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Sub-damped Lyman α systems in the XQ-100 survey – II. Chemical evolution at 2.4 ≤ z ≤ 4.3

Berg, Trystyn AM; Fumagalli, Michele; D’Odorico, Valentina; Ellison, Sara L; López, Sebastián; Becker, George D; Christensen, Lise; Cupani, Guido; Denney, Kelly D; Sánchez-Ramírez, Rubén; Worseck, Gábor

Sub-damped Lyman α systems in the XQ-100 survey – II. Chemical evolution at 2.4 ≤ z ≤ 4.3 Thumbnail


Trystyn AM Berg

Valentina D’Odorico

Sara L Ellison

Sebastián López

George D Becker

Lise Christensen

Guido Cupani

Kelly D Denney

Rubén Sánchez-Ramírez

Gábor Worseck


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.


Berg, T. A., Fumagalli, M., D’Odorico, V., Ellison, S. L., López, S., Becker, G. D., …Worseck, G. (2021). Sub-damped Lyman α systems in the XQ-100 survey – II. Chemical evolution at 2.4 ≤ z ≤ 4.3. Monthly Notices of the Royal Astronomical Society, 502(3), 4009-4025.

Journal Article Type Article
Acceptance Date Jan 18, 2021
Online Publication Date Jan 22, 2021
Publication Date 2021-04
Deposit Date Sep 21, 2021
Publicly Available Date Sep 21, 2021
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 502
Issue 3
Pages 4009-4025


Published Journal Article (1.3 Mb)

Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2021 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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