On the rapid demise of Lyman-alpha emitters at z>7 due to the increasing incidence of optically thick absorption systems

S. Bolton, James; G. Haehnelt, Martin

Abstract

A variety of independent observational studies have now reported a significant decline in the fraction of Lyman-break galaxies which exhibit Ly-a emission over the redshift interval z=6-7. In combination with the strong damping wing extending redward of Ly-a in the spectrum of the bright z=7.085 quasar ULAS 1120+0641, this has strengthened suggestions that the hydrogen in the intergalactic medium (IGM) is still substantially neutral at z~7. Current theoretical models imply HI fractions as large as 40-90 per cent may be required to explain these data assuming there is no intrinsic evolution in the Ly-a emitter population. We propose that such large neutral fractions are not necessary. Based on a hydrodynamical simulation which reproduces the absorption spectra of high-redshift (z~6-7) quasars, we demonstrate that the opacity of the intervening IGM redward of rest-frame Ly-a can rise rapidly in average regions of the Universe simply because of the increasing incidence of absorption systems which are optically thick to Lyman continuum photons as the tail-end of reionisation is approached. Our simulations suggest these data do not require a large change in the IGM neutral fraction by several tens of per cent from z=6-7, but may instead be indicative of the rapid decrease in the typical mean free path for ionising photons expected during the final stages of reionisation.

Citation

S. Bolton, J., & G. Haehnelt, M. (2013). On the rapid demise of Lyman-alpha emitters at z>7 due to the increasing incidence of optically thick absorption systems. Monthly Notices of the Royal Astronomical Society, 429(2), 1695–1704. https://doi.org/10.1093/mnras/sts455

• Journal Article Type: Article
• Acceptance Date: Nov 20, 2012
• Publication Date: Feb 21, 2013
• Deposit Date: Sep 16, 2019
• Publicly Available Date: Nov 4, 2019
• Print ISSN: 0035-8711
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 429
• Issue: 2
• Pages: 1695–1704
• DOI: https://doi.org/10.1093/mnras/sts455
• Keywords: Cosmology and Nongalactic Astrophysics
• Public URL: https://nottingham-repository.worktribe.com/output/2462262
• Publisher URL: https://academic.oup.com/mnras/article/429/2/1695/1045458
• Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
• Contract Date: Nov 4, 2019