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Astron. Astrophys. 321, 45-54 (1997)


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Chemical evolution of damped Ly [FORMULA] systems

F. Matteucci 1, P. Molaro 2 and G. Vladilo 2

1 Dipartimento di Astronomia, Università di Trieste, SISSA, Via Beirut 2-4, I-34013 Trieste, Italy
2 Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, I-34131 Trieste, Italy

Received 19 January 1996 / Accepted 21 May 1996

Abstract

High redshift DLA systems suggest that the relative abundances of elements might be roughly solar, although with absolute abundances of more than two orders of magnitude below solar. The result comes from observations of the [SII/ZnII] ratio, which is a reliable diagnostic of the true abundance, and from DLA absorbers with small dust depletion and negligible HII contamination. In particular, in two DLA systems nitrogen is detected and at remarkably high levels (Vladilo et al. 1995, Molaro et al. 1996, Green et al. 1995, Kulkarni et al. 1996). Here we compare the predictions from chemical evolution models of galaxies of different morphological type with the abundances and abundance ratios derived for such systems. We conclude that solar ratios and relatively high nitrogen abundances can be obtained in the framework of a chemical evolution model assuming short but intense bursts of star formation, which in turn trigger enriched galactic winds, and a primary origin for nitrogen in massive stars. Such a model is the most successful in describing the chemical abundances of dwarf irregular galaxies and in particular of the peculiar galaxy IZw18. Thus, solar ratios at very low absolute abundances, if confirmed, seem to favour dwarf galaxies rather than spirals as the progenitors of at least some of the DLA systems.

Key words: galaxies: abundances – galaxies: evolution – Galaxy: halo – cosmology: observations

Send offprint requests to: F. Matteucci, Dipartimento di Astronomia, Università di Trieste, SISSA, Via Beirut 2-4, I-34013 Trieste, Italy

© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998

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