Distribution and evolution of galaxy groups in the Ursa Major supercluster

Abstract

We study an SDSS sample of galaxies within 50 Mpc of the nominal center of the Ursa Major supercluster. Our aim is to study galaxy distribution around groups in the supercluster and the link between the distribution of relaxed and nonrelaxed galaxy systems with respect to the supercluster environment. Using the FoF algorithm, 40 galaxy groups were identified in this region. We classified the systems according to the results of normality and substructure tests applied to member galaxies. Then, we studied the relative distribution of relaxed and nonrelaxed systems across the supercluster. We find that 68% of galaxy groups are Gaussian and that all the non-Gaussian systems have substructures and probably correspond to multimodal systems in redshift space. We also find that the Gaussian systems inhabit the denser regions of the supercluster, with higher densities of both red and blue galaxies within 2.5 Mpc, and have smaller group-group pairwise separations. Our results suggest a spatial segregation of dynamical states, where relaxed systems may have formed and evolved earlier and faster around high-density peaks, while nonrelaxed systems may be growing slower on the peripheries of lower density peaks. In this picture, galaxy clustering seems to be prompting a continuous internal evolution in the supercluster, with several groups collapsing into the more evolved and contracted regions.