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New constraints on Lyman-alpha opacity with a sample of 62 quasars at z > 5.7

Bosman, SEI; Fan, X; Jiang, L; Reed, S; Matsuoka, Y; Becker, G; Haehnelt, M; (2018) New constraints on Lyman-alpha opacity with a sample of 62 quasars at z > 5.7. Monthly Notices of the Royal Astronomical Society , 479 (1) pp. 1055-1076. 10.1093/mnras/sty1344. Green open access

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We present measurements of the mean and scatter of the intergalactic medium (IGM) Lyman-α opacity at 4.9 < z < 6.1 along the lines of sight of 62 quasars at zsource> 5.7, the largest sample assembled at these redshifts to date by a factor of two. The sample size enables us to sample cosmic variance at these redshifts more robustly than ever before. The spectra used here were obtained by the Sloan Digital Sky Survey, Dark Energy Survey–VISTA Hemisphere Survey, and Subaru High-z Exploration of Low-Luminosity Quasars collaborations, drawn from the Echellette Spectrograph and Imager and X-Shooter archives, reused from previous studies or observed specifically for this work. We measure the effective optical depth of Lyman-α in bins of 10, 30, 50, and 70 cMpc h−1, construct cumulative distribution functions under two treatments of upper limits on flux and explore an empirical analytic fit to residual Lyman-α transmission. We verify the consistency of our results with those of previous studies via bootstrap resampling and confirm the existence of tails towards high values in the opacity distributions, which may persist down to z ∼ 5.2. Comparing our results with predictions from cosmological simulations, we find further strong evidence against models that include a spatially uniform ionizing background and temperature–density relation. We also compare to IGM models that include either a fluctuating ultraviolet background dominated by rare quasars or temperature fluctuations due to patchy reionization. Although both models produce better agreement with the observations, neither fully captures the observed scatter in IGM opacity. Our sample of 62 z > 5.7 quasar spectra opens many avenues for future study of the reionization epoch.

Type: Article
Title: New constraints on Lyman-alpha opacity with a sample of 62 quasars at z > 5.7
Open access status: An open access version is available from UCL Discovery
DOI: 10.1093/mnras/sty1344
Publisher version: https://doi.org/10.1093/mnras/sty1344
Language: English
Additional information: This is the published version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: intergalactic medium, quasars: absorption lines, dark ages, reionization, first stars
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10055762
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