THE GENESIS OF STARBURSTS AND INFRARED-EMISSION IN THE CENTERS OF GALAXIES

We present 10.8 mum maps of the central regions of 21 infrared-luminou s galaxies. Each map, obtained using the NASA MSFC bolometer array at the IRTF, has a resolution of approximately 4'' and spans typically 25 '' x 20''. Some of the galaxies have also been mapped at 12.5, 19.2, a nd 30 mum. The sample consists primarily of starburst galaxies but inc ludes several Seyferts and LINERs. On average, the flux detected in ea ch map is approximately 58% of that detected at 12 mum by IRAS. We see a variety of morphologies, including compact and elongated sources an d more complex distributions exhibiting such features as kiloparsec-si ze rings and double lobes. The midinfrared radiation is emitted by dus t particles, and for two of the galaxies we see spatial color variatio ns attributable to the presence of very small grains and consistent wi th their depletion in the starbursts. The mid-infrared emission traces the dust heated by the youngest stars. Comparison of the distribution s of intense star formation and the dense neutral interstellar medium for eight of these galaxies demonstrates that the two are intimately l inked. For several of the galaxies, infrared and CO peaks coincide, al though for most of the galaxies the dense gas is much more extended th an the star formation. Our sample contains a preponderance of barred g alaxies. We show for a subset of the sample that the most intense star formation tends to occur in the circumnuclear regions at the inner Li ndblad resonances (ILRs) when ILRs exist or at the nuclei when ILRs do not exist. We interpret these findings by considering how bars and dy namical resonances effect the distribution and properties of gas in ga laxies.