Relative abundance pattern along the profile of high redshift damped Lyman-alpha systems

Abstract

We investigate abundance ratios along the profiles of six high-redshift Damped Lyman-α systems, three of them beeing associated with H2 absorption. We use a new method to derive optical depths in each velocity pixel. The variations of the pixel abundance ratios are found to be remarquably small and usually smaller than a factor of two within a profile. This results holds when considering independent sub-clumps in the same system. Only in the components where H2 is detected is the depletion factor significantly enhanced. There is a strong correlation between [Fe/S] and [Si/S] ratios showing that the abundance ratio patterns are definitely related to the presence of dust. The depletion pattern is usually close to that seen in warm halo gas of our Galaxy.