Ultra-Luminous X-ray Sources in the Most Metal Poor galaxies

There is growing observational and theoretical evidence to suggest that Ultra-Luminous X-ray sources (ULX) form preferentially in low metallicity environments. Here we report on a Chandra Large Project to survey 25 nearby (< 30Mpc) star forming Extremely Metal Poor Galaxies (Z<5% solar) with both Chandra and HST. Our goals are (1) to determine whether ULX are preferentially found in low metallicity systems (2) test population synthesis models for ULX formation and (3) use the Hubble imaging to determine the ages of the stars clusters in XMPG and hence infer the ages of nearby ULX. Preliminary results indicate that ULX may be preferentially formed in the XMPG sample. For the extremely metal poor galaxies we find that the ratio of the number of ULX to the star formation rate (N_ulx/SFR) is 7.7. In contrast, for a sample of 21 SINGS galaxies with approximately solar metallicity N_ulx/SFR=0.57. We discuss these results in the context of population synthesis models.