We study the evolution of galaxy populations around the spectroscopic WiggleZ sample of starforming galaxies at 0.25 < z < 0.75 using the photometric catalog from the Second Red-Sequence Cluster Survey (RCS2). We probe the optical photometric propert
ies of the net excess neighbor galaxies. The key concept is that the marker galaxies and their neighbors are located at the same redshift, providing a sample of galaxies representing a complete census of galaxies in the neighborhood of star-forming galaxies. The results are compared with those using the RCS WiggleZ Spare-Fibre (RCS-WSF) sample as markers, representing galaxies in cluster environments at 0.25 < z < 0.45. By analyzing the stacked color-color properties of the WiggleZ neighbor galaxies, we find that their optical colors are not a strong function of indicators of star-forming activities such as EW([OII]) or GALEX NUV luminoisty of the markers. The galaxies around the WiggleZ markers exhibit a bimodal distribution on the color-magnitude diagram, with most of them located in the blue cloud. The optical galaxy luminosity functions (GLF) of the blue neighbor galaxies have a faint-end slope alpha of sim -1.3, similar to that for galaxies in cluster environments drawn from the RCS-WSF sample. The faint-end slope of the GLF for the red neighbors, however, is sim -0.4, significantly shallower than the sim -0.7 found for those in cluster environments. This suggests that the build-up of the faint-end of the red sequence in cluster environments is in a significantly more advanced stage than that in the star-forming and lower galaxy density WiggleZ neighborhoods. We find that the red galaxy fraction (fred) around the star-forming WiggleZ galaxies has similar values from z sim 0.3 to z sim 0.6 with fred sim 0.28, but drops to fred sim 0.20 at z > sim0.7. This change of fred with redshift suggests that (and more...)
Using wide-field $BVR_cI$ imaging for a sample of 16 intermediate redshift ($0.17 < z < 0.55$) galaxy clusters from the Canadian Network for Observational Cosmology (CNOC1) Survey, we investigate the dependence of cluster galaxy populations and their
evolution on environment. Galaxy photometric redshifts are estimated using an empirical photometric redshift technique and galaxy groups are identified using a modified friends-of-friends algorithm in photometric redshift space.We utilize the red galaxy fraction (fred) to infer the evolutionary status of galaxies in clusters, using both individual galaxies and galaxies in groups. We apply the local galaxy density, sig5, derived using the fifth nearest-neighbor distance, as a measure of local environment, and the cluster-centric radius, rCL, as a proxy for global cluster environment. Our cluster sample exhibits a Butcher-Oemler effect in both luminosity-selected and stellar-mass-selected samples. We find that fred depends strongly on sig5 and rCL, and the Butcher-Oemler effect is observed in all sig5 and rCL bins. However, when the cluster galaxies are separated into rCL bins, or into group and non-group subsamples, the dependence on local galaxy density becomes much weaker. This suggests that the properties of the dark matter halo in which the galaxy resides have a dominant effect on its galaxy population and evolutionary history. We find that our data are consistent with the scenario that cluster galaxies situated in successively richer groups (i.e., more massive dark matter halos) reach a high fred value at earlier redshifts. Associated with this, we observe a clear signature of `pre-processing, in which ... <and more>
