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Description
One hundred seven ultraluminous X-ray sources (ULXs) with 0.3-10.0keV luminosities in excess of 10^39^erg/s are identified in a complete sample of 127 nearby galaxies. The sample includes all galaxies within 14.5Mpc above the completeness limits of both the Uppsala Galaxy Catalogue (Cat. VII/26) and the Infrared Astronomical Satellite survey (Cat. II/125). The galaxy sample spans all Hubble types, a four-decade range in mass, 7.5<log(M/M_{sun}_)<11.4, and in star formation rate, 0.0002<SFR(M_{sun}_/yr)<=3.6. ULXs are detected in this sample at rates of one per 3.2x10^10^M_{sun}_, one per ~0.5M_{sun}_/yr star formation rate, and one per 57Mpc^3^ corresponding to a luminosity density of ~2x10^37^erg/s/Mpc^3^. At these rates we estimate as many as 19 additional ULXs remain undetected in fainter dwarf galaxies within the survey volume. An estimated 14 objects, or 13%, of the 107 ULX candidates are expected to be background sources. The differential ULX luminosity function shows a power-law slope {alpha}~-0.8 to -2.0 with an exponential cutoff at ~20x10^39^erg/s with precise values depending on the model and on whether the ULX luminosities are estimated from their observed numbers of counts or, for a subset of candidates, from their spectral shapes. Extrapolating the observed luminosity function predicts at most one very luminous ULX, L_X_~10^41^erg/s, within a distance as small as 100Mpc. The luminosity distribution of ULXs within the local universe cannot account for the recent claims of luminosities in excess of 2x10^41^erg/s, requiring a new population class to explain these extreme objects.
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