The Escape Fraction of Ionizing Radiation from Primordial Galaxies. (arXiv:1212.4452v1 [astro-ph.CO])

The Escape Fraction of Ionizing Radiation from Primordial Galaxies. (arXiv:1212.4452v1 [astro-ph.CO]):
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.