Andrew Benson, Aparna Venkatesan, J. Michael Shull
The escape of ionizing radiation from galaxies plays a critical role in the evolution of gas in galaxies, and the heating and ionization history of the intergalactic medium. Here, we present semi-analytic calculations of the escape fraction of ionizing radiation for both hydrogen and helium from primordial galaxies, as well as analytic derivations of these quantities. We consider variations in the galaxy density profile, source type, location, and spectrum, and gas clumping/distribution factors. For sufficiently hard first-light sources, the helium ionization fronts closely track or even advance beyond that of hydrogen. Key new results in this work include calculations of the escape fractions for He I and He II ionizing radiation, and the impact of partial ionization from X-rays from early AGN or stellar clusters on the escape fractions from primordial halos. When factoring in frequency-dependent effects, we find that X-rays play an important role in boosting the escape fractions for both hydrogen and helium, but especially for He II. We briefly discuss the implications of these results for recent observations of the He II reionization epoch at low redshifts, as well as the UV data and emission-line signatures from early galaxies anticipated from future satellite missions.
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http://arxiv.org/abs/1212.4452
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