HMXB, ULX and star formation

Based on recent X-ray observations of the Milky Way, Magellanic Clouds and nearby starburst galaxies we study population of high mass X-ray binaries, their connection with ultra-luminous X-ray sources and relation to the star formation. Although more subtle SFR dependent effects are likely to exist, the data in the lg(LX) ∼ 36 − 40.5 luminosity range are broadly consistent with existence of a " universal " luminosity function of HMXBs, which can be roughly described as a power law with differential slope of ∼ 1.6 and a cutoff at lg(LX) ∼ 40.5. The ULX sources found in many starburst galaxies occupy the high luminosity end of this single slope power law distribution, whereas its low luminosity part is composed of " ordinary " high mass X-ray binaries, observed, e.g. in the Milky Way and Magellanic Clouds. As the normalization of the " universal " luminosity function is proportional to the star formation rate, the number and/or the collective X-ray luminosity of HMXBs can be used to measure the current value of SFR in the host galaxy. Distant (unresolved) starburst galaxies observed by Chandra at redshifts of z ∼ 0.2 − 1.3 obey the same LX −SFR relation as local galaxies, indicating that the ULXs at these redshifts were not significantly more luminous than those found in nearby galaxies.