HIGH-SPATIAL-RESOLUTION KAO FAR-INFRARED OBSERVATIONS OF THE CENTRAL REGIONS OF INFRARED-BRIGHT GALAXIES

We present new high spatial resolution Kuiper Airborne Observatory (KA O) 50 mu m and/or 100 mu m data for 11 infrared-bright galaxies. The s izes of the central far-infrared-emitting regions in three of these ga laxies, NGC 660, NGC 891, and M83, agree with those of the central sta r formation complexes. The Sb galaxy NGC 7331, which does not have obs erved star formation in its bulge, has a hat-topped 100 mu m major axi s profile that covers the bulge and inner spiral arms, without a brigh t central peak or pronounced depression. The remaining seven galaxies, all of which are known to have strong nuclear or circumnuclear star f ormation, are unresolved or marginally resolved with the KAO, with far -infrared source size limits consistent with the sizes of the central star formation complexes. Along with these new data, we have tabulated previously published KAO data for 11 other galaxies and IRAS 60 and 1 00 mu m data for the bulges of the large angular size galaxies M31 and M81. From the literature, we have compiled optical, near-infrared, an d millimeter measurements for the central regions of the entire set of 24 galaxies. We have used this data set to investigate dust heating a nd star formation in the central areas of galaxies. We find that L(FIR )/L(B) and L(FIR)/L(H) correlate with CO (1-0) intensity and 100 mu m optical depth. Galaxies with optical or near-infrared signatures of OB star formation in their central regions have higher values of I(CO) a nd tau(100) than more quiescent galaxies, as well as higher far-infrar ed surface brightnesses and L(FIR)/L(B) and L(FIR)/L(H) ratios. The L( FIR)/L(H alpha) ratio does not correlate strongly with CO and tau(100) . These data are consistent with a scenario in which OB stars dominate dust heating in the more active galaxies and older stars are importan t for the more quiescent bulges. Whether or not a galaxy bulge has str ong star formation may be decided by a threshold effect; star-forming galaxies have surface gas densities above the Kennicutt critical densi ty, while quiescent galaxies have lower values.