OBSERVATIONS OF NICKEL, CHROMIUM, AND ZINC IN QSO ABSORPTION-LINE SYSTEMS

We present new observations of Ni II, Cr II, and Zn II in several damped Lya QSO absorption-line systems at z ≈ 2. Using the N(Zn II)/N(H I) ratio as a probe of the metallicity and N(Cr II)/N(Zn II) as a measure of the dust content, we find that the heavy-element abundances in the z = 1.921 system toward the QSO 2206 - 199N are 20% solar and that the dust-to-gas ratio is 11% of the Galactic disk value. Our observations of these species in the z = 2.309 system toward PHL 957 yield a more extreme metallicity (4% solar) and dust-to-gas ratio (3% Galactic). We also find a depletion of Ni in the z = 2.039 absorber toward PKS 0458-020 and an absence of C I absorption in the z ≈ 2 damped systems toward 1215 + 333 and 2359-022 which are consistent with a lack of dust. Among the four damped systems whose Ni, Cr, and Zn abundances have been examined quantitatively to date, all show convincing evidence of much lower metallicities and dust content than the Galactic disk. We discuss the implications of these results with regard to the interpretation of the high-redshift damped Lyα systems as an evolving population of young galaxies.