The structure of infrared-luminous galaxies at 100 microns

We have observed 22 galaxies at 100 mum with the Kuiper Airborne Observatory in order to determine the angular size of their FIR-emitting regions. This one-dimensional array data constitutes the highest spatial resolution ever achieved on luminous galaxies in the far-infrared. Most of these galaxies are very luminous far-infrared sources, with L(FIR) > 10(11) L.. We clearly resolved six of these galaxies at 100 mum and have some evidence for extension in seven others. Those galaxies that we have resolved can have little of their 100 pm flux directly emitted by a pointlike active galactic nucleus. Dust heated to similar to 40 K by recent bursts of nonnuclear star formation provides the best explanation for their extreme FIR luminosity. In a few cases, heating of an extended region by a compact central source is also a plausible option.