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Absorption Line Spectroscopy of Gravitationally-Lensed Galaxies: Further Constraints on the Escape Fraction of Ionizing Photons at High Redshift

Leethochawalit, Nicha and Jones, Tucker A. and Ellis, Richard S. and Stark, Daniel P. and Zitrin, Adi (2016) Absorption Line Spectroscopy of Gravitationally-Lensed Galaxies: Further Constraints on the Escape Fraction of Ionizing Photons at High Redshift. Astrophysical Journal, 831 (2). art. No. 152. ISSN 0004-637X. doi:10.3847/0004-637X/831/2/152.

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The 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 sime19% ± 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-to-noise ratio to demonstrate the presence of such spatial variations and scatter in its dependence on the Lyα 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 ≃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.

Item Type:Article
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URLURL TypeDescription Paper
Leethochawalit, Nicha0000-0003-4570-3159
Jones, Tucker A.0000-0001-5860-3419
Ellis, Richard S.0000-0001-7782-7071
Zitrin, Adi0000-0002-0350-4488
Additional Information:© 2016 American Astronomical Society. Received 2016 June 16; revised 2016 August 15; accepted 2016 August 31; published 2016 November 4. We acknowledge useful discussions with Phil Hopkins, Evan Kirby, Xiangcheng Ma, Brant Robertson, Brian Siana, and Alice Shapley. T.A.J. acknowledges support from NASA through Hubble Fellowship grant HST-HF2-51359.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. R.S.E. acknowledges support from the European Research Council through an Advanced Grant FP7/669253. D.P.S. acknowledges support from the National Science Foundation through grant AST-1410155. A.Z. is supported by NASA through Hubble Fellowship grant HST-HF2-51334.001-A awarded by STScI, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors acknowledge the very significant cultural role that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
Funding AgencyGrant Number
NASA Hubble FellowshipHST-HF2-51359.001-A
Space Telescope Science InstituteUNSPECIFIED
NASANAS 5-26555
European Research Council (ERC)FP7/669253
NASA Hubble FellowshipHST-HF2-51334.001-A
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:cosmology: dark ages, reionization, first stars ; galaxies: evolution; galaxies: formation; galaxies: ISM
Issue or Number:2
Record Number:CaltechAUTHORS:20161101-105703965
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Official Citation:Nicha Leethochawalit et al 2016 ApJ 831 152
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:71660
Deposited By: Ruth Sustaita
Deposited On:01 Nov 2016 18:34
Last Modified:11 Nov 2021 04:48

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