SIMBAD references

In the local Universe, integrated X-ray emission from high-mass X-ray binaries (HMXBs) is dominated by the brightest ultraluminous X-ray sources (ULXs) with luminosity >=10⁴⁰ erg s^–1. Such rare objects probably also dominated the production of X-rays in the early Universe. We demonstrate that a ULX with L_X ∼ 10⁴⁰-10⁴¹ erg s^–1 (isotropic-equivalent luminosity in the 0.1-10 keV energy band) shining for ∼10⁵ yr (the expected duration of a supercritically accreting phase in HMXBs) can significantly ionize the ISM in its host dwarf galaxy of total mass M ∼ 10⁷-10⁸ M_☉ and thereby reduce its opacity to soft X-rays. As a result, the fraction of the soft X-ray (below 1 keV) radiation from the ULX escaping into the intergalactic medium (IGM) can increase from ∼20-50 per cent to ∼30-80 per cent over its lifetime. This implies that HMXBs can induce a stronger heating of the IGM at z >= 10 compared to estimates neglecting the ULX feedback on the ISM. However, larger galaxies with M >= 3 x 10⁸ M_☉ could not be significantly ionized even by the brightest ULXs in the early Universe. Since such galaxies probably started to dominate the global star formation rate at z <= 10, the overall escape fraction of soft X-rays from the HMXB population probably remained low, <=30 per cent, at these epochs.