Impact of Population III homogeneous stellar evolution on early cosmic reionisation

Abstract

Context: Population III (Pop III) stars may be fast rotating. An expected consequence of fast rotation is strong internal mixing that deeply affects their evolutionary tracks in the Hertzsprung-Russell diagram and hence their ionising power. aims: We investigate the impact on the ionising power of Pop III stars in an extreme case of internal mixing, the one leading to chemically homogeneous evolution (CHE). In that situation, during the main sequence phase, the star keeps the same chemical composition from its center to its surface. Homogeneous stars have larger effective temperatures and luminosities than stars evolving non-homogeneously and thus are stronger ionising sources. Methods: The stellar evolution models are based on $n=3$ polytropes with a time varying hydrogen mass fraction. The ionisation model employs the self-similar champagne flow solution from Shu et al. (2002), as well as numerical simulations for the stochastic treatment of star clusters over a grid of redshifts and halo masses. Results: We find that haloes containing chemically homogeneous stars have an escape fraction of ionising photons about twice that of haloes containing classical Pop III stars. By extrapolating the high-$z$ ionisation history powered by Pop III stars (at $z\gtrsim 15$) to the post-reionisation epoch, we derive the Thomson scattering optical depth $\tau$, which is compared with the value measured by $\text{Planck}$. We find that $\tau$ is overproduced by $\sim 1.5-5\sigma$, when all Pop III stars evolve homogeneously. This indicates that CHE is unlikely to be realised in the majority of Pop III stars, although the present study cannot exclude that a fraction of them undergoes CHE. Conclusions: Fast rotation might have a significant impact on the ionising budget of Pop III stars, and thus on early cosmic reionisation.

Accepted for publication in A&A (12 August 2022); 13 pages, 9 figures

References in corpus (23)

• Primordial Star Formation under the Influence of Far Ultraviolet Radiation: 1540 Cosmological Halos and the Stellar Mass Distribution
• The Mass Spectrum of the First Stars
• Effects of rotation on the evolution of primordial stars
• Introducing the THESAN project: radiation-magnetohydrodynamic simulations of the epoch of reionization
• Formation of massive black holes in rapidly growing pre-galactic gas clouds
• The First Billion Years Project: The escape fraction of ionizing photons in the epoch of reionization
• Two populations of metal-free stars in the early Universe
• The ASTRID Simulation: Galaxy Formation and Reionization
• The Impact of the First Galaxies on Cosmic Dawn and Reionization
• The first generation of stars in LCDM cosmology
• Constraining the primordial initial mass function with stellar archaeology
• Ultra-luminous X-ray sources and neutron-star-black-hole mergers from very massive close binaries at low metallicity
• When did Population III star formation end?
• Formation sites of Population III star formation: The effects of different levels of rotation and turbulence on the fragmentation behavior of primordial gas
• The Efficiency of Stellar Reionization: Effects of Rotation, Metallicity, and Initial Mass Function
• Properties of WNh stars in the Small Magellanic Cloud: evidence for homogeneous evolution
• The Effects of Population III X-ray and Radio Backgrounds on the Cosmological 21-cm Signal
• The Effect of Galactic Properties on the Escape Fraction of Ionizing Photons
• Public Release of A-SLOTH: Ancient Stars and Local Observables by Tracing Halos
• Constraining First Star Formation with 21cm-Cosmology
• Grids of stellar models with rotation: V. Models from 1.7 to 120 Msun at zero metallicity
• Trapping of HII regions in Population III star formation
• Lyman-Werner Escape Fractions from the First Galaxies

Cited by in corpus (1)

• Characterization of Population III Stars with Stellar Atmosphere and Evolutionary Modeling and Predictions of their Observability with the James Webb Space Telescope