Vol. 634
Sect. 3. Cosmology

Contribution from stars stripped in binaries to cosmic reionization of hydrogen and helium

by Y. Götberg, S.E. de Mink, M. McQuinn, E. Zapartas, J.H. Groh, and C. Norman 2020, A&A, 634, A134

The presence of massive binary stars has been known to boost the production of ionizing radiation in the stellar populations: as such, it is extremely important to assess their contribution in the global ionizing budget during the reionization transition. In this work, the authors investigate the contribution of stars stripped of their hydrogen-rich envelopes in binaries. Such envelope-stripping is predicted to be the most common type of interaction in binaries as it is the fate of a third of all massive stars. Because stars over a wide range of masses can become stripped, the resulting ionizing radiation is emitted over an extended period of time after a starburst, therefore, these systems can boost the ionizing emission of stellar populations at late times. The authors find that stars stripped in binaries are likely to have had important effects on cosmic reionization since they could have provided ∼ 20% of the photons that reionized hydrogen in the Universe. On the other hand, the He ii-ionizing emission from stripped stars is not sufficient to compete with AGN and significantly impact the complete reionization of helium, although they might have contributed to the initial part of this process. Finally, the harder resulting spectra from stellar populations lead to an increased temperature of the IGM during reionization, although current high-redshift temperature measurements using the Lyα forest are probably not sensitive enough to detect such differences.