X-ray Binary Evolution Across Cosmic Time

TL;DR

This study models the evolution of X-ray binary populations across cosmic time using cosmological simulations, revealing how their contributions to X-ray luminosity change with redshift and metallicity.

Contribution

It provides the first comprehensive population synthesis model linking X-ray binary evolution to cosmic star formation and metallicity history, constrained by local galaxy observations.

Findings

Low-mass X-ray binaries dominate current X-ray luminosity density.

High-mass X-ray binaries dominate at redshifts above 2.5.

Delay of ~1.1 Gyr between low-mass X-ray binary peak and star formation peak.

Abstract

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.