Program: GS-2005B-Q-30

Most scenarios for the formation of super-massive black holes require the presence of massive (~ few hundred solar mass) black holes in the early universe, formed by the collapse of primordial Population III stars. It is predicted that a relic of this population could still be present in galactic halos at the current epoch. However, to date no CONCLUSIVE evidence for a class of intermediate-mass black holes has been found. The most promising candidates are the ultraluminous X-ray sources (ULXs), which show tantalising X-ray evidence for IMBHs. However, the derivation of a mass function for an ULX is necessary to provide undisputed evidence for (or against) the presence of an IMBH. Here, we propose a 3-hr pathfinder observation of the isolated counterpart to NGC 1313 X-2, to determine whether sufficiently strong stellar emission/absorption features are evident in its UV/optical spectrum for future observations to constrain the compact object mass.