  Infrared emission has been detected from normal elliptical galaxies and from
clusters of galaxies at 60um and 100um with the IRAS satellite. In both cases,
the emission has the characteristics of cool dust with a temperature near 30K.
For the elliptical galaxies, there is a correlation between the optical
luminosities and the far infrared luminosities. The likely source of the dust
in these systems is mass loss from stars, which is heated by starlight and
either is distributed throughout the galaxy or falls into a central disk.
Analysis of upcoming ISO data will permit us to distinguish between these
possibilities.
  The far infrared emission from clusters of galaxies is of high luminosity but
is only detected in 10% of the cases. The heating is either due to electron
impact from the hot gas (a suitable explanation for one cluster) or photon
absorption. The source of the dust is probably gas stripped from galaxies. For
clusters, ISO data will provide good mass determinations and positions, thereby
allowing us to determine the source of the heating.
