ABSORPTION-LINE SPECTROSCOPY OF GRAVITATIONALLY LENSED GALAXIES: FURTHER CONSTRAINTS ON THE ESCAPE FRACTION OF IONIZING PHOTONS AT HIGH REDSHIFT
AffiliationUniv Arizona, Dept Astron
Keywordscosmology: dark ages, reionization, first stars
MetadataShow full item record
PublisherIOP PUBLISHING LTD
CitationABSORPTION-LINE SPECTROSCOPY OF GRAVITATIONALLY LENSED GALAXIES: FURTHER CONSTRAINTS ON THE ESCAPE FRACTION OF IONIZING PHOTONS AT HIGH REDSHIFT 2016, 831 (2):152 The Astrophysical Journal
JournalThe Astrophysical Journal
Rights© 2016. The American Astronomical Society. All rights reserved.
Collection InformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at email@example.com.
AbstractThe fraction of ionizing photons escaping from high-redshift star-forming galaxies is a key obstacle in evaluating whether galaxies were the primary agents of cosmic reionization. We previously proposed using the covering fraction of low-ionization gas, measured via deep absorption-line spectroscopy, as a proxy. We now present a significant update, sampling seven gravitationally lensed sources at 4 < z < 5. We show that the absorbing gas in our sources is spatially inhomogeneous, with a median covering fraction of 66%. Correcting for reddening according to a dust-in-cloud model, this implies an estimated absolute escape fraction of similar or equal to 19% +/- 6%. With possible biases and uncertainties, collectively we find that the average escape fraction could be reduced to no less than 11%, excluding the effect of spatial variations. For one of our lensed sources, we have sufficient signal-tonoise ratio to demonstrate the presence of such spatial variations and scatter in its dependence on the Ly alpha equivalent width, consistent with recent simulations. If this source is typical, our lower limit to the escape fraction could be reduced by a further factor similar or equal to 2. Across our sample, we find a modest anticorrelation between the inferred escape fraction and the local star formation rate, consistent with a time delay between a burst and leaking Lyman continuum photons. Our analysis demonstrates considerable variations in the escape fraction, consistent with being governed by the small-scale behavior of star-forming regions, whose activities fluctuate over short timescales. This supports the suggestion that the escape fraction may increase toward the reionization era when star formation becomes more energetic and burst-like.
VersionFinal published version
SponsorsNASA [NAS 5-26555, HST-HF2-51359.001-A, HST-HF2-51334.001-A]; European Research Council [FP7/669253]; National Science Foundation [AST-1410155]; W. M. Keck Foundation