COMPARATIVE-STUDY OF FINE-STRUCTURE IN SAMPLES OF ISOLATED AND PAIREDEARLY-TYPE GALAXIES

Fine structure in early-type galaxies is considered to be among the mo re robust indicators of a past merging or acquisition event, although growing evidence from numerical simulations suggests that fine structu re may be also interpreted in a 'weak interaction' framework. We prese nt a morphological study of a sample composed of 61 'isolated' early-t ype galaxies addressed to the detection of fine structure. This sample has been selected in order to be statistically comparable to a set of 54 early-type galaxies, members of pairs analysed by Reduzzi & Rampaz zo with a similar technique. The rate of occurrence of fine structure detected in the 'isolated' galaxy sample is significantly higher than that found for the pairs. In particular, the fraction of isolated earl y-type galaxies exhibiting shells is 16.4 per cent, a percentage simil ar to that found by Malin & Carter for RC2 isolated objects in the sou thern sky, while the fraction of early-type galaxies in pairs is appro ximate to 4 per cent. We discuss the comparison between the two sample s in the context of the merger versus the weak interaction origin of f ine structures. Concerning the formation of shells, although the merge r origin cannot be ruled out, the observed difference is more naturall y explained within the weak interaction framework.