Consistently Reproducing Early Galaxy Observations and 21-cm Signal during the Epoch of Reionization

Abstract

In the standard cosmological model, galaxies forming within dark matter haloes are the primary drivers of the Epoch of Reionization (EoR). The complex physics of galaxy formation introduces scatter in the relation between halo mass and star-formation activity, with implications for the production and escape of ionising photons. In this work, we implement a stochastic source model in our cosmological radiative transfer simulations. We calibrate our model against the high-redshift ultraviolet luminosity function observed by JWST and observational constraints on Lyman-continuum leakage to constrain the ionising escape fraction. We find that stochastic star formation redistributes ionising emissivity toward lower-mass haloes, producing a more fragmented ionisation topology and delaying the growth of the largest ionised regions relative to the deterministic, observationally calibrated model. However, when the two models match total ionising photon production, their global neutral fractions and 21-cm power spectrum remain nearly indistinguishable, despite small differences in the morphology of individual ionised regions. Additionally, we establish a unified framework that lets us apply source models derived from computationally expensive hydrodynamical simulations (SPICE, FIRE-2 and Thesan) and investigate their impact on large-volume reionisation simulations, extending their prescriptions to scales of >100 Mpc. We find that these prescriptions produce distinct ionisation topologies and 21-cm statistical signatures, even when their global reionisation histories are similar. Our results highlight the importance of combining physically motivated galaxy formation prescriptions from hydrodynamical simulations with large-volume radiative transfer simulations to interpret forthcoming 21-cm observations and constrain the sources of cosmic reionisation.