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Book Chapter

X-ray binaries in external galaxies


Gilfanov,  Marat
High Energy Astrophysics, MPI for Astrophysics, Max Planck Society;

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Gilfanov, M., Fabbiano, G., Lehmer, B., & Zezas, A. (2022). X-ray binaries in external galaxies. In A. Santangelo, & C. Bambi (Eds.), Handbook of X-ray and Gamma-ray Astrophysics. Singapore: Springer Singapore. doi:10.1007/978-981-16-4544-0_108-1.

Cite as: https://hdl.handle.net/21.11116/0000-000D-3BF5-D
X-ray appearance of normal galaxies is mainly determined by X-ray binaries powered by accretion onto a neutron star or a stellar mass black hole. Their populations scale with the star-formation rate and stellar mass of the host galaxy, and their X-ray luminosity distributions show a significant split between star-forming and passive galaxies, both facts being consequences of the dichotomy between high- and low-mass X-ray binaries. Metallicity, IMF and stellar age dependencies, and dynamical formation channels add complexity to this picture. The numbers of high-mass X-ray binaries observed in star-forming galaxies indicate quite high probability for a massive star to become an accretion-powered X-ray source once upon its lifetime. This explains the unexpectedly high contribution of X-ray binaries to the cosmic X-ray background, of the order of ∼10%, mostly via X-ray emission of faint star-forming galaxies located at moderate redshifts which may account for the unresolved part of the CXB. Cosmological evolution of the LX −SFR relation can make high-mass X-ray binaries a potentially significant factor in (pre)heating of intergalactic medium in the early Universe.