The Contribution of Supernovae to Cosmic Reionization

TL;DR

This paper estimates the contribution of supernovae to cosmic reionization, finding that SNe can significantly enhance the ionizing photon escape fraction and contribute up to 10% to hydrogen reionization.

Contribution

It introduces a quantitative assessment of supernovae's role in reionization, highlighting their higher escape fraction compared to stellar photons.

Findings

Supernovae have a higher escape fraction of ionizing photons than stars.

SNe can contribute more than stellar sources at certain hydrogen column densities.

Overall, SNe can increase the reionization fraction by up to 10%.

Abstract

While stars are widely discussed as the source of the high energy photons which reionized the universe, an additional source of ionizing photons that must also contribute to reionization in this scenario is the supernovae (SNe) which mark the end of the life of massive stars. Here we estimate the relative contributions of SNe and stars to reionization. While the rate at which ionizing photons are produced in SN shocks is well below that at which they are produced by stars, the harder spectra of radiation emitted from SNe leads to an enhanced escape fraction of SN generated photons relative to that of stellar photons. In particular, along a given line of sight out of a galaxy, we find that for neutral hydrogen column densities N_H >~10^18 cm^-2 the contribution to reionization from SNe is greater than that from stars. Drawing on the results of simulations presented in the literature, we find that the overall (line of sight-averaged) SNe shock-generated ionizing photon escape fraction is larger than the stellar photon escape fraction by a factor of \simeq 4 to \simeq 7, depending on the metallicity of the stellar population. Overall, our results suggest that the effect of SNe is an enhancement of up to ~ 10 percent in the fraction of hydrogen reionized by stellar sources. We briefly discuss the implications of our results for the population of galaxies responsible for reionization.