A Cluster, Group, and Subgroup Catalog Using SDSS DR12

Galaxy Clusters with complex inner structures are excellent laboratories with which to study the properties of galaxies and the groups of galaxies in them. To execute a systematic search for flux-limited galaxy groups and clusters based on the spectroscopic galaxies with r < 17.77 of SDSS data release 12, we adopt a modified version of the friends-of-friends algorithm, whereupon a total of 3272 galaxy groups and clusters with at least 10 members are found. In this study, we aim to assign galaxy subgroups within groups and clusters that enable us to investigate the detained star-formation history of galaxies by applying a modified hierarchical grouping method to our galaxy group and cluster catalog. We note that roughly 70% of our galaxy groups and clusters have subgroups. The most remarkable additional results are as follows. The brightest cluster galaxies (BCGs) have brighter luminosities with larger velocity dispersions of groups and clusters. The BCGs are concentrated toward the most massive subgroups than the second and third one. This result implies that the galaxy properties can be affected by different merger and star-formation histories for differing environments.