Presentation #240.01 in the session “Galaxies During Reionization or Just After”.
Observations of nearby star-forming regions suggest that binary stars are common, even representing the majority of massive stars. Their evolutionary effects result in harder spectral energy distributions, generation of H I-ionizing radiation for longer times, and higher Lyman continuum escape fractions from galaxies than their single star counterparts, in sum, having potentially critical implications for H I reionization and early galaxy characteristics and processes. Incorporating the Binary Population and Spectral Synthesis (BPASS) models into our cosmological hydrodynamic simulations with in-situ radiative transfer, we have investigated from z=5-8 the effects of binary stars on star formation, H I and early He II reionization, the IGM and CGM, and on very high redshift metals, such as those observed in quasar absorption spectra. We find that, in comparison to the single star control model, binary stars produce an accelerated H I reionization history, but simultaneously increase typical gas temperatures and in so doing reduce the global star formation rate density, leading to a slowing in the rate of He II ionization by z=5. The line-of-sight number density of low ionization metal absorbers is reduced, while the abundance of high ionization systems is substantially increased. From these results, we conclude that while binary stars do produce the anticipated effects of aiding H I reionization and ionizing the CGM with their bluer spectra, they also introduce a more complex interplay between stellar emissivities, gas heating, and star formation whose ultimate impact is dependent on the time frame under consideration.