EDP Sciences
Free access
Volume 373, Number 3, July III 2001
Page(s) 836 - 842
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20010628

A&A 373, 836-842 (2001)
DOI: 10.1051/0004-6361:20010628

Argon, silicon and iron abundances in the damped Ly-$\alpha$ system I Zw 18

S. A. Levshakov1, W. H. Kegel2 and I. I. Agafonova1

1  Department of Theoretical Astrophysics, Ioffe Physico-Technical Institute, 194021 St. Petersburg, Russia
    e-mail: lev@astro.ioffe.rssi.ru
    e-mail: ira@astro.ioffe.rssi.ru
2  Insitut für Theoretische Physik der Universität Frankfurt am Main, 60054 Frankfurt/Main 11, Germany
    e-mail: kegel@astro.uni-frankfurt.de

(Received 28 November 2000 / Accepted 1 May 2001)

We show how the ratio of the abundances of Ar, Si and Fe as derived from FUSE absorption spectra of I Zw 18 are affected by large-scale stochastic velocity fields (mesoturbulence). 21-cm observations with high spatial resolution show the presence of velocity fields with large correlation lengths. FUSE observations were performed with a large entrance aperture which fully covered the galaxy. This means that the observed profiles are averaged over the full body of I Zw 18. Taking this into account, we show that the observations are consistent with the abundance ratios [ $\alpha$-chain/Fe] being similar to those derived from Galactic metal-poor stars. Using a mesoturbulent approach, we found that the observed profiles can be reproduced well with [Fe/H] $=-2.4\pm0.1$, and [Si, Ar/Fe] $= 0.7\pm0.1$.

Key words: line: formation -- line: profiles -- galaxies: individual: I Zw 18

Offprint request: S. A. Levshakov, sergei@oat.ts.astro.it

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