Hydrogen reionization ends by z = 5.3: Lyman-α optical depth measured by the XQR-30 sample

Sarah E.I. Bosman, Frederick B. Davies, George D. Becker, Laura C. Keating, Rebecca L. Davies, Yongda Zhu, Anna Christina Eilers, Valentina D'Odorico, Fuyan Bian, Manuela Bischetti, Stefano V. Cristiani, Xiaohui Fan, Emanuele P. Farina, Martin G. Haehnelt, Joseph F. Hennawi, Girish Kulkarni, Andrei Mesinger, Romain A. Meyer, Masafusa Onoue, Andrea PallottiniYuxiang Qin, Emma Ryan-Weber, Jan Torge Schindler, Fabian Walter, Feige Wang, Jinyi Yang

Research output: Contribution to journalArticlepeer-review

99 Scopus citations

Abstract

The presence of excess scatter in the Ly-α forest at z ∼5.5, together with the existence of sporadic extended opaque Gunn-Peterson troughs, has started to provide robust evidence for a late end of hydrogen reionization. However, low data quality and systematic uncertainties complicate the use of Ly-α transmission as a precision probe of reionization's end stages. In this paper, we assemble a sample of 67 quasar sightlines at z > 5.5 with high signal-to-noise ratios of >10 per ≤15 km s-1 spectral pixel, relying largely on the new XQR-30 quasar sample. XQR-30 is a large program on VLT/X-Shooter which obtained deep (SNR > 20 per pixel) spectra of 30 quasars at z > 5.7. We carefully account for systematics in continuum reconstruction, instrumentation, and contamination by damped Ly-α systems. We present improved measurements of the mean Ly-α transmission over 4.9 < z < 6.1. Using all known systematics in a forward modelling analysis, we find excellent agreement between the observed Ly-α transmission distributions and the homogeneous-UVB simulations Sherwood and Nyx up to z ≤ 5.2 (<1σ), and mild tension (∼2.5σ) at z = 5.3. Homogeneous UVB models are ruled out by excess Ly-α transmission scatter at z ≥ 5.4 with high confidence (>3.5σ). Our results indicate that reionization-related fluctuations, whether in the UVB, residual neutral hydrogen fraction, and/or IGM temperature, persist in the intergalactic medium until at least z = 5.3 (t = 1.1 Gyr after the big bang). This is further evidence for a late end to reionization.

Original languageEnglish (US)
Pages (from-to)55-76
Number of pages22
JournalMonthly Notices of the Royal Astronomical Society
Volume514
Issue number1
DOIs
StatePublished - Jul 1 2022

Keywords

  • Dark ages
  • First stars
  • Intergalactic medium
  • Large-scale structure of Universe
  • Quasars: absorption lines
  • Reionization

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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