Xi. Segregation of Cluster Galaxies and Subclustering

We study luminosity and morphology segregation of cluster galaxies in an ensemble cluster built from 59 rich, nearby galaxy clusters observed in the ESO Nearby Cluster Survey (ENACS). The ensemble cluster contains 3056 member galaxies with positions, velocities and magnitudes ; 96% of these also have galaxy types. From positions and velocities we identify galaxies within substruc-tures, viz. as members of groups that are significantly colder than their parent cluster, or whose average velocity differs significantly from the mean. We compare distributions of projected clustercentric distance R and relative line-of-sight velocity v, of galaxy sub-samples drawn from the ensemble cluster, to study various kinds of segregation, the significance of which is obtained from a 2-dimensional Kolmogorov-Smirnov test. We find that luminosity segregation is evident only for the ellipti-cals that are outside (i.e. not in) substructure and which are brighter than M R = −22.0 ± 0.1. This is mainly due to the brightest cluster members at rest at the centre of the cluster potential. We confirm the well-known segregation of early-and late-type galaxies. For the galaxies with M R > −22.0 of all types (E, S0, S and emission-line galaxies, or ELG, for short), we find that those within substructure have (R, v)-distributions that differ from those of the galaxies that are not in substructure. The early and late spirals (Sa– Sb and Sbc–Ir respectively) that are not in substructure also appear to have different (R, v)-distributions. For these reasons we have studied the segregation properties of 10 galaxy subsamples: viz. E, S0, S e , S l and ELG, both within substructure and outside substructure. Among the 5 samples of galaxies that are not in substruc-ture, at least 3 ensembles can and must be distinguished; these are: [E+S0], S e , and [S l +ELG]. The [E+S0] ensemble is most centrally concentrated and has a fairly low velocity dispersion that hardly varies with radius. The [S l +ELG] ensemble is least concentrated and has the highest velocity dispersion, which increases significantly towards the centre. The class of the S e galaxies is intermediate to the two ensembles. Its velocity dispersion is very similar to that of the [E+S0] galaxies in the outer regions but increases towards the centre. The galaxies within substructure do not all have identical (R, v)-distributions; we need to distinguish at least two ensembles, because the S0 and [S l +ELG] galaxies have different distributions in …