The Effects of Interactions on the Structure and Morphology of Elliptical/Lenticular Galaxies in Pairs

We present a photometric and structural analysis of 42 E/S0 galaxies in (E/S0+ S) pairs observed in the BVRI color bands. We empirically determine theeffects of interactions on their morphology, structure and stellar populationsas seen from the light concentration (C), asymmetry (A), and clumpiness (S)parameters. We further compare these values to a control sample of 67 mostlyisolated, non-interacting E/S0 galaxies. The paired E/S0 galaxies occupy a morescattered loci in CAS space than non-interacting E/S0's, and the structuraleffects of interactions on E/S0's are minor, in contrast to disk galaxiesinvolved in interactions. This suggests that observational methods forrecognizing interactions at high z, such the CAS methodology, would hardlydetect E/S0's involved in interactions (related to early phases of the socalled `dry-mergers'). We however find statistical differences in A whencomparing isolated and interacting E/S0s. In the mean, paired E/S0 galaxieshave A values 2.96+-0.72 times larger than the ones of non-interacting E/S0's.For the subset of presumably strongly interacting E/S0's, A and S can beseveral times larger than the typical values of the isolated E/S0's. We showthat the asymmetries are consistent with several internal and externalmorphological distortions. We conclude that the interacting E/S0s in pairsshould be dense, gas poor galaxies in systems spaning a wide range ofinteraction stages, with typical merging timescales >~ 0.1-0.5 Gyr. We use theobserved phenomenology of these galaxies to predict the approximate loci of`dry pre-mergers' in the CAS space.(Abridged)Comment: 23 pages, 9 figures included. To appear in The Astronomical Journa