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

Sandhya M. Rao·David A. Turnshek
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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 z<1.65, where we observe the Lyman-alpha line in known MgII absorption-line systems. We uncovered 14 DLA lines including 2 serendipitously. We find that (1) The DLA absorbers are drawn almost exclusively from the population of MgII absorbers which have rest equivalent widths W(2796)>0.6A. (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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Sandhya M. Rao, David A. Turnshek. 2000-05-02. Discovery of Damped Lyman-Alpha Systems at Redshifts Less Than 1.65 and Results on their Incidence and Cosmological Mass Density. https://doi.org/10.1086/317344

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