The Cosmic Ultraviolet Baryon Survey (CUBS) – III. Physical properties and elemental abundances of Lyman-limit systems at z < 1

Journal Article · 22 June 2021 · Monthly Notices of the Royal Astronomical Society

DOI: https://doi.org/10.1093/mnras/stab1661 · OSTI ID:1807604

Zahedy, Fakhri S. ; Chen, Hsiao-Wen ; Cooper, Thomas M.; Boettcher, Erin; Johnson, Sean D. ; Rudie, Gwen C.; Chen, Mandy C.; Cantalupo, Sebastiano; Cooksey, Kathy L.; Faucher-Giguère, Claude-André ; Greene, Jenny E.; Lopez, Sebastian ; Mulchaey, John S.; Penton, Steven V.; Petitjean, Patrick; Putman, Mary E.; Rafelski, Marc; Rauch, Michael; Schaye, Joop ; Simcoe, Robert A. ; Walth, Gregory L.

ABSTRACT We present a systematic investigation of physical conditions and elemental abundances in four optically thick Lyman-limit systems (LLSs) at z = 0.36–0.6 discovered within the Cosmic Ultraviolet Baryon Survey (CUBS). Because intervening LLSs at z < 1 suppress far-UV (ultraviolet) light from background QSOs, an unbiased search of these absorbers requires a near-UV-selected QSO sample, as achieved by CUBS. CUBS LLSs exhibit multicomponent kinematic structure and a complex mix of multiphase gas, with associated metal transitions from multiple ionization states such as C ii, C iii, N iii, Mg ii, Si ii, Si iii, O ii, O iii, O vi, and Fe ii absorption that span several hundred km s−1 in line-of-sight velocity. Specifically, higher column density components (log N(H i)/cm−2≳ 16) in all four absorbers comprise dynamically cool gas with $$\langle T \rangle =(2\pm 1) \times 10^4\,$$K and modest non-thermal broadening of $$\langle b_\mathrm{nt} \rangle =5\pm 3\,$$km s−1. The high quality of the QSO absorption spectra allows us to infer the physical conditions of the gas, using a detailed ionization modelling that takes into account the resolved component structures of H i and metal transitions. The range of inferred gas densities indicates that these absorbers consist of spatially compact clouds with a median line-of-sight thickness of $$160^{+140}_{-50}$$ pc. While obtaining robust metallicity constraints for the low density, highly ionized phase remains challenging due to the uncertain $$N\mathrm{(H\, {\small I})}$$, we demonstrate that the cool-phase gas in LLSs has a median metallicity of $$\mathrm{[\alpha /H]_{1/2}}=-0.7^{+0.1}_{-0.2}$$, with a 16–84 percentile range of [α/H] = (−1.3, −0.1). Furthermore, the wide range of inferred elemental abundance ratios ([C/α], [N/α], and [Fe/α]) indicate a diversity of chemical enrichment histories. Combining the absorption data with deep galaxy survey data characterizing the galaxy environment of these absorbers, we discuss the physical connection between star-forming regions in galaxies and diffuse gas associated with optically thick absorption systems in the z < 1 circumgalactic medium.

• Sponsoring Organization: USDOE
• OSTI ID: 1807604
• Journal Information: Monthly Notices of the Royal Astronomical Society, Journal Name: Monthly Notices of the Royal Astronomical Society Journal Issue: 1 Vol. 506; ISSN 0035-8711
• Publisher: Oxford University PressCopyright Statement
• Country of Publication: United Kingdom
• Language: English