Keck mid-IR High-Resolution Imaging of Arp 220

To identify the main power source of an object, it is necessary to obtain high-resolution images of that object at the wavelengths at which most of the luminosity is coming out. However, such observations had not been possible in the studies of ULIRGs, which release most of their luminosity in the mid/far-IR. High-resolution imaging at 25 µm, for example, requires not only a sensitive mid-IR camera but also a 10-m class telescope to achieve a sub-arcsecond difraction limit. Recently, such high-resolution imaging in the mid-IR has become possible with the MIRLIN mid-IR camera (Ressler 1994) on the Keck II telescope. This camera is based on a 128 x 128 Si:As array, and has a field of view of 17" on a side with a pixel scale of 0."138/pixel. The working wavelength range is 5-26 µm. Using MIRLIN, we are now undertaking a program to perform high-resolution mid-IR imaging of nearby ultraluminous IR galaxies. Here, we present our first results on Arp 220. More details can be found in Soifer et al. (1999).