  Ultraluminous X-ray sources (ULXs) are some of the most enigmatic X-ray
bright sources known to date. It is generally accepted that they cannot host
black holes as large as those associated with active galaxies, but they appear
to be significantly more luminous than their better understood Galactic X-ray
binary (XRB) cousins, while displaying an intriguing combination of differences
and similarities with them. Through studying large, representative samples of
these sources we may hope to enhance our understanding of them. To this end, we
derive a large catalogue of 650 X-ray detections of 470 ULX candidates, located
in 238 nearby galaxies, by cross correlating the 2XMM Serendipitous Survey with
the Third Reference Catalogue of Bright Galaxies. The presented dedicated
catalogue offers a significant improvement over those previously published both
in terms of number and the contribution of background contaminants, e.g.
distant quasars, which we estimate to be at most 24 per cent, but more likely
~17 per cent. To undertake population studies, we define a `complete'
sub-sample of sources compiled from observations of galaxies with sensitivity
limits below 10^39 erg/s. The luminosity function of this sample is consistent
with a simple power-law. Although we do not find any statistical requirement
for a high luminosity cut-off, as has been reported previously, we are not able
to rule out its presence. Also, we find that the number of ULXs per unit galaxy
mass decreases with increasing galaxy mass for ULXs associated with spiral
galaxies, in broad agreement with previous results, but is consistent with
being constant with galaxy mass for sources associated with elliptical
galaxies.
