The VIMOS VLT Deep Survey. Evolution of the luminosity functions by galaxy type up to z = 1.5 from first epoch data

International audienceFrom first epoch observations of the VIMOS VLT Deep Survey (VVDS) we have derived luminosity functions for galaxy samples selected by spectral type out to z=1.5. With the VVDS we are able to investigate within the same sample the evolution of the type dependent luminosity function selected in several rest-frame bands over 70% of the age of the Universe. The simple I_AB=24 VVDS magnitude limit is significantly fainter than other complete spectroscopic surveys and allows the determination of the faint end slope of the luminosity function with unprecedented accuracy. Galaxies have been classified in four spectral types, from early type to irregular galaxies, using their colours and redshift. Luminosity functions have been computed in the U, B, V, R and I rest frame bands for each type, in redshift bins from z=0.05 to z=1.5. In all the considered rest frame bands, we find a significant steepening of the luminosity function from early to late types. The characteristic luminosity M* of the Schechter function is significantly fainter for late type galaxies and this difference between types increases in the redder bands. For each spectral type we find a brightening of M* with increasing redshift, ranging from &lsim;0.5 mag for early type galaxies to ~1 mag for the latest type galaxies, while the slope of the luminosity function of each spectral type is consistent with being redshift-independent. The luminosity function of early type galaxies is consistent with passive evolution up to z&tilde; 1.1, whilst the number of bright (MB_ABB_AB< -20) late type galaxies in the same redshift range increases of a factor ~6.6. These results indicate a strong type-dependent evolution and identifies the latest spectral types as responsible for most of the evolution of the UV-optical luminosity function out to z=1.5