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Revisiting the Lyman Continuum Escape Crisis: Predictions for z > 6 from Local Galaxies

Faisst, Andreas L. (2016) Revisiting the Lyman Continuum Escape Crisis: Predictions for z > 6 from Local Galaxies. Astrophysical Journal, 829 (2). Art. No. 99. ISSN 0004-637X.

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The intrinsic escape fraction of ionizing Lyman continuum photons (f_(esc)) is crucial to understanding whether galaxies are capable of reionizing the neutral hydrogen in the early universe at z > 6. Unfortunately, it is not possible to access f_(esc) at z > 4 with direct observations, and the handful of measurements from low-redshift galaxies consistently find f_(esc) < 10%, while at least f_(esc) ∼ 10% is necessary for galaxies to dominate reionization. Here, we present the first empirical prediction of f_(esc) at z > 6 by combining the (sparsely populated) relation between [O III]/[O II] and f_(esc) with the redshift evolution of [O III]/[O II] as predicted from local high-z analogs selected by their Hα equivalent width. We find f_(esc) = 5.7(+8.3)(-3.3)% at z = 6 and f_(esc) = 10.4(+15.5)(-6.3)% at z = 9 for galaxies with log(M/M_⊙) ~ 9.0 (errors given as 1σ). However, there is a negative correlation with stellar mass and we find up to 50% larger f_(esc) per 0.5 dex decrease in stellar mass. The population-averaged escape fraction increases according to f_(esc) = f_(esc,0) ((1 + z) 3)^α, with f_(esc,0) = (2.3 ± 0.05)% and α = 1.17 ± 0.02 at z > 2 for log(M/M_⊙) ~ 9.0. With our empirical prediction of f_(esc) (thus fixing an important, previously unknown variable) and further reasonable assumptions on clumping factor and the production efficiency of Lyman continuum photons, we conclude that the average population of galaxies is just capable of reionizing the universe by z ∼ 6.

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URLURL TypeDescription Paper
Faisst, Andreas L.0000-0002-9382-9832
Alternate Title:Revisiting the Lyman Continuum Escape Crisis: Predictions for z > 6 from Local Galaxies
Additional Information:© 2016 The American Astronomical Society. Received 2016 May 20; accepted 2016 July 19; revised 2016 June 29; published 2016 September 27. The author would like to thank Dan Masters, Peter Capak, Janice Lee, and Kirsten Larson for valuable discussions that improved this manuscript. Furthermore, the author would like to thank the anonymous referee for very useful feedback. A.F. acknowledges support from the Swiss National Science Foundation.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Swiss National Science Foundation (SNSF)UNSPECIFIED
Subject Keywords:Galaxies: evolution; galaxies: high-redshift; galaxies: ISM
Issue or Number:2
Record Number:CaltechAUTHORS:20160928-141834080
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Official Citation:Andreas, L. F. (2016). Revisiting the Lyman Continuum Escape Crisis: Predictions for z > 6 from Local Galaxies. The Astrophysical Journal, 829(2), 99.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:70644
Deposited By: Melissa Ray
Deposited On:28 Sep 2016 22:21
Last Modified:03 Oct 2019 15:59

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