HIGH-RESOLUTION MIDINFRARED IMAGING OF INFRARED-LUMINOUS GALAXIES

We present high-resolution mid-infrared (similar to 10 mu m) imaging o f a flux-limited sample of galaxies with far-infrared luminosity L(FIR ) > 10(11) L(.). This work was done to investigate whether the energy generation mechanism powering these infrared-luminous galaxies comes f rom massive bursts of star formation or from active galactic nuclei (A GNs). Our images trace the spatial extent of the warm (greater than or similar to 200 K) dust, which must lie close to the heating source. T he majority of the sample galaxies are extended, which implies a starb urst as the source of at least part of the energy. However, most of th e galaxies also contain an unresolved nucleus, so the presence of an A GN cannot be ruled out. We argue that the observations are consistent with an evolutionary model in which the infrared-luminous galaxies are seen as dusty cocoons for the birth of quasars.