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

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

doi:10.1093/mnras/stac1046

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

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Farina, Emanuele P.
Cosmology, MPI for Astrophysics, Max Planck Society;

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Citation

Bosman, S. E. I., Davies, F. B., Becker, G. D., Keating, L. C., Davies, R. L., Zhu, Y., et al. (2022). Hydrogen reionization ends by z = 5.3: Lyman-α optical depth measured by the XQR-30 sample. Monthly Notices of the Royal Astronomical Society, 514(1), 55-76. doi:10.1093/mnras/stac1046.

Cite as: https://hdl.handle.net/21.11116/0000-000B-5837-5

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.