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1. Sub-damped Lyman α systems in the XQ-100 survey – I. Identification and contribution to the cosmological H i budget

   https://doi.org/10.1093/mnras/stz2012  

   Berg, Trystyn A; Ellison, Sara L; Sánchez-Ramírez, Rubén; López, Sebastián; D’Odorico, Valentina; Becker, George D; Christensen, Lise; Cupani, Guido; Denney, Kelly D; Worseck, Gábor (September 2019, Monthly Notices of the Royal Astronomical Society)

   Abstract Sub-damped Lyman α systems (subDLAs; H i column densities of 19.0 ≤ logN(H i) < 20.3) are rarely included in the cosmic H i census performed at redshifts zabs ≳ 1.5, yet are expected to contribute significantly to the overall H i mass budget of the Universe. In this paper, we present a blindly selected sample of 155 subDLAs found along 100 quasar sightlines (with a redshift path-length ΔX = 475) in the XQ-100 legacy survey to investigate the contribution of subDLAs to the H i mass density of the Universe. The impact of X-Shooter’s spectral resolution on Ly α absorber identification is evaluated, and found to be sufficient for reliably finding absorbers down to a column density of logN(H i) ≥ 18.9. We compared the implications of searching for subDLAs solely using H i absorption versus the use of metal lines to confirm the identification, and found that metal-selection techniques would have missed 75 subDLAs. Using a bootstrap Monte Carlo simulation, we computed the column density distribution function (f(N, X)) and the cosmological H i mass density ($$\Omega _{\rm H\,{\small I}}$$) of subDLAs and compared with our previous work based on the XQ-100 damped Lyman α systems. We do not find any significant redshift evolution in f(N, X) or $$\Omega _{\rm H\,{\small I}}$$ for subDLAs. However, subDLAs contribute 10–20 per cent of the total $$\Omega _{\rm H\,{\small I}}$$ measured at redshifts 2 < z < 5, and thus have a small but significant contribution to the H i budget of the Universe. 

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2. On the Metallicities and Kinematics of the Circumgalactic Media of Damped Lyα Systems at z ∼ 2.5*

   https://doi.org/10.3847/1538-4357/acd34a  

   Urbano_Stawinski, Stephanie_M; Rubin, Kate_H_R; Prochaska, J_Xavier; Hennawi, Joseph_F; Tejos, Nicolas; Fumagalli, Michele; Rafelski, Marc; Kirby, Evan_N; Lusso, Elisabeta; Hafen, Zachary (July 2023, The Astrophysical Journal)

   Abstract We use medium- and high-resolution spectroscopy of close pairs of quasars to analyze the circumgalactic medium (CGM) surrounding 32 damped Lyαabsorption systems (DLAs). The primary quasar sightline in each pair probes an intervening DLA in the redshift range 1.6 <z_abs< 3.5, such that the secondary sightline probes absorption from Lyαand a large suite of metal-line transitions (including Oi, Cii, Civ, Siii, and Siiv) in the DLA host galaxy’s CGM at transverse distances 24 kpc ≤R_⊥≤ 284 kpc. Analysis of Lyαin the CGM sightlines shows an anticorrelation betweenR_⊥and Hicolumn density (N_HI) with 99.8% confidence, similar to that observed around luminous galaxies. The incidences of Ciiand SiiiwithN> 10¹³cm⁻²within 100 kpc of DLAs are larger by 2σthan those measured in the CGM of Lyman break galaxies (C_f(N_CII) > 0.89 and ${\mathrm{C}}_f\left(N_{\mathrm{Si}\mathrm{II}}\right)={0.75}_{-0.17}^{+0.12}$). Metallicity constraints derived from ionic ratios for nine CGM systems with negligible ionization corrections andN_HI> 10^18.5cm⁻²show a significant degree of scatter (with metallicities/limits across the range $-2.06\lesssim \log Z/Z_{\odot }\lesssim -0.75$), suggesting inhomogeneity in the metal distribution in these environments. Velocity widths of Civλ1548 and low-ionization metal species in the DLA versus CGM sightlines are strongly (>2σ) correlated, suggesting that they trace the potential well of the host halo overR_⊥≲ 300 kpc scales. At the same time, velocity centroids for Civλ1548 differ in DLA versus CGM sightlines by >100 km s⁻¹for ∼50% of velocity components, but few components have velocities that would exceed the escape velocity assuming dark matter host halos of ≥10¹²M_⊙. 

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3. 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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4. 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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5. METAL-Z: Measuring Dust Depletion in Low-metallicity Dwarf Galaxies

   https://doi.org/10.3847/1538-4357/ad307b  

   Hamanowicz, Aleksandra; Tchernyshyov, Kirill; Roman-Duval, Julia; Jenkins, Edward B; Rafelski, Marc; Gordon, Karl D; Zheng, Yong; Garcia, Miriam; Werk, Jessica (April 2024, The Astrophysical Journal)

   Abstract The cycling of metals between interstellar gas and dust is a critical aspect of the baryon cycle of galaxies, yet our understanding of this process is limited. This study focuses on understanding dust depletion effects in the low-metallicity regime (<20%Z_⊙) typical of cosmic noon. Using medium-resolution UV spectroscopy from the Cosmic Origins Spectrograph on board the Hubble Space Telescope, gas-phase abundances and depletions of iron and sulfur were derived toward 18 sight lines in local dwarf galaxies IC 1613 and Sextans A. The results show that the depletion of Fe and S is consistent with that found in the Milky Way (MW), LMC, and SMC. The depletion level of Fe increases with gas column density, indicating dust growth in the interstellar medium. The level of Fe depletion decreases with decreasing metallicity, resulting in the fraction of iron in gas ranging from 3% in the MW to 9% in IC 1613 and ∼19% in Sextans A. The dust-to-gas and dust-to-metal ratios (D/G,D/M) for these dwarf galaxies were estimated based on the MW relations between the depletion of Fe and other elements. The study finds thatD/Gdecreases only slightly sublinearly with metallicity, withD/Mdecreasing from 0.41 ± 0.05 in the MW to 0.11 ± 0.11 at 0.10Z_⊙(at logN(H) = 21 cm⁻²). The trend ofD/Gversus metallicity using depletion in local systems is similar to that inferred in Damped Lyαsystems from abundance ratios but lies higher than the trend inferred from far-IR measurements in nearby galaxies. 

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