The X-Ray Binary Population in M33. I. Source List and Luminosity Function

In this paper we present the source list for three Chandra observations of the Local Group galaxy M33. The observations are centered on the nucleus and on the star-forming region NGC 604. We detect a total of 261 sources in an area of ~0.2 deg2 down to a flux limit of 3 × 10-16 ergs s-1 cm-2, which corresponds to a luminosity of ~2 × 1034 ergs s-1 at a distance of 840 kpc. From the source list we construct the luminosity functions of sources observed in M33. If we take into account background contamination, the luminosity functions are consistent with those of other star-forming galaxies. In addition, the combination of X-ray color analysis and the existence of "blue" optical counterparts strongly indicates that the X-ray point-source population in M33 consists of young objects. Above 3 × 1035 ergs s-1 there are few X-ray sources in the locus of the X-ray hardness ratio diagram that is generally populated by low-mass X-ray binaries.