Annu. Rev. Astron. Astrophys. 1991. 29: 581-625 Copyright © 1991 by Annual Reviews. All rights reserved

3.2 Barred Spiral Galaxies

Optically barred spiral galaxies in which the distribution of molecular matter has been mapped include NGC 5236 (M83) (Combes et al 1978, Lord 1987), NGC 1097 (Gerin et al 1988), and NGC 1365 (Sandquist et al 1988). In all cases, the CO emission is clearly enhanced along the bar. High resolution mapping of CO in NGC 253 has also shown the molecular gas strongly concentrated along the central bar seen in the near infrared (Canzian et al 1988). In the barred spiral galaxy NGC 3351, a nuclear molecular gas bar is found perpendicular to the optical bar (Devereux et al 1991). Several galaxies that do not show obvious barred morphology in the optical have been found to exhibit elongated CO distributions in their centers. High resolution CO observations of IC 342 and NGC 6946 indicate that both of these galaxies have a CO bar in the central arcminute (Lo et al 1984, Ball et al 1985). In IC 342, the CO has been resolved into two offset ridges along the leading edges of the rotating bar (Ishizuki et al 1990). These studies support the theoretical prediction that the bar may promote the inward transfer of gas to the center of the galaxy, thus fueling a central burst of star formation (Sanders & Huntley 1976, Roberts et al 1979).