Model-independent evidence in favour of an end to reionization by z ≈ 6
Date Issued
2015
Author(s)
Description
We thank the referee for a careful read of the manuscript and comments that improved the clarity of the text. IDM acknowledges support from NSF grants AST 08-06861 and AST 11-07682. Based in part on observations collected at the European Southern Observatory Very Large Telescope, Cerro Paranal, Chile – programmes 084.A-0390, 084.A-0550, 085.A-0299, 086.A-0162, 087.A-0607, and 268.A-5767. This paper also includes data obtained with the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution, and with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. We wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Facilities: Keck:II (ESI), MMT (Red Channel spectrograph), Magellan:Clay (MagE), VLT:Kueyen (X-shooter)
Abstract
We present new upper limits on the volume-weighted neutral hydrogen fraction, bar{x}_{H I}, at z ̃ 5-6 derived from spectroscopy of bright quasars. The fraction of the Lyα and Lyβ forests that is `dark' (with zero flux) provides the only model-independent upper limit on bar{x}_{H I}, requiring no assumptions about the physical conditions in the intergalactic medium or the quasar's unabsorbed UV continuum. In this work, we update our previous results using a larger sample (22 objects) of medium-depth (̃ few hours) spectra of high-redshift quasars obtained with the Magellan, MMT, and VLT. This significantly improves the upper bound on bar{x}_{H I} derived from dark pixel analysis to bar{x}_{H I} ≤ 0.06{+0.05 (1σ )} at z = 5.9 and bar{x}_{H I} ≤ 0.04{+0.05 (1σ )} at z = 5.6. These results provide robust constraints for theoretical models of reionization, and provide the strongest available evidence that reionization has completed (or is very nearly complete) by z ≈ 6.
Volume
447
Issue
1
Start page
499
Issn Identifier
0035-8711
Ads BibCode
2015MNRAS.447..499M
Rights
open.access
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