More extragalactic carbon monoxide

We have detected CO emission toward the centers of six spiral galaxies: NGC 660, 3504, 3628, 4303, 4631, and 4826: which had been predicted to have molecular sources similar to that in the center of our own galaxy on the basis of OH and IR studies. Analysis of the entire sample of galaxies with strong central CO peaks supports the interpretation of the central peaks as components distinct from the disk molecular clouds. We suggest a new method for estimating the mass of associated H2 that emphasizes the different kinds of clouds in these different regions. There appears to be no correlation of CO and H I linewidths. However, there are good correlations between CO emission, far-infrared emission, and nonthermal radio continuum emission. The correlation with infrared emission shows that more molecular gas implies more star formation in galactic centers. The correlation with nonthermal emission suggests the need for a connection between central star-formation activity and the global structural properties of spiral galaxies