The radial distribution of the CO emissions of the Scd galaxies IC 342 and NGC 6946, out to about 10 kpc, exhibits a falloff which follows the exponential luminosity profile from the stellar disk. The fact that neither galaxy shows a breach in the molecular gas like that found in the Milky Way between the nucleus and the molecular cloud annulus suggests a link between the deficiency of gas and the presence of either a nuclear bulge or an inner Lindblad resonance (ILR). Support for the association of the gap with the ILR or bulge is found in brief observations of NGC 4321, whose CO distribution appears to be like that of the Milky Way. In both Scd galaxies, the total mass of H2 inside about 10 kpc exceeds that in H I by a factor of approximately three. A global spiral structure is not evident in the molecular data.
No takes yet. Share an insight, caveat, or question.
Young et al. (1982) studied this question.