A Metal-poor Damped Lyα System at Redshift 6.4

Abstract

We identify a strong Ly α damping wing profile in the spectrum of the quasar P183+05 at z  = 6.4386. Given the detection of several narrow metal absorption lines at z  = 6.40392, the most likely explanation for the absorption profile is that it is due to a damped Ly α system. However, in order to match the data a contribution of an intergalactic medium 5%–38% neutral or additional weaker absorbers near the quasar is also required. The absorption system presented here is the most distant damped Ly α system currently known. We estimate an H i column density of 10 20.68±0.25 cm −2 , metallicity [O/H] = −2.92 ± 0.32, and relative chemical abundances of a system consistent with a low-mass galaxy during the first Gyr of the universe. This object is among the most metal-poor damped Ly α systems known and, even though it is observed only ∼850 Myr after the big bang, its relative abundances do not show signatures of chemical enrichment by Population III stars.