High Mass X-ray Binaries and the Cosmic 21-cm Signal: Impact of Host Galaxy Absorption
Feb 1, 20179 pages
Published in:
- Mon.Not.Roy.Astron.Soc. 469 (2017) 1, 1166-1174
- Published: Jul 21, 2017
e-Print:
- 1702.00409 [astro-ph.CO]
DOI:
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Abstract: (Oxford University Press)
By heating the intergalactic medium (IGM) before reionization, X-rays are expected to play a prominent role in the early Universe. The cosmic 21-cm signal from this ‘epoch of heating’ (EoH) could serve as a clean probe of high-energy processes inside the first galaxies. Here, we improve on prior estimates of this signal by using high-resolution hydrodynamic simulations to calculate the X-ray absorption due to the interstellar medium (ISM) of the host galaxy, typically residing in haloes with mass 10^7.5–8.5 M_⊙ at z ∼ 8–15. X-rays absorbed inside the host galaxy are unable to escape into the IGM and contribute to the EoH. We find that the X-ray opacity through these galaxies can be approximated by a metal-free ISM with a typical column density of . We compute the resulting 21-cm signal by combining these ISM opacities with public spectra of high-mass X-ray binaries (thought to be important X-ray sources in the early Universe). Our results support ‘standard scenarios’ in which the X-ray heating of the IGM is inhomogeneous, and occurs before the bulk of reionization. The large-scale (k ∼ 0.1 Mpc^−1) 21-cm power reaches a peak of ≈100 mK^2 at z ∼ 10–15, with the redshift depending on the cosmic star formation history. Our main results can be reproduced by approximating the X-ray emission from high-mass X-ray binaries by a power law with energy index α ≈ 1, truncated at energies below 0.5 keV.Note:
- 9 pages, 8 figures, submitted to MNRAS
- galaxies: evolution
- intergalactic medium
- dark ages, reionization, first stars
- early Universe
- cosmology: theory
- X-rays: diffuse background
References(74)
Figures(13)