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Detecting neutral hydrogen at z ≳ 3 in large spectroscopic surveys of quasars

Fumagalli, Michele; Fotopoulou, Sotiria; Thomson, Laura

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Authors

Sotiria Fotopoulou

Laura Thomson



Abstract

We present a pipeline based on a random forest classifier for the identification of high column density clouds of neutral hydrogen (i.e. the Lyman limit systems, LLSs) in absorption within large spectroscopic surveys of z ≳ 3 quasars. We test the performance of this method on mock quasar spectra that reproduce the expected data quality of the Dark Energy Spectroscopic Instrument and the WHT (William Herschel Telescope) Enhanced Area Velocity Explorer surveys, finding ≳90 per cent completeness and purity for NHI≳1017.2 cm−2 LLSs against quasars of g < 23 mag at z ≈ 3.5–3.7. After training and applying our method on 10 000 quasar spectra at z ≈ 3.5–4.0 from the Sloan Digital Sky Survey (Data Release 16), we identify ≈6600 LLSs with NHI≳1017.5 cm−2 between z ≈ 3.1 and 4.0 with a completeness and purity of ≳90 per cent for the classification of LLSs. Using this sample, we measure a number of LLSs per unit redshift of ℓ(z) = 2.32 ± 0.08 at z = [3.3, 3.6]. We also present results on the performance of random forest for the measurement of the LLS redshifts and H I column densities, and for the identification of broad absorption line quasars.

Citation

Fumagalli, M., Fotopoulou, S., & Thomson, L. (2020). Detecting neutral hydrogen at z ≳ 3 in large spectroscopic surveys of quasars. Monthly Notices of the Royal Astronomical Society, 498(2), 1951-1962. https://doi.org/10.1093/mnras/staa2388

Journal Article Type Article
Acceptance Date Aug 7, 2020
Online Publication Date Aug 31, 2020
Publication Date 2020-10
Deposit Date Sep 1, 2020
Publicly Available Date Mar 28, 2024
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 498
Issue 2
Pages 1951-1962
DOI https://doi.org/10.1093/mnras/staa2388

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Copyright Statement
This article has been accepted for publication in Monthly notices of the Royal Astronomical Society. ©: 2020 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.





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