Damped Lyα gas metallicities at redshifts z=0.9-2.0 from Sloan Digital Sky Survey spectra

Using Sloan Digital Sky Survey early data release spectra, we have identified 370 Mg II absorption systems with Mg II lambda2796 rest equivalent widths greater than or equal to 1 Angstrom and redshifts z = 0.9-2.2. From our previous and ongoing Hubble Space Telescope UV spectroscopic studies, we estimate that the mean neutral hydrogen column density of a system selected in this manner is N-HI = (3.6 +/- 1.3) x 10(20) atoms cm(-2), which corresponds to the damped Lyalpha ( DLA) regime. We have formed high signal- to- noise ratio composite spectra using 223 of these systems with z = 0.9-2.0 in order to study the strength of the Zn II and Cr II absorption lines corresponding to this mean neutral hydrogen column density. After making a correction for missed DLAs, overall we find that [Zn/H] = -1.13 +/- 0.19. We find [Cr/Zn] = -.45 +/- 0.13, which indicates that approximate to 65% of the Cr is depleted onto grains, but this does not correct for the missed DLAs. We have also derived Zn and Cr abundances in two kinematic regimes, and within each regime we consider two redshift intervals. We find trends that indicate that metallicities are higher in the composites in which the absorption has larger velocity spreads as measured by Mg II lambda2796 rest equivalent width. Larger velocity spreads may correspond to deeper gravitational potential wells that represent more massive and chemically evolved structures and/or regions associated with winds from starbursting galaxies, also leading to kinematically broad structures of chemically enriched gas. Within the large velocity spread regime, we find that at lower redshifts the Zn metallicity is larger and more Cr is depleted onto grains.