub-DLAs trace galaxies with longer-than-typical gas-depletion timescales. Most DLA/sub-DLA galaxies with 21 cm emission have higher H i masses than typical galaxies with comparable M *. High M HI / M * ratios and high sSFRs in DLA/sub-DLA galaxies with M * < 10 9 M ⊙ suggest these galaxies may be gas-rich because of recent gas accretion rather than inefficient star formation. Our study demonstrates the power of absorption and emission studies of DLA/sub-DLA galaxies for extending galactic evolution studies to previously under-explored regimes of low M * and low SFR. 

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3. Metals and a search for molecules in the distant Universe: Magellan mike observations of sub-DLAs at 2 < z < 3

   https://doi.org/10.1093/mnras/stab926  

   Poudel, Suraj; Kulkarni, Varsha P; Som, Debopam; Péroux, Céline (April 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT We present abundance measurements of the elements Zn, S, O, C, Si, and Fe for four sub-DLAs at redshifts ranging from z = 2.173 to 2.635 using observations from the MIKE spectrograph on the Magellan telescope to constrain the chemical enrichment and star formation of gas-rich galaxies. Using weakly depleted elements O, S, and or Zn, we find the metallicities after the photoionization corrections to be [S/H] = −0.50 ± 0.11, [O/H] > −0.84, [O/H] = −1.27 ± 0.12, and [Zn/H]  = +0.40 ± 0.12 for the absorbers at z  = 2.173, 2.236, 2.539, and 2.635, respectively. Moreover, we are able to put constraints on the electron densities using the fine structure lines of C ii⋆ and Si ii⋆ for two of the sub-DLAs. We find that these values are much higher than the median values found in DLAs in the literature. Furthermore, we estimate the cooling rate lc = 1.20 × 10−26 erg s−1 per H atom for an absorber at z = 2.173, suggesting higher star formation rate density in this sub-DLA than the typical star formation rate density for DLAs at similar redshifts. We also study the metallicity versus velocity dispersion relation for our absorbers. Most of the absorbers follow the trend one can expect from the mass versus metallicity relation for sub-DLAs in the literature. Finally, we are able to put limits on the molecular column density from the non-detections of various strong lines of CO molecules. We estimate 3σ upper limits of logN(CO, J = 0) < 13.87, logN(CO, J = 0) < 13.17, and logN(CO, J = 0) < 13.08, respectively, from the non-detections of absorption from the J = 0 level in the CO AX 0–0, 1–0, and 2–0 bands near 1544, 1510, and 1478 Å. 

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4. Metal Lines Associated with the Lyα Forest from eBOSS Data

   https://doi.org/10.3847/1538-4357/ac7b2e  

   Yang, Li; Zheng, Zheng; du Mas des Bourboux, Hélion; Dawson, Kyle; Pieri, Matthew M.; Rossi, Graziano; Schneider, Donald P.; Macorra, Axel de; Gutiérrez, Adrean Muñoz (August 2022, The Astrophysical Journal)

   Abstract We investigate the metal species associated with the Ly α forest in eBOSS quasar spectra. Metal absorption lines are revealed in stacked spectra from cross-correlating the selected Ly α absorbers in the forest and the flux fluctuation field. Up to 13 metal species are identified as being associated with relatively strong Ly α absorbers (those with flux fluctuations − 1.0 < δ Ly α < − 0.6 and with a neutral hydrogen column density of ∼ 10 15−16 cm −2 ) over the absorber redshift range of 2 < z abs < 4. The column densities of these species decrease toward higher redshift and for weaker Ly α absorbers. From modeling the column densities of various species, we find that the column density pattern suggests contributions from multiple gas components, both in the circumgalactic medium (CGM) and the intergalactic medium (IGM). While the low-ionization species (e.g., C ii , Si ii , and Mg ii ) can be explained by high-density, cool gas ( T ∼ 10 4 K) from the CGM, the high-ionization species may reside in low-density or high-temperature gas in the IGM. The measurements provide inputs for modeling the metal contamination in the Ly α forest baryon acoustic oscillation measurements. Comparisons with metal absorptions in high-resolution quasar spectra and hydrodynamic galaxy formation simulations can further elucidate the physical conditions of these Ly α absorbers. 

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5. Characterizing Extreme Emission Line Galaxies. II. A Self-consistent Model of Their Ionizing Spectrum*

   https://doi.org/10.3847/1538-4357/ac8f2c  

   Olivier, Grace M.; Berg, Danielle A.; Chisholm, John; Erb, Dawn K.; Pogge, Richard W.; Skillman, Evan D. (October 2022, The Astrophysical Journal)

   Abstract Observations of high-redshift galaxies ( z > 5) have shown that these galaxies have extreme emission lines with equivalent widths much larger than their local star-forming counterparts. Extreme emission line galaxies (EELGs) in the nearby universe are likely analogs to galaxies during the Epoch of Reionization and provide nearby laboratories to understand the physical processes important to the early universe. We use Hubble Space Telescope/Cosmic Origins Spectrograph and Large Binocular Telescope/Multi-Object Double Spectrographs spectra to study two nearby EELGs, J104457 and J141851. The far-UV spectra indicate that these two galaxies contain stellar populations with ages ≲10 Myr and metallicities ≤0.15 Z ⊙ . We use photoionization modeling to compare emission lines from models of single-age bursts of star formation to observed emission lines and find that the single-age bursts do not reproduce high-ionization lines including [O iii ] or very-high-ionization lines like He ii or O iv ]. Photoionization modeling using the stellar populations fit from the UV continuum similarly is not capable of reproducing the very-high-energy emission lines. We add a blackbody to the stellar populations fit from the UV continuum to model the necessary high-energy photons to reproduce the very-high-ionization lines of He ii and O iv ]. We find that we need a blackbody of 80,000 K and ∼45%–55% of the luminosity from the blackbody and young stellar population to reproduce the very-high-ionization lines while simultaneously reproducing the low-, intermediate-, and high-ionization emission lines. Our self-consistent model of the ionizing spectra of two nearby EELGs indicates the presence of a previously unaccounted-for source of hard ionizing photons in reionization analogs. 

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