Supersolar Super-Lyman Limit Systems

Abstract

We present abundance measurements for two super Lyman Limit systems (SLLS; quasar absorption line systems with 10^19 cm^-2 < N_HI < 10^20.3 cm^-2) selected from a set of metal-strong absorbers in the Sloan Digital Sky Survey quasar database. After applying estimate corrections for photoionization effects, we derive gas-phase metallicities of [M/H]=+0.7 +/- 0.2 dex for the SLLS at z=1.7749 toward SDSS0927+5621 and [M/H]=+0.05 +/- 0.1 dex for the SLLS at z=1.7678 toward SDSS0953+5230. The former exhibits among the highest gas metallicity of any astrophysical environment and its total metal surface density exceeds that of nearly every known damped Lya system. The properties of these absorbers -- high metallicity and large velocity width (> 300 km/s) -- resemble those of gas observed in absorption in the spectra of bright, star-forming galaxies at high redshift. We discuss the metal mass density of the SLLS based on these observations and our ongoing SLLS survey and argue that a conservative estimate to the total metal budget at z=2 is greater than 15% of the total, suggesting that the metal-rich LLS may represent the dominant metal reservoir in the young universe.