The ESO Nearby Abell Cluster Survey. XI. Segregation of cluster galaxies and subclustering

TL;DR

This study analyzes galaxy segregation by luminosity and morphology in 59 nearby clusters, revealing differences in distributions related to substructure presence and galaxy type, with implications for galaxy evolution processes.

Contribution

It provides new insights into how galaxy properties and substructures influence their spatial and velocity distributions within clusters.

Findings

Luminosity segregation observed only for bright ellipticals outside substructure.

Early- and late-type galaxies show distinct segregation patterns.

Galaxies within substructure have different distributions than those outside.

Abstract

We study luminosity and morphology segregation of over 3000 cluster galaxies in an ensemble cluster of 59 rich, nearby galaxy clusters observed in the ESO Nearby Cluster Survey (ENACS). Within this sample we identify those galaxies that are in substructures. We compare the distribution of projected clustercentric distance, R, and 'normalized' relative line-of-sight velocity, v, of several subsamples, using the 2D Kolmogorov-Smirnov test. We find evidence of luminosity segregation only for the ellipticals outside substructure and brighter than M_R = -22.0 +/- 0.1 (h0=100 km/s/Mpc). We confirm the well-known segregation of early- and late-type galaxies. The early and late spirals (Sa--Sb and Sbc--Ir respectively) outside substructure also appear to have different (R,v)-distributions. In each morphological class, the galaxies within substructure have different (R,v)-distributions from the galaxies that are not in substructure. Among the samples of galaxies that are not in substructure, at least 3 ensembles can and must be distinguished: [E+S0], S_early, and [S_late+ELG]. The [E+S0] ensemble is most centrally concentrated and has a fairly low velocity dispersion that hardly varies with radius. The [S_late+ELG] ensemble is least concentrated and has the highest velocity dispersion, which increases significantly towards the centre. The (R,v)-distribution of S_early galaxies is intermediate between those of the two other ensembles. Among the galaxies within substructure the S0 and [S_late+ELG] galaxies have different (R,v) distributions. We discuss briefly the implications of our results for processes of galaxy destruction and transformation within clusters. [ABRIDGED]