UV excess galaxies: Wolf-Rayet galaxies

We discuss V- and R-band photometry for 67% of the recent SA 57 ultraviolet-selected galaxy sample of M. Sullivan and collaborators. In a sample of 176 W-selected galaxies, Sullivan et al. find that 24% have (UV -B) colors too blue for consistency with starburst spectral synthesis models. We propose that these extreme blue, UV excess galaxies are Wolf-Rayet (W-R) galaxies, starburst galaxies with strong UV emission from W-R stars. We measure a median (V-R) = 0.38 +/- 0.06 for the UV-selected sample, bluer than a sample optically selected at R but consistent with starburst and W-R galaxy colors. We demonstrate that redshifted W-R emission lines can double or triple the flux through the UV bandpass at high redshifts. Thus, the (UV-B) color of a WR galaxy can be up to 1.3 mag bluer at high redshift, and the expected selection function is skewed to larger redshifts. The redshift distribution of the extreme blue, UV excess galaxies matches the selection function we predict from the properties of W-R galaxies.