Kavli Affiliate: George Efstathiou
| First 5 Authors: Boyuan Liu, Daniel Kessler, Thomas Gessey-Jones, Jiten Dhandha, Anastasia Fialkov
| Summary:
The first generation of stars, known as Population III (Pop III), played a
crucial role in the early Universe through their unique formation environment
and metal-free composition. These stars can undergo chemically homogeneous
evolution (CHE) due to fast rotation, becoming more compact and hotter/bluer
than their (commonly assumed) non-rotating counterparts. In this study, we
investigate the impact of Pop III CHE on the 21-cm signal and cosmic
reionization under various assumptions on Pop III star formation, such as their
formation efficiency, initial mass function, and transition to metal-enriched
star formation. We combine stellar spectra computed by detailed atmosphere
models with semi-numerical simulations of Cosmic Dawn and the Epoch of
Reionization ($zsim 6-30$). The key effect of CHE arises from the boosted
ionizing power of Pop III stars, which reduces the Pop III stellar mass density
required to reproduce the observed Thomson scattering optical depth by a factor
of $sim 2$. Meanwhile, the maximum 21-cm global absorption signal is shallower
by up to $sim 15$ mK (11%), partly due to the reduced Lyman-band emission from
CHE, and the large-scale ($ksim 0.2 rm cMpc^{-1}$) power drops by a factor
of a few at $zgtrsim 25$. In general, the effects of CHE are comparable to
those of Pop III star formation parameters, showing an interesting interplay
with distinct features in different epochs. These results highlight the
importance of metal-free/poor stellar evolution in understanding the early
Universe and suggest that future studies should consider joint constraints on
the physics of star/galaxy formation and stellar evolution.
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