2005/11/16 by G. Fabbiano · 1 citation
Physics and Astronomy · #astro-ph
paper · pdf · doi:10.1146/annurev.astro.44.051905.092519
published as Ann.Rev.Astron.Astrophys.44:323-366,2006 · 40 pages. This is a review submitted to Annual Review of Astronomy & Astrophysics Comments are welcome and will be considered in a revised version
arxiv created 2005/11/16 · arxiv updated 2009/12/01
Today's sensitive, high-resolution X-ray observations allow the study of populations of X-ray sources, in the luminosity range of Galactic X-ray binaries, in galaxies as distant as 20-30 Mpc. The traditional astronomical tools of photometric diagrams and luminosity functions are now applied to these populations, providing a direct probe of the evolved binary component of different stellar populations. The study of the X-ray populations of E and S0 galaxies has revamped the debate on the formation and evolution of low-mass X-ray binaries (LMXBs) and on the role of globular clusters in these processes. While overall stellar mass drives the amount of X-ray binaries in old stellar populations, the amount of sources in star forming galaxies is related to the star formation rate. Short-lived, luminous, high-mass binaries (HMXBs) dominate these young populations. The most luminous sources in these systems are the debated ULXs, which have been suggested to be ~100-1000 Msol black holes, but could alternatively include a number of binaries with stellar mass black holes. Very soft sources have also been discovered in many galaxies and their nature is currently being debated. Observations of the deep X-ray sky, and comparison with deep optical surveys, are providing the first evidence of the X-ray evolution of galaxies.