X-ray binaries (XRB) and their most extreme manifestation Ultra-luminous X-ray sources (ULXs), are the dominant source of the hard X-ray emission in star-forming galaxies. X-ray scaling relations between the luminosity of the XRB population and the star-formation rate (SFR) and stellar mass (M∗) have served as an important tool for measuring the XRB component of any galaxy in the local Universe. Moreover, they have been used to set observational constrains to the population synthesis models of XRBs and their formation and evolution parameters.
In this thesis, we have strived to answer the question of whether these correlations are universal and representative of galaxies in the local Universe irrelevant of their conditions (e.g. SFR, M∗). For this reason we test the scaling relations of XRBs on one of the most extreme, highly star-forming galaxies Arp 299 and explore their validity at sub-galactic scales for the ULX-rich galaxies NGC 3310 and NGC 2276 using Chandra data.
Moreover, using the XMM-Newton archive we build the largest X-ray sample of bona-fide normal galaxies observed in the X-ray band (650 objects). This sample is drawn from a complete sample of galaxies within 200Mpc and it encompasses the full range of SFR and M∗ observed in the local Universe. With this sample of local star-forming galaxies, we measure the XRB-SFR and XRB-M∗ scaling relations and their intrinsic scatter. We find that the X-ray luminosity-SFR scaling relation for the full sample of normal local galaxies is sub-linear. This is most likely the result of contribution from ULX-hosting galaxies and/or LMXBs in the low SFR regime. On the other hand the X-ray luminosity-SFR-M∗ scaling relation, is consistent with the relations reported for smaller samples, but with larger intrinsic scatter. The increased scatter is interpreted as the result of the wider range of different types of galaxies (i.e. stellar population ages, metallicity) covered by the full sample in comparison to the previous smaller scale surveys.