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

Luminous z 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 alpha 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 (1.39 +/- 0.16) x 10(9) M-circle dot SMBH accreting at an Eddington ratio of lambda(Edd) = 0.7 +/- 0.1, consistent with the values seen in other luminous z similar to 7 quasars. Furthermore, the Lya 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 volumeaveraged neutral hydrogen fraction at z = 7 of < x(H I)> = 0.70(-0.23)(+0.20) [GRAPHICS] within 68% (95%) confidence intervals when marginalizing over quasar lifetimes of 10(3) <= t(Q) <= 10(8) yr. This is the highest IGM neutral fraction yet measured using reionization-era quasar spectra.