The environmental dependence of properties of galaxies around the RDCSJ0910+54 cluster at z=1.1

We report on the environmental dependence of properties of galaxies around the RDCSJ0910+ 54 cluster at z = 1.1. We obtained multi-band wide-field images of the cluster with Suprime-Cam and MOIRCS on Subaru and WFCAM on UKIRT. Also, an intensive spectroscopic campaign was carried out using LRIS on Keck and FOCAS on Subaru. We collected 161 spectra with secure redshifts, with which we calibrated a larger sample of photometric redshifts. We discover a possible large-scale structure around the cluster in the form of three clumps of galaxies. Two out of the three newly discovered clumps of galaxies are detected as extended X-ray sources, suggesting that they are bound systems. There seem to be filaments of galaxies in between the clumps. This is potentially one of the largest structures found so far in the z > 1 Universe. We then examined stellar populations of galaxies in the structure. First, we quantified the color-radius relation. Red galaxies have already become the dominant population in the cores of rich clusters at z similar to 1, and the fraction of red galaxies has not strongly changed since then. The red fraction depends on the richness of clusters in the sense that it is higher in rich clusters than in poor groups. We confirm that this trend is not due to possible biases in photometric redshifts. Next, we examined red sequence galaxies. The luminosity function of red galaxies in rich clusters is consistent with one in local clusters. On the other hand, the luminosity function of red galaxies in poor groups shows a deficit of faint red galaxies. This confirms our earlier findings that galaxies follow an environment-dependent down-sizing evolution. Interestingly, the truncation magnitude of the red sequence appears brighter than found in the RDCS J1252-29 field at z = 1.24. This suggests that there is a large variation in the evolutionary phases of galaxies in groups with similar masses. Further studies of high redshift clusters will be a promising way of addressing the role of nature and nurture effects in shaping the environmental dependence of galaxy properties observed in the local Universe