Supersolar Metallicity in Weak Mg ii Absorption Systems at z ∼ 1.71

Abstract

Through photoionization modeling, constraints on the physical conditions of three z~1.7 single-cloud weak Mg II systems [Wr(2796) <1 weak Mg II absorbers, these are the first high metallicities derived for such systems at higher redshifts. (4) Two of the three weak Mg II systems also need additional low-metallicity, broad Lyα absorption lines, offset in velocity from the metal-line absorption, in order to reproduce the full Lyα profile. (5) Metallicities in single-cloud weak Mg II systems are more than an order of magnitude larger than those in DLA systems at z~1.7. In fact, there appears to be a gradual decrease in metallicity with increasing NHI, from these, the most metal-rich Lyα forest clouds, to Lyman limit systems, to sub-DLAs, and finally to the DLAs. Based on archive data of observations made with the ESO Telescopes at the La Silla or Paranal Observatories under programs, 65.O-0411, 66.A-0221, and 67.A-0280.