The components of mid- and far-infrared emission from S0 and early-type shell galaxies

We have used the Infrared Astronomical Satellite (IRAS) database to search for detections of about 150 early-type (elliptical and S0) galaxies that exhibit shell structure. This morphology is widely believed to be the consequence of a low-velocity merger between galaxies. If so, an increased rate of star formation or other heating of the interstellar medium may be expected. We find no strong evidence for the enhancement of either process in the majority of our sample. Most of the shell galaxies in our sample that are detected by IRAS appear to be otherwise-normal S0's, although we emphasize the uncertain morphological classification for many of these objects. Shell structure is a product of interactions between stars and apparently will be maintained for at least a few times 10^8^ yr. Although the interstellar gas presumably participates in the interaction, heating of a major fraction of its total mass may not be sustained for this length of time. S0 galaxies are commonly detected by IRAS, and the infrared emission from the majority of our sample of shell galaxies appears to be no different from that in normal S0's. Much of this emission may be related to star formation and a warm interstellar medium that exists independently of an interaction with another galaxy. However, for some of the galaxies in our sample, either a contribution from warm dust surrounding evolved stars or, perhaps more likely, emission from an active nucleus may be significant. Thus, the infrared emission from S0 galaxies may not be, without additional information, a good measure of either the star-formation rate or the nonnuclear mass of the cool interstellar medium.