Star-forming and passive galaxies at z ~ 2 in the CFHT Legacy Survey

Abstract

In this work we use the latest results from the four Deep Fields of the Canada France Hawaii Telescope Legacy Survey (CFHTLS) combined with the WIRCam Deep Survey (WIRDs) covering 2 .51 deg [superscript 2] to study the number counts and luminosity functions of z ∼ 2 star-forming and passive galaxies to K[subscript s]<23. To construct our catalogs, we used an adaptation of the BzK[subscript s] selection criteria to the available filters of the CFHTLS: The gzK[subscript s] color-color plot combined with a new infrared zJHK[subscript s] color selection allows us to discriminate between star-forming and passive galaxies at z ∼ 2. We build number counts and luminosity functions for these two different populations in each Deep Field and average fields. Our luminosity function for passive galaxies exhibits a flattening and a possible turnover at K[subscript s] ∼ 22. This turnover is clear in some of the Deep fields but not in all of them and this could imply that this turnover is not universal. From this observation, we conclude that the passive galaxy population at z ∼ 2 is dominated by intermediate-mass objects. Our results are consistent with the downsizing scenario of galaxy evolution in which the most massive systems stop star-formation before less massive ones.