Reionization with Simba: How Much Does Astrophysics Matter in Modeling Cosmic Reionization?

Traditional large-scale models of reionization usually employ simple deterministic relations between halo mass and luminosity to predict how reionization proceeds. We here examine the impact on modeling reionization of using more detailed models for the ionizing sources as identified within the 100 h (-1) Mpc cosmological hydrodynamic simulation Simba, coupled with postprocessed radiative transfer. Comparing with simple (one-to-one) models, the main difference with using Simba sources is the scatter in the relation between dark matter halos and star formation, and hence ionizing emissivity. We find that, at the power spectrum level, the ionization morphology remains mostly unchanged, regardless of the variability in the number of sources or escape fraction. In particular, the power spectrum shape remains unaffected and its amplitude changes slightly by less than 5%-10%, throughout reionization, depending on the scale and neutral fraction. Our results show that simplified models of ionizing sources remain viable to efficiently model the structure of reionization on cosmological scales, although the precise progress of reionization requires accounting for the scatter induced by astrophysical effects.

Automated summary

Traditional large-scale models of reionization usually use simple deterministic relations between halo mass and luminosity to predict reionization. This study examines the impact of using more detailed models for ionizing sources and finds that the scatter in the relation between dark matter halos and star formation affects the model. However, at the power spectrum level, the ionization morphology remains mostly unchanged regardless of the variability in the number of sources or escape fraction.