A framework for modelling Population III stars in cosmological simulations

Abstract

Population III (Pop III) stars are the first generation of stars to form in the universe, emerging from primordial gas composed mainly of hydrogen and helium. They play a crucial role in ending the cosmic dark ages and initiating reionization. In this work, we present a comprehensive framework for modelling Pop III stars in cosmological simulations. This includes three key components: (1) an enhanced thermochemical network that tracks the equilibrium abundances of key catalytic species such as $\rm{H_2^+}$ and $\rm{H^-}$, which are crucial for forming molecular hydrogen in primordial gas; (2) detailed stellar spectra of Pop III stars computed from MESA evolutionary tracks and TLUSTY atmosphere models; and (3) comprehensive supernova feedback, including both Core-Collapse and Pair-Instability supernovae, with detailed elemental yields. We implement these improvements in AREPO-RT and test them using cosmological zoom-in simulations of a $1.95 \times 10^9$ $\rm M_\odot$ halo at $z=3$. Our results show that Pop III stars form at $z > 13$ and continue forming until $z \sim 5$, significantly affecting early galaxy evolution through radiation and energetic supernova feedback. The enhanced thermochemistry enables more efficient gas cooling, while Pop III feedback creates photo-heated diffuse gas and drives distinct metal enrichment patterns at $10 < z < 6$. The choice of IMF for Pop III stars critically determines the balance between radiative and mechanical feedback, with top-heavy choices producing stronger feedback and more metals but retaining less metal-enriched gas within the halo. Finally, we show that high-energy radiation from Pop III stars is necessary to explain the recent high-equivalent-width observations of the $\rm HeII$ line from a galaxy at $z\sim11$.