High-resolution mid-infrared imaging of infrared-luminous starburst galaxies

Observations for seven infrared-luminous starburst galaxies are reported in the mid-infrared from 8 to 18 mum using the Keck telescopes with spatial r esolution approaching the diffraction limit. All of the galaxies observed s how evidence of strong interactions based on optical morphologies. For thes e galaxies, a substantial fraction, usually more than 50%, of the infrared luminosity is generated in regions ranging in sizes from 100 pc to 1 kpc. N uclear starbursts often dominate the infrared luminosity, but this is not a lways true. In some galaxies, most notably NGC 6090, substantial infrared l uminosity greatly in excess of the nuclear luminosity is generated in regio ns associated with the physical interaction between two galaxies. The radio emission is a good tracer of the location of high-luminosity young stars. The visual/ultraviolet radiation output of the nearby star-forming galaxies is dominated by emission from regions that are generally not producing the copious infrared luminosity of the systems. As seen in comparing the mid-i nfrared and near-infrared images of the galaxies observed here, the regions of high-infrared luminosity in local galaxies are significantly smaller th an the galaxies as a whole. The integrated spectral energy distributions (S EDs) of these galaxies are very different from the SEDs of the regions of s tar formation. If the SEDs of star-forming regions in these galaxies reflec t the SEDs that would be found in forming galaxies at high redshift, we wou ld expect the distant galaxies to be dominated by the mid- and far-infrared luminosity output far more than the integrated luminous output of nearby s tarburst galaxies would suggest.