Wolter, AnnaAnnaWolter0000-0001-5840-9835Fruscione, A.A.FruscioneMapelli, M.M.Mapelli2020-09-102020-09-102017http://hdl.handle.net/20.500.12386/27275Collisional Ring Galaxies (RiGs), with their expanding ring of gas and stars and their high star formation rate are unique objects where to study the most massive products of star formation and shed some light on the nature of ultra luminous X-ray sources (ULXs) found on their rings. We have recently constructed the X-ray luminosity function of ULXs in RiGs which is mostly consistent with previous results but shows two bright objects at the highest luminosity above the extrapolation of previous models for ULXs. They could be the best cases of Intermediate Mass Black Holes, or further ULXs powered by neutron stars, or even something different (e.g Supernovae). We will describe in detail the RiGs and their properties and compare the derived XLF with previous results.ELETTRONICOenMultimediahttps://www.cosmos.esa.int/web/xmm-newton/2017-symposium2017xru..conf..239WFIS/05 - ASTRONOMIA E ASTROFISICA