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ON THE REDSHIFT EVOLUTION OF THE Ly alpha ESCAPE FRACTION AND THE DUST CONTENT OF GALAXIES
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
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2011 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 730, no 1, 8- p.Article in journal (Refereed) Published
Abstract [en]

The Ly alpha emission line has been proven to be a powerful tool for studying evolving galaxies at the highest redshift. However, in order to use Ly alpha as a physical probe of galaxies, it becomes vital to know the Ly alpha escape fraction (f(esc)(Ly alpha)). Unfortunately, due to the resonant nature of Ly alpha, f(esc)(Ly alpha) may vary unpredictably and requires empirical measurement. Here, we compile Ly alpha luminosity functions (LFs) between redshifts z = 0 and 8 and, combined with Ha and ultraviolet data, assess how f(esc)(Ly alpha) evolves with redshift. We find a strong upward evolution in f(esc)(Ly alpha) over the range z = 0.3-6, which is well fit by the power law f(esc)(Ly alpha) proportional to (1 + z)(xi) with xi = (2.57(-0.12)(+0.19)). This predicts that f(esc)(Ly alpha) should reach unity at z = 11.1. By comparing f(esc)(Ly alpha) and E(B-V) in individual galaxies we derive an empirical relationship between f(esc)(Ly alpha) and E(B-V), which includes resonance scattering and can explain the redshift evolution of f(esc)(Ly alpha) between z = 0 and 6 purely as a function of the evolution in the dust content of galaxies. Beyond z approximate to 6.5, f(esc)(Ly alpha) drops more substantially, an effect attributed to either ionizing photon leakage, or an increase in the neutral gas fraction of the intergalactic medium. While distinguishing between these two scenarios may be extremely challenging, by framing the problem this way we remove the uncertainty of the halo mass from Ly alpha-based tests of reionization. We finally derive a new method by which to estimate the dust content of galaxies, based purely upon the observed Ly alpha and UV LFs. These data are characterized by an exponential with an e-folding scale of z(EBV) approximate to 3.4.

Place, publisher, year, edition, pages
2011. Vol. 730, no 1, 8- p.
Keyword [en]
dark ages, reionization, first stars, galaxies: evolution, galaxies: high-redshift, galaxies: luminosity function, mass function, galaxies: star formation
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:su:diva-69455DOI: 10.1088/0004-637X/730/1/8ISI: 000288453600008OAI: oai:DiVA.org:su-69455DiVA: diva2:477519
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authorCount :6Available from: 2012-01-13 Created: 2012-01-12 Last updated: 2017-12-08Bibliographically approved

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