A Correlation between Light Concentration and Cluster Local Density for Elliptical Galaxies

Using photometric and redshift data for the Virgo and Coma clusters, we present evidence for a correlation between the light concentration of elliptical galaxies (including dwarf ellipticals) and the local 3–D (i.e. non–projected) density of the clusters: more concentrated ellipticals are located in denser regions. The null hypothesis (i.e. the absence of any relation) is rejected at a significance level better than 99.9%. In order to explain the observed relation, a power law relating the galaxy light concentration and the cluster 3–D density is proposed. We study how the projection effects affect the form and dispersion of the data–points in the light concentration– projected density diagram. The agreement between our model and the observed data suggests that there is a paucity of dwarf elliptical galaxies in the cluster central regions. Subject headings: galaxies: clusters: general — galaxies: interactions — galaxies: structure — galaxies: photometry — galaxies: fundamental parameters