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Astron. Astrophys. 363, 69-83 (2000)


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Damped Lyman [FORMULA] systems at z = 0.68 and z = 1.15 towards HE 1122-1649 and HE 0515-4414 *

A. de la Varga 1, D. Reimers 1, D. Tytler 2, T. Barlow 3 and S. Burles 4

1 Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
2 Center for Astrophysics and Space Sciences, University of California, San Diego, MS-0424, La Jolla, CA 92093-0424, USA
3 California Institute of Technology, 100-22, Pasadena, CA 91125, USA
4 Department of Astronomy and Astrophysics, University of Chicago, 5640 S. Ellis Ave., Chicago, IL 60637, USA

Received 23 December 1998 / Accepted 3 August 2000

Abstract

Detailed analysis of the spectral lines from two low redshift damped Lyman alpha absorbers (DLA) confirms that they are a heterogeneous population. Both systems have low metal abundances of approximately 0.05 to 0.1 solar. The abundance pattern of the DLA at [FORMULA] towards HE 0515-4414 shows dust depletion comparable to that found in our Galaxy, while the system at [FORMULA] towards HE 1122-1649 shows abundance ratios resembling metal-poor halo stars with no dust depletion, for a comparable H I column. Constraints for N/Fe and N/Si also hint at [FORMULA] DLA as a galaxy with recent star formation. The trend of increasing C I /H I with decreasing z is discussed. Only weak absorption from highly-ionized species associated with the DLA at moderate z have been detected and it probably originates in regions distinct from the low ionization gas. The low-ion profiles show very complex structures and are too large to be explained by the rotation of a disk: the system at [FORMULA] spans over [FORMULA] 300 km s-1  and the [FORMULA] DLA presents substructure over more than 700 km s-1 , the largest velocity extent found up to date for a DLA.

Key words: galaxies: quasars: absorption lines – galaxies: quasars: individual: HE 1122-1649, HE 0515-4414 – galaxies: abundances – galaxies: evolution – galaxies: ISM – cosmology: observations

* Based on observations performed at ESO/La Silla, on observations with the NASA/ESA Hubble Space Telescope and on observations at Keck Observatory.

Send offprint requests to: A. de la Varga (avarga@hs.uni-hamburg.de)

© European Southern Observatory (ESO) 2000

Online publication: December 5, 2000

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