  Images of Arp 220 from 3.45 to 24.5 $\mu$m with 0.5'' resolution are
presented which clearly separate the nucleus into at least two components. The
western component is about three times more luminous than the eastern
component, but the silicate absorption in the fainter, eastern component is
roughly 50% greater than the absorption in the western component. Each
component is marginally resolved. The two components seen at 24.5 $\mu$m are
identified with the two radio components. The western source most likely
coincides with the high extinction disk previously suggested to exist in Arp
220, while the eastern nucleus is identified with a faint highly reddened
source seen in HST 2.2 $\mu$m NICMOS images. The two nuclei together account
for essentially all of the measured 24.5 $\mu$m flux density. Two models are
presented, both of which fit the observations. In one, the majority of the
total luminosity is produced in an extended star formation region and in the
other most of the luminosity is produced in the compact but extincted regions
associated with the two nuclei seen at 24.5 $\mu$m. In both pictures,
substantial luminosity at 100 $\mu$m emerges from a component having a diameter
of 2--3'' ($\sim$1kpc).

Astrophysics