Sub-damped Lyman α systems in the XQ-100 survey I - Identification and contribution to the cosmological HI budget

DOI: 
10.1093/mnras/stz2012
Publication date: 
01/07/2019
Main author: 
Berg, Trystyn A. M.
IAA authors: 
Sánchez-Ramírez, Rubén
Authors: 
Berg, Trystyn A. M.;Ellison, Sara L.;Sánchez-Ramírez, Rubén;López, Sebastián;D'Odorico, Valentina;Becker, George D.;Christensen, Lise;Cupani, Guido;Denney, Kelly D.;Worseck, Gábor
Journal: 
Monthly Notices of the Royal Astronomical Society
Refereed: 
Yes
Publication type: 
Article
Pages: 
4356-4369
Abstract: 
Sub-damped Lyman α systems (subDLAs; H I column densities of 19.0 ≤ logN(H I) &lt;20.3) are rarely included in the cosmic H I census performed at redshifts z<SUB>abs</SUB> ≳ 1.5, yet are expected to contribute significantly to the overall H I mass budget of the Universe. In this paper, we present a blindly selected sample of 155 subDLAs found along 100 quasar sightlines (with a redshift path length ∆X = 475) in the XQ-100 legacy survey to investigate the contribution of subDLAs to the H I mass density of the Universe. The impact of X-Shooter's spectral resolution on Lyα absorber identification is evaluated, and found to be sufficient for reliably finding absorbers down to a column density of logN(H I)≥18.9. We compared the implications of searching for subDLAs solely using H I absorption versus the use of metal lines to confirm the identification, and found that metal-selection techniques would have missed 75 subDLAs. Using a bootstrap-Monte Carlo simulation, we computed the column density distribution function (f(N, X)) and the cosmological H I mass density (Ω _{H I}) of subDLAs and compared with our previous work based on the XQ-100 damped Lyman α systems. We do not find any significant redshift evolution in f(N, X) or Ω _{H I} for subDLAs. However, subDLAs contribute 10-20 per cent of the total Ω _{H I} measured at redshifts 2 &lt; z &lt; 5, and thus have a small but significant contribution to the H I budget of the Universe.
Database: 
ADS
SCOPUS
URL: 
https://www.scopus.com/inward/record.uri?eid=2-s2.0-85082594154&doi=10.1093%2fmnras%2fstz2012&partnerID=40&md5=cdbd914b4efc24e41e84f3d68a14450b
ADS Bibcode: 
2019MNRAS.488.4356B
Keywords: 
galaxies: high redshift;galaxies: ISM;quasars: absorption lines;Astrophysics - Astrophysics of Galaxies