Sub-damped Lyman α systems in the XQ-100 survey - II. Chemical evolution at 2.4 ≤ z ≤ 4.3
Date Issued
2021
Author(s)
Berg, Trystyn A. M.
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Ellison, Sara L.
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López, Sebastián
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Becker, George D.
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Christensen, Lise
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Denney, Kelly D.
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Worseck, Gábor
Abstract
We present the measured gas-phase metal column densities in 155 sub-damped Ly α systems (subDLAs) with the aim to investigate the contribution of subDLAs to the chemical evolution of the Universe. The sample was identified within the absorber-blind XQ-100 quasar spectroscopic survey over the redshift range 2.4 ≤ zabs ≤ 4.3. Using all available column densities of the ionic species investigated (mainly C IV, Si II, Mg II, Si IV, Al II, Fe II, C II, and O I; in order of decreasing detection frequency), we estimate the ionization-corrected gas-phase metallicity of each system using Markov chain Monte Carlo techniques to explore a large grid of CLOUDY ionization models. Without accounting for ionization and dust depletion effects, we find that the H I-weighted gas-phase metallicity evolution of subDLAs is consistent with damped Ly α systems (DLAs). When ionization corrections are included, subDLAs are systematically more metal poor than DLAs (between ≍0.5σ and ≍3σ significance) by up to ≍1.0 dex over the redshift range 3 ≤ zabs ≤ 4.3. The correlation of gas phase [Si/Fe] with metallicity in subDLAs appears to be consistent with that of DLAs, suggesting that the two classes of absorbers have a similar relative dust depletion pattern. As previously seen for Lyman limit systems, the gas phase [C/O] in subDLAs remains constantly solar for all metallicities indicating that both subDLAs and Lyman limit systems could trace carbon-rich ejecta, potentially in circumgalactic environments.
Volume
502
Issue
3
Start page
4009
Issn Identifier
0035-8711
Ads BibCode
2021MNRAS.502.4009B
Rights
open.access
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