Neutral-Gas-Phase Metal Abundances in ZnII-Selected Quasar Absorption Line Systems near Redshift \(z=1.2\)

We present ten metallicity measurements for quasar absorbers near \(z=1.2\) that were selected for having unusually significant ZnII absorption in their SDSS spectra. Follow-up UV space spectroscopy of the Ly\(\alpha\) region shows that all ten have damped Ly\(\alpha\) (DLA) absorption, corresponding to neutral hydrogen column densities in the range \(2.4\times 10^{20}\) \(\le\) N(HI) \(\le\) \(2.5\times 10^{21}\) atoms cm\(^{-2}\), and indicating that the gas is very optically thick and essentially neutral. The sample is a very small subset of systems compiled by searching the University of Pittsburgh catalog of \(\approx 30,000\) intervening MgII absorption line systems in SDSS quasar spectra up to DR7. We started by isolating \(\approx 3,000\) that had strong MgII absorption in the redshift interval \(1.0 < z < 1.5\) in brighter background quasars. Of these, 36 exhibited significant absorption near ZnII. Space UV spectroscopy was then obtained for nine of these (25% of the total), and a tenth system in a fainter quasar was found in the HST archives. The result is a representative sample of the highest Zn\(^+\) columns of gas within the DLA population. These ZnII-selected systems define the upper envelope of DLA metallicities near \(z=1.2\). They show a tight anti-correlation between N(HI) and [Zn/H], with the higher metallicity systems clearly exhibiting more depletion based on [Cr/Zn] values. The various metal-line measurements (Zn, Cr, Si, Fe, Mn) indicate evolved neutral gas with \(-0.9 \le\) [Zn/H] \(\le +0.4\).