Population III X-ray binaries and their impact on the early universe

• Published in: Monthly notices of the Royal Astronomical Society Vol. 521; no. 3; pp. 4039 - 4055
• Main Authors: Sartorio, Nina S, Fialkov, A, Hartwig, T, Mirouh, G M, Izzard, R G, Magg, M, Klessen, R S, Glover, S C O, Chen, L, Tarumi, Y, Hendriks, D D
• Format: Journal Article
• Language: English
• Published: Oxford University Press 01-05-2023
• Subjects: (cosmology:) early Universe; (cosmology:) diffuse radiation; stars: Population III; X-rays: binaries
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stad697

ABSTRACT
The first population of X-ray binaries (XRBs) is expected to affect the thermal and ionization states of the gas in the early Universe. Although these X-ray sources are predicted to have important implications for high-redshift observable signals, such as the hydrogen 21-cm signal from cosmic dawn and the cosmic X-ray background, their properties are poorly explored, leaving theoretical models largely uninformed. In this paper we model a population of X-ray binaries arising from zero metallicity stars. We explore how their properties depend on the adopted initial mass function (IMF) of primordial stars, finding a strong effect on their number and X-ray production efficiency. We also present scaling relations between XRBs and their X-ray emission with the local star formation rate, which can be used in sub-grid models in numerical simulations to improve the X-ray feedback prescriptions. Specifically, we find that the uniformity and strength of the X-ray feedback in the intergalactic medium is strongly dependant on the IMF. Bottom-heavy IMFs result in a smoother distribution of XRBs, but have a luminosity orders of magnitude lower than more top-heavy IMFs. Top-heavy IMFs lead to more spatially uneven, albeit strong, X-ray emission. An intermediate IMF has a strong X-ray feedback while sustaining an even emission across the intergalactic medium. These differences in X-ray feedback could be probed in the future with measurements of the cosmic dawn 21-cm line of neutral hydrogen, which offers us a new way of constraining population III IMF.