Staring at the Shadows of Archaic Galaxies: Damped Lyα and Metal Absorbers Toward a Young z ∼ 6 Weak-line Quasar

We characterize the Lyα halo and absorption systems toward PSO J083+11, a unique z = 6.3401 weak-line quasar, using Gemini Near-infrared Spectrograph, Magellan Folded-port Infrared Echellette, and Very Large Telescope Multi Unit Spectroscopic Explorer (MUSE) data. Strong absorptions by hydrogen and several metal lines (e.g., C II, Mg II, and O I) are discovered in the spectrum, which indicates the presence of: (i) a proximate subdamped Lyα (sub-DLA) system at z = 6.314 and (ii) a Mg II absorber at z = 2.2305. To describe the observed damping wing signal, we model the Lyα absorption with a combination of a sub-DLA with the neutral hydrogen column density of $\mathrm{log}{N}_{\mathrm{HI}}\,=\,20.03\pm 0.30\,{\mathrm{cm}}^{-2}$ and absorption from the intergalactic medium with a neutral fraction of around 10%. The sub-DLA toward PSO J083+11 has an abundance ratio of [C/O] = -0.04 ± 0.33 and metallicity of [O/H] = -2.19 ± 0.44, similar to those of low-redshift metal-poor DLAs. These measurements suggest that the sub-DLA might truncate PSO J083+11's proximity zone size and complicate the quasar lifetime measurement. However, this quasar shows no sign of a Lyα halo in the MUSE data cube, where the estimated 1σ limit of surface brightness is $2.76\times {10}^{-18}\,\mathrm{erg}\,{{\rm{s}}}^{-1}\,{\mathrm{cm}}^{-2}\,{\mathrm{arcsec}}^{-2}$ at an aperture size of 1″, or equivalent to a Lyα luminosity of ≤43.46 erg s^-1. This nondetection, while being only weak independent evidence on its own, is at least consistent with a young quasar scenario, as expected for a quasar with a short accretion timescale.