Discovery of Damped Lyman-Alpha Systems at Redshifts Less Than 1.65 and Results on their Incidence and Cosmological Mass Density

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  • 10 September 1999
Abstract
We report results on the incidence and cosmological mass density of damped Lyman-alpha (DLA) systems at redshifts less that 1.65. We used HST and an efficient non-traditional (but unbiased) survey technique to discover DLA systems at redshifts z0.6A. (2) The incidence of DLA systems per unit redshift, n(DLA), is observed to decrease with decreasing redshift. (3) On the other hand, the cosmological mass density of neutral gas in low-redshift DLA absorbers, Omega(DLA), is observed to be comparable to that observed at high redshift. (4) The low-redshift DLA absorbers exhibit a significantly larger fraction of very high column density systems in comparison to determinations at both high redshift and locally.

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