SIMBAD references

We use the Hubble Space Telescope (HST) archive of ultraviolet (UV) quasar spectroscopy to conduct the first blind survey for damped Lyα absorbers (DLAs) at low redshift (z < 1.6). Our statistical sample includes 463 quasars with spectral coverage spanning a total redshift path Δz = 123.3 or an absorption path ΔX = 229.7. Within this survey path, we identify 4 DLAs defined as absorbers with H i column density N_HI ≥ 10^20.3/cm2, which implies an incidence per absorption length lDLA(X) = 0.017_–0.008^+0.014 at a median survey path redshift of z = 0.623. While our estimate of l_DLA(X) is lower than earlier estimates at z ≈ 0 from H i 21 cm emission studies, the results are consistent within the measurement uncertainties. Our data set is too small to properly sample the N_HI frequency distribution function f(N_HI, X), but the observed distribution agrees with previous estimates at z >2. Adopting the z > 2 shape of f(N_HI, X), we infer an H i mass density at z∼0.6 of ρ_HI^DLA = 0.25_–0.12^+0.20. This is significantly lower than previous estimates from targeted DLA surveys with the HST, but consistent with results from low-z H i 21 cm observations, and suggests that the neutral gas density of the universe has been decreasing over the past 10 Gyr.