The Escape Fraction of Ionizing Radiation from Galaxies

Abstract

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. We present semi-analytic calculations of the escape fraction of ionizing radiation for both hydrogen and helium from galaxies ranging from primordial systems to disk-type galaxies that are not heavily dust-obscured. We consider variations in the galaxy density profile, source type, location, and spectrum, and gas overdensity/distribution factors. For sufficiently hard first-light sources, the helium ionization fronts closely track or 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 galaxy 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.

43 pages, 9 figures, accepted in ApJ, comments welcome

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• Direct Detection of Lyman Continuum Escape from Local Starburst Galaxies with the Cosmic Origins Spectrograph
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• Lyman Radiation Hydrodynamics of Turbulent H II Regions in Molecular Clouds: A Physical Origin of LyC Leakage and the Associated Ly$\alpha$ Spectra
• Decoding the X-ray Properties of Pre-Reionization Era Sources
• Semi-analytic forecasts for JWST -- IV. Implications for cosmic reionization and LyC escape fraction
• The Metagalactic Ionizing Background: A Crisis in UV Photon Production or Incorrect Galaxy Escape Fractions?
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• Intergalactic Lyman continuum photon budget in the past 5 billion years
• New Constraints on the Escape of Ionizing Photons From Starburst Galaxies Using Ionization-Parameter Mapping
• Semi-analytic forecasts for JWST -- V. AGN luminosity functions and helium reionization at z = 2-7
• Empirically Constrained Predictions for Metal-Line Emission from the Circumgalactic Medium
• A case study of hurdle and generalized additive models in astronomy: the escape of ionizing radiation
• Global Correlations Between the Radio Continuum, Infrared and CO Emission in Dwarf Galaxies
• The prospects for observing [OIII] 52 micron emission from galaxies during the Epoch of Reionization
• Flux sensitivity requirements for the detection of Lyman continuum radiation drop-ins from star-forming galaxies below redshifts of 3
• Cosmic reionization of hydrogen and helium: contribution from both mini-quasars and stars
• Modelling the escape of Lyman Continuum photons from galaxies in the Epoch of Reionization
• Topological models to infer multiphase interstellar medium properties
• Dark Matter Annihilation in the First Galaxy Halos