X-Ray Binaries and Ultra-Luminoius X-Ray Sources in Nearby and Distant Galaxies

We review recent results on populations of compact X-ray sources in normalgalaxies. The luminosity distributions of low and high mass X-ray binaries innearby galaxies appear to be described by the respective ``universal''luminosity functions, whose shapes do not vary significantly from galaxy togalaxy and the normalizations are proportional to the SFR (HMXBs) and stellarmass (LMXBs) of the host galaxy. There is a significant qualitative differencebetween XLFs of high and low mass X-ray binaries, reflecting the difference inthe accretion regimes in these two types of X-ray binaries. The high luminosity cut-off is by an order of magnitude larger for HMXBs --although bright sources, log(Lx)>39, are observed in both young and oldgalaxies, the truly ultraluminous ones, with log(Lx)~40-40.5, are associatedwith the regions of intense star formation and have not been detected so far inold stellar populations of elliptical and S0 galaxies. The Lx-SFR relation fordistant galaxies in the HDF-N indicates that ULXs at redshifts of z~0.2-1.3were not significantly more luminous than those observed in nearby galaxies.Comment: Progress of Theoretical Physics, in press. (Proceedings of the workshop "Stellar-Mass, Intermediate-Mass, and Supermassive Black Holes", Eds: K.Makishima and S.Mineshige.