Speaker
Description
Ultraluminous X-ray sources (ULX) are thought to be dominated by the most luminous X-ray binaries, many of which accrete at super-Eddington rates, although some small fraction of the population may harbor intermediate-mass black holes. We present a catalog of ULX candidates identified in the first eROSITA all-sky survey (eRASS1) consisting of 89 strong ULX candidates which we use for further analysis and 260 weaker candidates which require confirmation by dedicated X-ray observations. Contrary to earlier works based on serendipitous detections in pointed observations, our catalog was created from the unbiased X-ray observations performed by eROSITA across all galaxies listed in the Heraklion Extragalactic Catalogue of the eROSITA-DE sky. We estimate the number of unknown background contaminants and the sensitivity of our identification procedure, after removing known contaminants such as foreground stars, AGN, and supernovae. We determine the X-ray luminosity function (XLF) of ULX and compare against extrapolations of the XLFs of other populations such as low- and high-mass X-ray binaries. We determine the fraction of ULXs identified in galaxies of different morphological types and find that ULXs with luminosities below 1e41 erg/s are concentrated in late-type galaxies. As for high luminosity ULXs, we identify an excess in early-type galaxies that cannot be attributed to the high mass X-ray binary population but is expected to arise from low-mass X-ray binaries or the elusive intermediate mass black hole population.
