Seminars at FGG

Do Ultra-luminous X-ray sources prefer metal-poor environments?

Speaker: Emanuele Ripamonti (Dip.di Fisica, Universit√° di Milano-Bicocca)

Date and time: 2011-06-06 10:30

The origin of Ultra-Luminous X-ray sources (i.e. point-like, non-nuclear X-ray sources with LX > 10^39 erg/s), focusing on the promising scenario where such objects can be explained with accretion onto 25-80 Msun "massive stellar black holes" (MSBHs). Since stellar evolution predicts that MSBHs can only form from the direct collapse of moderately metal-poor (Z<~0.3 Zsun) stars, this scenario can be tested by measuring the metallicity around ULXs and/or of in their host galaxies. Data in the literature suggest that this is the case, but the evidence is statistically weak because of the relatively low number (~65) of ULX-hosting galaxies with reliable metallicity determinations. Therefore, we started an observational effort to increase the sample.