HMXB, ULX and star formation
Abstract
Based on recent X-ray observations of the Milky Way, Magellanic Clouds and nearby starburst galaxies we study the population of high-mass X-ray binaries (HMXBs), their connection with ultra-luminous X-ray sources (ULXs) and the relation to the star formation rate (SFR). Although more subtle SFR-dependent effects are likely to exist, the data in the log(LX)~ 36-40.5 luminosity range are broadly consistent with the existence of a ``universal'' luminosity function of HMXBs, which can be roughly described as a power law with a differential slope of ~ 1.6 and a cutoff at log(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 the 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.- Publication:
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Nuclear Physics B Proceedings Supplements
- Pub Date:
- June 2004
- DOI:
- 10.1016/j.nuclphysbps.2004.04.065
- arXiv:
- arXiv:astro-ph/0309725
- Bibcode:
- 2004NuPhS.132..369G
- Keywords:
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- Astrophysics
- E-Print:
- To appear in Proc. of the BeppoSAX Symposium: "The Restless High-Energy Universe", E.P.J. van den Heuvel, J.J.M. in 't Zand, and R.A.M.J. Wijers (Eds)