THE WiggleZ DARK ENERGY SURVEY: GALAXY EVOLUTION AT 0.25 ⩽ z ⩽ 0.75 USING THE SECOND RED-SEQUENCE CLUSTER SURVEY

We study the evolution of galaxy populations around the spectroscopic WiggleZ sample of star-forming galaxies at 0.25 ≤ z ≤ 0.75 using the photometric catalog from the Second Red-Sequence Cluster Survey (RCS2). We probe the optical photometric properties 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([O II]) or Galaxy Evolution Explorer (GALEX) near-UV luminosity 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 (GLFs) of the blue neighbor galaxies have a faint-end slope α of ~ –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 ~ –0.4, significantly shallower than the ~ –0.7 found for those in cluster environments. This suggests that the buildup 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 (f_red) around the star-forming WiggleZ galaxies has similar values from z ~ 0.3 to z ~ 0.6 with f_red ~ 0.28, but drops to f_red ~ 0.20 at z gsim 0.7. This change of f_red with redshift suggests that there is either a higher rate of star-forming galaxies entering the luminosity-limited sample at z ≳ 0.7, or a decrease in the quenching rate of star formation at that redshift. Comparing to that in a dense cluster environment, the f_red of the WiggleZ neighbors is both considerably smaller and has a more moderate change with redshift, pointing to the stronger and more prevalent environmental influences on galaxy evolution in high-density regions.