On the association of Hickson compact groups with loose groups.
Abstract (from CDS):
Counts of galaxies are made in the vicinity of Hickson compact groups (HCGs). Loose group galaxies are detected in ∼70% of nearby groups with z<0.025. It is shown that members of the loose group associated with a certain HCG are located in a relatively narrow strip oriented along the elongation of the HCG. Such a peculiar distribution of the loose group galaxies and the found correlation of the radial velocity dispersion of the loose group galaxies with the elongation of the group allows us to conclude that the loose group galaxies are rotating around a common gravitational center. This is a clue for the solution of the known puzzles related to HCGs: the lack of strong radio and luminous far-infrared sources, a surprisingly large spiral fraction, the lack of blue elliptical galaxies, and so on. Only those of such elongated formations in which the bright members happen to be oriented close to each other on the sky are detected as compact groups.