The CNOC2 Field Galaxy Luminosity Function. I. A Description of Luminosity Function Evolution

We examine the evolution of the galaxy luminosity function (LF) using a sample of over 2000 galaxies, with 0.12<z<0.55 and 17.0<R_C<21.5, drawn from the Canadian Network for Observational Cosmology Field Galaxy Redshift Survey (CNOC2), at present the largest such sample at intermediate redshifts. We use UBVR_CI_C photometry and the spectral energy distributions (SEDs) of Coleman, Wu, and Weedman to classify our galaxies into early, intermediate, and late types, for which we compute LFs in the rest-frame B, R_C, and U bandpasses. In particular, we adopt a convenient parameterization of LF evolution including luminosity and number density evolution and take care to quantify correlations among our LF evolution parameters. We also carefully measure and account for sample selection effects as functions of galaxy magnitude and color.

Our principal result is a clear quantitative separation of luminosity and density evolution for different galaxy populations and the finding that the character of the LF evolution is strongly dependent on galaxy type. Specifically, we find that the early- and intermediate-type LFs show primarily brightening at higher redshifts and only modest density evolution, whereas the late-type LF is best fit by strong number density increases at higher z with little luminosity evolution. We also confirm the trend seen in previous smaller z<~1 samples of the contrast between the strongly increasing luminosity density of late-type galaxies and the relatively constant luminosity density of early-type objects. Specific comparisons against the Canada-France and Autofib redshift surveys show general agreement among our LF evolution results, although there remain some detailed discrepancies. In addition, we use our number count and color distribution data to further confirm the validity of our LF evolution models to z~0.75, and we also show that our results are not significantly affected by potential systematic effects such as surface brightness selection, photometric errors, or redshift incompleteness.