The faint-end slopes of galaxy luminosity functions in the COSMOS field

We examine the faint-end slope of the rest-frame V-band luminosity function (LF), with respect to galaxy spectral type, of field galaxies with redshift z < 0.5, using a sample of 80,820 galaxies with photometric redshifts in the 2 deg(2) Cosmic Evolution Survey (COSMOS) field. For all galaxy spectral types combined, the LF slope ranges from -1.24 to -1.12, from the lowest redshift bin to the highest. In the lowest redshift bin (0.02 < z < 0.1), where the magnitude limit is M-V less than or similar to -13, the slope ranges from similar to -1.1 for galaxies with early-type spectral energy distributions (SEDs) to alpha similar to -1.9 for galaxies with low-extinction starburst SEDs. In each galaxy SED category (early-type, Sbc, Scd+ Irr, and starburst), the faint-end slopes grow shallower with increasing redshift; in the highest redshift bin (0.4 < z < 0.5), alpha similar to -0.5 and -1.3 for early types and starbursts, respectively. The steepness of alpha at lower redshifts could be qualitatively explained by LF evolution, or by large numbers of faint dwarf galaxies, perhaps of low surface brightness, that are not detected at higher redshifts.