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

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 (DESI) and the WHT Enhanced Area Velocity Explorer (WEAVE) surveys, finding >90% completeness and purity for N(HI)> 10^17.2 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 N(HI)>10^17.5 cm^-2 between z~3.1-4.0 with a completeness and purity of >90% for the classification of LLSs. Using this sample, we measure a number of LLSs per unit redshift of 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 HI column densities, and for the identification of broad absorption line quasars.

12 pages, 13 figures. MNRAS in press. The classification of the full dataset is available as supplementary data at MNARS online

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Cited by in corpus (7)

• The wide-field, multiplexed, spectroscopic facility WEAVE: Survey design, overview, and simulated implementation
• MUSE Analysis of Gas around Galaxies (MAGG) -- IV: The gaseous environment of $z\sim$ 3-4 Lyman-alpha emitting galaxies
• The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: The Damped Lyman-$\alpha$ systems Catalog
• Constraining the cosmic UV background at z>3 with MUSE Lyman-α emission observations
• Metal Lines Associated with the Lyman-alpha Forest from eBOSS Data
• Probing the physical properties of the intergalactic medium using gamma-ray bursts
• Probing the physical properties of the intergalactic medium using blazars