Outskirts of galaxy clusters: intense life in the suburbs
- M Plionis
- Proceedings IAU Colloquium No. 195
Aims. We study the morphology of galaxy populations of the richest superclusters from the catalogue of superclusters of galaxies in the 2dF Galaxy Redshift Survey. Methods. We use the luminosity density distribution and Minkowski functional V3 to study substructures in superclusters as formed by different populations of galaxies. We compare the properties of grouped and isolated galaxies in regions of different density in superclusters. Results. In high-density cores of rich superclusters there is an excess of early type, passive galaxies, among galaxies in groups and clusters, as well as among those which do not belong to groups, while in lower density outer regions there are more blue, star-forming galaxies both in groups and among those galaxies which do not belong to groups. This also shows that the galaxy content of groups depends on the environment where the groups reside in. The density distributions and the behaviour of the Minkowski functional V3 for different superclusters show that substructures in superclusters as traced by different populations of galaxies are very different. Conclusions. We show how the Minkowski functional V3 can be used to study substructures in superclusters. Both local (group/cluster) and global (supercluster) environments are important in forming galaxy morphologies and star formation activity. Our study shows large differences between individual very rich superclusters, which cannot be solely due to selection effects. They indicate that there are differences in their formation times and evolution stages. The presence of a high density core with X-ray clusters and a relatively small fraction of star-forming galaxies in the supercluster SCL126 may be an indication that this supercluster has started its evolution earlier than the supercluster SCL9.