Effects of Metallicity on High Mass X-ray Binary Formation

TL;DR

This study investigates how metallicity influences the formation of high mass X-ray binaries (HMXBs) in low-metallicity galaxies, suggesting increased HMXB production at lower metallicities which could impact early Universe heating.

Contribution

It provides the first focused analysis of metallicity effects on HMXB formation using a uniform sample of blue compact dwarf galaxies, employing Bayesian methods to quantify this dependence.

Findings

HMXB production increases at lower metallicity levels.

XLF normalization is 4.45 times higher in the lowest metallicity range.

Results imply HMXBs significantly contributed to early Universe reheating.

Abstract

The heating of the intergalactic medium in the early, metal-poor Universe may have been partly due to radiation from high mass X-ray binaries (HMXBs). Previous investigations on the effect of metallicity have used galaxies of different types. To isolate the effects of metallicity on the production of HMXBs, we study a sample consisting only of 46 blue compact dwarf galaxies (BCDs) covering metallicity in the range 12+log(O/H) of 7.15 to 8.66. To test the hypothesis of metallicity dependence in the X-ray luminosity function (XLF), we fix the XLF form to that found for near-solar metallicity galaxies and use a Bayesian method to constrain the XLF normalization as a function of star formation rate (SFR) for three different metallicity ranges in our sample. We find an increase by a factor of 4.45 $\pm$ 2.04 in the XLF normalization between the metallicity ranges 7.1-7.7 and 8.2-8.66 at a statistical significance of 99.79 per cent. Our results suggest that HMXB production is enhanced at low metallicity, and consequently that HMXBs may have contributed significantly to the reheating of the early Universe.