THE ESO NEARBY ABELL CLUSTER SURVEY IV - THE FUNDAMENTAL PLANE OF CLUSTERS OF GALAXIES

We have used the ESO Nearby Abell Cluster Survey (ENACS) in combinatio n with the Cosmos Galaxy Catalogue, to investigate the existence of a Fundamental Plane (FP) for rich clusters of galaxies. The 20 clusters with the most regular projected galaxy distributions appear to define a quite narrow FP, which is similar to the FP found by Schaeffer et al ., who used other clusters. Our cluster FP appears to be different fro m that of ellipticals, as well as from the virial prediction. The latt er fact may have several physical explanations, or a combination there of. If M/L varies with L this will change the FP slope away from the v irial slope. Differences in dynamical structure between clusters will also produce deviations from the virial FP. In view of the long virial ization time-scales in all but the very central parts of galaxy cluste rs, the deviation of the cluster FP from the virial expectation may al so result from clusters not being totally virialized. The scatter of t he observations around the cluster FP is fairly small. An important pa rt of the observed scatter is likely to be intrinsic. If this intrinsi c spread were due exclusively to deviations from the Hubble flow it wo uld imply cluster peculiar velocities of at most about 1000 km s(-1).