X-ray Binary Evolution Across Cosmic Time
  High redshift galaxies permit the study of the formation and evolution of
X-ray binary populations on cosmological timescales, probing a wide range of
metallicities and star-formation rates. In this paper, we present results from
a large scale population synthesis study that models the X-ray binary
populations from the first galaxies of the universe until today. We use as
input to our modeling the Millennium II Cosmological Simulation and the updated
semi-analytic galaxy catalog by Guo et al. (2011) to self-consistently account
for the star formation history and metallicity evolution of the universe. Our
modeling, which is constrained by the observed X-ray properties of local
galaxies, gives predictions about the global scaling of emission from X-ray
binary populations with properties such as star-formation rate and stellar
mass, and the evolution of these relations with redshift. Our simulations show
that the X-ray luminosity density (X-ray luminosity per unit volume) from X-ray
binaries in our Universe today is dominated by low-mass X-ray binaries, and it
is only at z>2.5 that high-mass X-ray binaries become dominant. We also find
that there is a delay of ~1.1 Gyr between the peak of X-ray emissivity from
low-mass Xray binaries (at z~2.1) and the peak of star-formation rate density
(at z~3.1). The peak of the X-ray luminosity from high-mass X-ray binaries (at
z~3.9), happens ~0.8 Gyr before the peak of the star-formation rate density,
which is due to the metallicity evolution of the Universe.
