Evidence of patchy hydrogen reionization from an extreme Lyα trough below redshift six

Becker, George D.; Bolton, James S.; Madau, Piero; Pettini, Max; Ryan-Weber, Emma V.; Venemans, Bram P.

Abstract

© 2015 The Authors. We report the discovery of an extremely long (~110 Mpc h -1 ) and dark (τ eff ≳ 7) Lyα trough extending down to z ≃ 5.5 towards the z em ≃ 6.0 quasar ULAS J0148+0600. We use these new data in combination with Lya forest measurements from 42 quasars at 4.5 ≤ z em ≤ 6.4 to conduct an updated analysis of the line-of-sight variance in the intergalactic Lya opacity over 4 ≤ z ≤ 6. We find that the scatter in transmission among lines of sight near z ~ 6 significantly exceeds theoretical expectations for either a uniform ultraviolet background (UVB) or simple fluctuating UVB models in which the mean free path to ionizing photons is spatially invariant. The data, particularly near z ≃ 5.6-5.8, instead require fluctuations in the volume-weighted hydrogen neutral fraction that are a factor of 3 or more beyond those expected from density variations alone.We argue that these fluctuations are most likely driven by large-scale variations in the mean free path, consistent with expectations for the final stages of inhomogeneous hydrogen reionization. Even by z ≃ 5.6, however, a large fraction of the data are consistent with a uniform UVB, and by z ~ 5 the data are fully consistent with opacity fluctuations arising solely from the density field. This suggests that while reionization may be ongoing at z ~ 6, it has fully completed by z ~ 5.

Citation

Becker, G. D., Bolton, J. S., Madau, P., Pettini, M., Ryan-Weber, E. V., & Venemans, B. P. (2015). Evidence of patchy hydrogen reionization from an extreme Lyα trough below redshift six. Monthly Notices of the Royal Astronomical Society, 447(4), 3402-3419. https://doi.org/10.1093/mnras/stu2646

• Journal Article Type: Article
• Acceptance Date: Dec 12, 2014
• Online Publication Date: Jan 22, 2015
• Publication Date: Mar 11, 2015
• Deposit Date: Jul 4, 2016
• Publicly Available Date: Jul 4, 2016
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 447
• Issue: 4
• Pages: 3402-3419
• DOI: https://doi.org/10.1093/mnras/stu2646
• Keywords: Intergalactic Medium, Quasars, Absorption Lines, Cosmology, Observations, Dark Ages, Reionization, First Stars, Large-scale Structure of the Universe
• Public URL: https://nottingham-repository.worktribe.com/output/747772
• Publisher URL: http://mnras.oxfordjournals.org/content/447/4/3402
• Additional Information: This article has been published in Monthly Notices of the Royal Astronomical Society © 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
• Contract Date: Jul 4, 2016