Astron. Astrophys. 327, 22-26 (1997)

Zinc and chromium abundances
in a third damped Lyman  system at intermediate redshift

Max Pettini ¹ and David V. Bowen <sup>2

1</sup> Royal Greenwich Observatory, Madingley Road, Cambridge, CB3 0EZ, UK
² Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK

Received 21 April 1997 / Accepted 23 May 1997

Abstract

We have determined the metallicity of the damped Lyman  system in the bright QSO EX 0302223; this is only the third such measurement at redshifts . Unlike the previous two cases, we find that the abundance of Zn is only a factor of lower than in the Galactic interstellar medium today and is entirely compatible with the typical metallicity of stars in the Milky Way disk at a look-back time of 9.5 Gyrs. Although the galaxy responsible for producing the absorption system has yet to be positively identified, our observations show that galaxies on a chemical evolution path similar to that of the Milky Way do contribute to the damped Lyman  population at intermediate redshifts. Cr is 2.5 times less abundant than Zn, presumably because of depletion onto dust; however, the degree of depletion is less severe than in diffuse interstellar clouds in the disk of our Galaxy and in the Magellanic Clouds. Evidently, the interstellar environment in damped Lyman  galaxies is less conducive to the formation and survival of dust grains (and molecular hydrogen), but the physical processes at the root of this effect have yet to be clarified.

Key words: galaxies: abundances - galaxies: ISM - quasar: absorption lines - quasar: individual: EX 0302-223

SIMBAD Objects

Contents

• 1. Introduction
• 2. The DLA absorber in EX 0302223
• 3. Zn and Cr abundances
• 4. Discussion
  • 4.1. Chemical evolution
  • 4.2. Dust depletion of chromium
• Acknowledgements
• References

This article was processed by the author using Springer-Verlag TEX A&A macro package version 3.

© European Southern Observatory (ESO) 1997

Online publication: April 8, 1998
helpdesk.link@springer.de