The statistical properties of neutral gas at z < 1.65 from UV measurements of Damped Lyman Alpha systems
Abstract
We derive the statistical properties of neutral gas at redshifts 0.11 < z < 1.65 from ultraviolet (UV) measurements of quasar Ly α absorption lines corresponding to 369 Mg II systems with W^{λ 2796}_{0} ≥ 0.3 Å. In addition to the 41 damped Lyman alpha (DLA) systems presented in Rao et al. (2006), the current DLA sample includes 29 newly discovered DLAs. Formally, this DLA sample includes 70 systems with N_{H I}≥ 2× 10^{20} atoms cm^{2}. We find that the incidence of DLAs, or the product of their gas crosssection and their comoving number density, can be described by n_{DLA}(z) = (0.027 ± 0.007)(1 + z)^{(1.682 ± 0.200)} over the redshift range of 0 < z < 5. The cosmic mass density of neutral gas can be described by Ω_{DLA}(z) = (4.77 ± 1.60) × 10^{4}(1 + z)^{(0.64 ± 0.27)}. The lowredshift column density distribution function is well fitted by a power law of the form f (N) ∼ N^{β} with β = 1.46 ± 0.20. It is consistent with the high redshift as well as z = 0 estimates at the highcolumn density end but lies between them at the lowcolumn density end. We discuss possible N_{H I} and metallicity bias in Mg IIselected DLA samples and show that such biases do not exist in the current data at z < 1.65. Thus, at least at z < 1.65, DLAs found through Mg II selection statistically represent the true population of DLAs. However, we caution that studies of DLA metallicities should take into account the relative incidence of DLAs with respect to W_0^{λ 2796} (or gas velocity spread) in order to correctly measure the mean neutralgas cosmic metallicity of the Universe.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 November 2017
 DOI:
 10.1093/mnras/stx1787
 arXiv:
 arXiv:1704.01634
 Bibcode:
 2017MNRAS.471.3428R
 Keywords:

 galaxies: evolution;
 galaxies: formation;
 galaxies: ISM;
 quasars: absorption lines;
 Astrophysics  Astrophysics of Galaxies
 EPrint:
 16 pages