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

¹ Institut d'Astrophysique de Paris, UMR 7095, 98 bis boulevard Arago, 75014 Paris, France e-mail: rodrig@iap.fr
² Observatoire de Paris, LERMA, UMR 8112, 61 avenue de l'Observatoire, 75014 Paris, France
³ Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003-9305, USA
⁴ European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Vitacura, Santiago, Chile
⁵ IUCAA, Post Bag 4, Ganesh Khind, Pune 411 007, India

Received: 8 December 2004
Accepted: 23 August 2005

Abstract

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