Galaxy associations within the Coma cluster

The mean redshift of the core of the Coma cluster - cz = 6953 km s(-1) and its dispersion sigma = 949 km s(-1) are obtained by means of the analysis of the substructures of this cluster by using the S-tree method. The existence of three subgroups of galaxies is revealed, one of them is associated with the cD galaxy NGC 4874, the other - with NGC 4889. It is argued that these subgroups are galaxy associations, i.e. galactic dynamical entities moving within the main cluster. Thus, we conclude that the non-stationarity of the dynamical processes ongoing in the Coma core is due to the merging of small-scale galaxy associations, rather than of two equal sized clusters. We provide the lists of the galaxies of the associations, the observational study of which can be of particular interest. (C) 2001 Published by Elsevier Science B.V.