2003AJ....125..555D

We present Hα and ISO mid- and far-IR observations for a sample of mixed-morphology galaxy pairs that reveal both the stellar and nonstellar signatures of the interaction process. A mixed-morphology pair is perhaps the simplest form of galaxy-galaxy interaction because it is expected to involve only a single rapidly rotating gas-rich component paired with a gas-poor elliptical or lenticular galaxy. A primary assumption that we address is whether spirals are the only IR emitter in these mixed (E+S) pairs. Our observations reveal that many of the early-type galaxies exhibit weak (low equivalent width) emission, as often observed in field elliptical galaxies. These are the classical mixed-morphology pairs. However, some of the early-type components, especially the lenticular galaxies, show evidence for significant star formation, with Hα equivalent widths and 15 µm luminosities comparable to or exceeding those of their often much larger spiral companions. Our sample contains five Seyfert 2 nuclei, of which three can be described as companions on the end of a spiral arm. The Seyfert nucleus is often accompanied by a starburst region, while other such companions currently show only the starburst component. These pairs are among the best candidates for direct interaction fuelling of both starbursts and active galactic nuclei.