Reionization with Simba: How much does astrophysics matter in modeling cosmic reionization?

TL;DR

This study compares simple deterministic models with detailed hydrodynamic simulations for cosmic reionization, finding that simplified models are generally sufficient for large-scale structure predictions despite astrophysical variability.

Contribution

It demonstrates that detailed source modeling introduces minimal changes to large-scale reionization morphology, validating the use of simplified models for cosmological studies.

Findings

Ionization morphology is largely unaffected by source variability.

Power spectrum amplitude varies less than 10% during reionization.

Simplified models are effective for large-scale reionization predictions.

Abstract

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 modelling reionization of using more detailed models for the ionizing sources as identified within the $100~{\rm Mpc/h}$ cosmological hydrodynamic simulation {\sc Simba}, coupled with post-processed radiative transfer. Comparing with simple (one-to-one) models, the main difference of using {\sc 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.