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

Sub-damped Lyman alpha systems (subDLAs; H I column densities of 19.0 = 18.9. We compared the implications of searching for subDLAs solely using H 1 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 Hi mass density (Omega(HI)) of subDLAs and compared with our previous work based on the XQ-100 damped Lyman 0, systems. We do not find any significant redshift evolution in f(N, X) or Omega(HI) for subDLAs. However, subDLAs contribute 10-20 per cent of the total Omega(HI) measured at redshifts 2 < z < 5, and thus have a small but significant contribution to the HI budget of the Universe.© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
SL was partially funded by UCh/VID project ENL18/18.