A Significantly Neutral Intergalactic Medium Around the Luminous z = 7 Quasar J0252–0503

Abstract

Luminous z  ≥ 7 quasars provide direct probes of the evolution of supermassive black holes (SMBHs) and the intergalactic medium (IGM) during the epoch of reionization (EoR). The Ly α damping wing absorption imprinted by neutral hydrogen in the IGM can be detected in a single EoR quasar spectrum, allowing the measurement of the IGM neutral fraction toward that line of sight. However, damping wing features have only been detected in two z  > 7 quasars in previous studies. In this paper, we present new high-quality optical and near-infrared spectroscopy of the z  = 7.00 quasar DES J025216.64–050331.8 obtained with Keck/Near-Infrared Echellette Spectrometer and Gemini/GMOS. By using the Mg ii single-epoch virial method, we find that it hosts a SMBH accreting at an Eddington ratio of λ Edd  = 0.7 ± 0.1, consistent with the values seen in other luminous z  ∼ 7 quasars. Furthermore, the Ly α region of the spectrum exhibits a strong damping wing absorption feature. The lack of associated metal absorption in the quasar spectrum indicates that this absorption is imprinted by a neutral IGM. Using a state-of-the-art model developed by Davies et al., we measure a volume-averaged neutral hydrogen fraction at z  = 7 of within 68% (95%) confidence intervals when marginalizing over quasar lifetimes of . This is the highest IGM neutral fraction yet measured using reionization-era quasar spectra.