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

We show how the ratio of the abundances of Ar, Si and Fe as derived from FUSE absorption spectra of I Zw 18 are aected by large-scale stochastic velocity elds (mesoturbulence). 21-cm observations with high spatial resolution show the presence of velocity elds with large correlation lengths. FUSE observations were performed with a large entrance aperture which fully covered the galaxy. This means that the observed proles 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 (-chain/Fe) being similar to those derived from Galactic metal-poor stars. Using a mesoturbulent approach, we found that the observed proles can be reproduced well with (Fe/H) = 2:4 0:1, and (Si, Ar/Fe) =0 :7 0:1.