The Large-Scale Environment of Groups & Clusters of Galaxies

Abstract

It appears that the dynamical status of clusters and groups of galaxies is related to the large-scale structure of the Universe. A few interesting trends have been established: (1) The Cluster Substructure - Alignment Connection, by which clusters show a strong correlation between their tendency to be aligned with their neighbors and their dynamical state (as indicated by the existence of significant substructres). (2) The Cluster Dynamics -Cluster Clustering Connection, by which dynamically young clusters are more clustered than the overall cluster population. (3) The Cluster- Supercluster Alignment Connection, by which clusters of galaxies show a statistical significant tendency to be aligned with the projected major axis orientation of their parent supercluster. (4) The Galaxy Alignment - Cluster Dynamics Connection, by which red-sequence cluster bright galaxies show a significant trend to be aligned with their parent cluster major axis, especially in dynamically young clusters. (5) The Group Richness - Shape Connection, by which groups of galaxies are flatter the poorer they are. These are strong indications that clusters develop in a hierarchical fashion by anisotropic merging of smaller units along the large-scale filamentary structures within which they are embedded.

Invited Talk in IAU colloquium 195 (Torino, March 12-16 2004)