QUANTITATIVE MORPHOLOGY OF ISOLATED E/S PAIRS OF GALAXIES

We present a study of the morphology and geometry for 22 southern E + S pair candidates using high resolution CCD frames obtained at the ESO 2.2 m telescope. We find a considerable number of true mixed pairs with approximately 13/11 elliptical + spiral pairs in the present sample. The remaining objects include approximately 3 "disky" pairs (composed of S0 and S members) and 3 "early-type" pairs comprising E and S0 members. We estimate that between 10 and 25% of the pairs in any complete (non-hierarchical) sample will be of the E + S type. This suggests that morphological concordance is not the rule among paired galaxies. We suggest that interaction phenomena and the alterations they produce in galaxy forms may explain many of the mixed pairs. Eight early-type components show possible shell structure while 78% show an isophotal twisting of greater than 10-degrees. Three of these objects and two additional pairs may be mergers in progress based upon their chaotic morphologies. We suggest that the early-type components in many pairs could be merger products. These E + S pairs might then be a transient stage in the coalescence of compact groups. As many as six of the later type components in our sample show arm-like features that may have been produced by the interaction phenomenon. Some of these objects may have been lenticulars perturbed into pseudo spiral forms. Thus many E + S pairs may not have had an origin as morphologically discordant systems.