A significantly neutral intergalactic medium around the luminous z = 7 Quasar J0252–0503

Feige Wang, Frederick B. Davies, Jinyi Yang, Joseph F. Hennawi, Xiaohui Fan, Aaron J. Barth, Linhua Jiang, Xue Bing Wu, Dale M. Mudd, Eduardo Bañados, Fuyan Bian, Roberto Decarli, Anna Christina Eilers, Emanuele Paolo Farina, Bram Venemans, Fabian Walter, Minghao Yue

Research output: Contribution to journalArticlepeer-review


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 Lyα 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 towards 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/NIRES and Gemini/GMOS. By using the Mg ii single-epoch virial method, we find that it hosts a (1.39 ± 0.16) × 109 M⊙ SMBH accreting at an Eddington ratio of λEdd = 0.7 ±0.1, consistent with the values seen in other luminous z ∼ 7 quasars. Furthermore, the Lyα 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 hxHIi = 0.70+00..2023(+00..2848) within 68% (95%) confidence intervals when marginalizing over quasar lifetimes of 103 ≤ tQ ≤ 108 yr. This is the highest IGM neutral fraction yet measured using reionization-era quasar spectra.

Original languageEnglish (US)
JournalUnknown Journal
StatePublished - Apr 22 2020


  • Cosmology: observations
  • Early universe
  • Galaxies: active
  • Galaxies: high-redshift
  • Quasars: individual (DES J025216.64–050331.8)

ASJC Scopus subject areas

  • General

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