The role of metallicity in high mass X-ray binaries in galaxy formation
  models
  Recent theoretical works claim that high-mass X-ray binaries (HMXBs) could
have been important sources of energy feedback into the interstellar and
intergalactic media, playing a major role in the reionization epoch. A
metallicity dependence of the production rate or luminosity of the sources is a
key ingredient generally assumed but not yet probed. Aims: Our goal is to
explore the relation between the X-ray luminosity (Lx) and star formation rate
of galaxies as a possible tracer of a metallicity dependence of the production
rates and/or X-ray luminosities of HMXBs. Methods: We developed a model to
estimate the Lx of star forming galaxies based on stellar evolution models
which include metallicity dependences. We applied our X-ray binary models to
galaxies selected from hydrodynamical cosmological simulations which include
chemical evolution of the stellar populations in a self-consistent way.
Results: Our models successfully reproduce the dispersion in the observed
relations as an outcome of the combined effects of the mixture of stellar
populations with heterogeneous chemical abundances and the metallicity
dependence of the X-ray sources. We find that the evolution of the Lx as a
function of SFR of galaxies could store information on possible metallicity
dependences of the HMXB sources. A non-metallicity dependent model predicts a
non-evolving relation while any metallicity dependence should affect the slope
and the dispersion as a function of redshift. Our results suggest the
characteristics of the Lx evolution can be linked to the nature of the
metallicity dependence of the production rate or the Lx of the stellar sources.
By confronting our models with current available observations of strong
star-forming galaxies, we find that only chemistry-dependent models reproduce
the observed trend for z < 4.
