Argon, silicon and iron abundances in the damped Ly-α system I Zw 18

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

Corresponding author: S. A. Levshakov, sergei@oat.ts.astro.it

Received: 28 November 2000
Accepted: 1 May 2001

Abstract

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 [ α-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] , and [Si, Ar/Fe] .