A CRASH simulation of the contribution of binary stars to the epoch of reionization

TL;DR

This study uses 3D radiative transfer simulations to investigate how binary stars influence the epoch of reionization, affecting the intergalactic medium's properties, ionized bubble topology, and 21 cm power spectra.

Contribution

It provides new insights into the role of binary stars in reionization, showing their impact on ionization timing, bubble size distribution, and observable 21 cm signals.

Findings

Binary stars accelerate hydrogen and helium I reionization.

Gas ionized by binary stars is generally colder than that ionized by single stars.

Inclusion of binary stars leads to fewer small and more large ionized bubbles.

Abstract

We use a set of 3D radiative transfer simulations to study the effect that a large fraction of binary stars in galaxies during the epoch of reionization has on the physical properties of the intergalactic medium (i.e. the gas temperature and the ionization state of hydrogen and helium), on the topology of the ionized bubbles and on the 21 cm power spectra. Consistently to previous literature, we find that the inclusion of binary stars can speed up the reionization process of HI and HeI, while HeII reionization is still dominated by more energetic sources, especially accreting black holes. The earlier ionization attained with binary stars allows for more time for cooling and recombination, so that gas fully ionized by binary stars is typically colder than that ionized by single stars at any given redshift. With the same volume averaged ionization fraction, the inclusion of binary stars results in fewer small ionized bubbles and more large ones, with visible effects also on the large scales of the 21 cm power spectrum.