He II optical depth and UV escape fraction of galaxies

Abstract

We study the effect of H I ionizing photons escaping from high-redshift (high-z) galaxies have on the He II ionizing ultraviolet background (UVB) radiation. While these photons do not directly interact with He II ions, we show that they play an important role, through radiative transport, in modifying the shape of He II ionizing part of UVB spectrum. Within the observed range of UV escape from galaxies, we show that the rapid increase in He II Lyman alpha effective optical depth at z~2.7 can naturally be explained by radiative transport effects. Therefore, the relationship between a well measured He II Lyman alpha effective optical depth and the redshift in the post-He II reionization era can be used to place additional constraints on the redshift evolution of UV escape from high-z galaxies. Our study also suggests that the escape fraction of H I ionizing photons from galaxies has an important role in the fluctuations of the He II ionizing UVB.

Published in MNRAS Letters, replacement of a figure and minor text changes corresponding to published version

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• Cosmic reionization after Planck II: contribution from quasars
• Photon underproduction crisis: Are QSOs sufficient to resolve it?
• Intergalactic Lyman continuum photon budget in the past 5 billion years
• Star formation history, dust attenuation and extragalactic background light
• Constraints on QSO emissivity using H I and He II Lyman alpha forest
• A Pair of O VI and Broad Ly-alpha Absorbers Probing Warm Gas in a Galaxy Group Environment at z ~ 0.4
• The Escape Fraction of Ionizing Radiation from Galaxies
• Effect of non-equilibrium ionization on derived physical conditions of the high-$z$ intergalactic medium
• Implications of an updated ultraviolet background for the ionization mechanisms of intervening Ne VIII absorbers
• How Robust are the Inferred Density and Metallicity of the Circumgalactic Medium?
• The impact of temperature fluctuations on the large-scale clustering of the Ly$\alpha$ forest
• Probing reionization using quasar near-zones at redshift z ~ 6
• Ultraviolet background fluctuations with clustered sources
• Physical conditions in high$-$z optically thin C III absorbers: Origin of cloud sizes and associated correlations