The 21-cm signal from the cosmic dawn: metallicity dependence of high-mass X-ray binaries
Abstract
X-rays from high-mass X-ray binaries (HMXBs) are likely the main source of heating of the intergalactic medium (IGM) during Cosmic Dawn (CD), before the completion of reionization. This Epoch of Heating (EoH; z ~10-15) should soon be detected via the redshifted 21-cm line from neutral hydrogen, allowing us to indirectly study the properties of HMXBs in the unseen, first galaxies. Low-redshift observations, as well as theoretical models, imply that the integrated X-ray luminosity to star formation rate of HMXBs (LX/SFR) should increase in metal-poor environments, typical of early galaxies. Here, we study the impact of the metallicity (Z) dependence of LX/SFR during the EoH. For our fiducial models, galaxies with star formation rates of order 10-3-$10^{-1}\, M_\odot$ yr-1 and metallicities of order 10-3-$10^{-2}\, Z_\odot$ are the dominant contributors to the X-ray background (XRB) during this period. Different LX/SFR-Z relations result in factors of ~ 3 differences in these ranges, as well as in the mean IGM temperature and the large-scale 21-cm power, at a given redshift. We compute mock 21-cm observations adopting as a baseline a 1000 h integration with the upcoming Square Kilometer Array (SKA) for two different LX/SFR-Z relations. We perform inference on these mock observations using the common simplification of a constant LX/SFR, finding that constant LX/SFR models can recover the IGM evolution of the more complicated LX/SFR-Z simulations only during the EoH. At z < 10, where the typical galaxies are more polluted, constant LX/SFR models overpredict the XRB and its relative contribution to the early stages of the reionization.
- Publication:
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Monthly Notices of the Royal Astronomical Society
- Pub Date:
- July 2022
- DOI:
- 10.1093/mnras/stac1226
- arXiv:
- arXiv:2203.10851
- Bibcode:
- 2022MNRAS.513.5097K
- Keywords:
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- galaxies: high-redshift;
- (galaxies:) intergalactic medium;
- (cosmology:) dark ages;
- reionization;
- first stars;
- cosmology: theory;
- (cosmology:) early Universe;
- X-rays: binaries;
- X-rays: diffuse background;
- X-rays: galaxies;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- doi:10.1093/mnras/stac1226