The Most Metal-Rich Intervening Quasar Absorber Known

The metallicity in portions of high-redshift galaxies has been successfully measured thanks to the gas observed in absorption in the spectra of quasars, in the Damped Lyman-α systems (DLAs). Surprisingly, the global mean metallicity derived from DLAs is about 1/10th solar at 0<∼z<∼4 leading to the so-called “missing-metals problem”. In this paper, we present high-resolution observations of a sub-DLA system at zabs=0.716 with super-solar metallicity toward SDSS J1323−0021. This is the highest metallicity intervening quasar absorber currently known, and is only the second super-solar absorber known to date. We provide a detailed study of this unique object from VLT/UVES spectroscopy. We derive [Zn/H]=+0.61, [Fe/H]=−0.51, [Cr/H]=< −0.53, [Mn/H] = −0.37, and [Ti/H] = −0.61. Observations and photoionisation models using the CLOUDY software confirm that the gas in this sub-DLA is predominantly neutral and that the abundance pattern is probably significantly different from a Solar pattern. Fe/Zn and Ti/Zn vary among the main velocity components by factors of ∼ 3 and ∼ 35, respectively, indicating non-uniform dust depletion. Mn/Fe is super-solar in almost all components, and varies by a factor of ∼ 3 among the dominant components. It would be interesting to observe more sub-DLA systems and determine whether they might contribute significantly toward the cosmic budget of metals.