Shrinking of Cluster Ellipticals: A Tidal Stripping Explanation and Implications for the Intracluster Light

Abstract

We look for evidence of tidal stripping in elliptical galaxies through the analysis of homogeneous CCD data corresponding to a sample of 228 elliptical galaxies belonging to 24 clusters of galaxies at 0.015 < z < 0.080. We investigate departures from the standard magnitude-isophotal size relation as a function of environmental (clustercentric distance, local galaxy density) and structural (cluster velocity dispersion, Bautz-Morgan type) properties. We find that, for any particular galaxy luminosity, the elliptical galaxies in the inner and denser regions of the clusters are about 5% smaller than those in the outer regions, which is in good agreement with the finding of Strom and Strom based on photographic photometry. The null hypothesis (i.e., galaxy sizes are independent of the clustercentric distance or density) is rejected at a significance level of better than 99.7%. The numerical models of Aguilar and White predict that tidal stripping can lead to changes in the whole structure of elliptical galaxies, producing shrinkage and brightening of the galaxy qualitatively consistent with our measurements and also with the findings of Trujillo and coworkers that more centrally concentrated elliptical galaxies populate denser regions. Our observational results can be interpreted as evidence for the stripping of stars from elliptical galaxies in the central/denser regions of clusters, contributing to the intracluster light observed in these structures.