Spitzer Mid-Infrared Imaging of Nearby Ultraluminous Infrared Galaxies
  We have observed 14 nearby (z<0.16) Ultraluminous Infrared Galaxies (ULIRGs) with Spitzer at 3.6-24 microns. The underlying host galaxies are well-detected, in addition to the luminous nuclear cores. While the spatial resolution of Spitzer is poor, the great sensitivity of the data reveals the underlying galaxy merger remnant, and provides the first look at off-nuclear mid-infrared activity. 
J.A. Surace, Z. Wang, S. Willner, H. Smith, J. Pipher, W. Forrest, G.   Fazio