Ring Formation in Viscous Differentially Rotating Galactic Disks

Ringlike structures (in H α, CO and radio continuum) in central galactic regions have been observed in a number of objects. They seem to be a basic feature of galactic structure (for references see Dickman et al., 1988). These observations can be summarized as follows: The typical mass of these rings is 108 – 109 M ⊙. The gas distribution is smoothly decreasing from the ring into the innermost galactic regions. The rings appear always at the turnover radius where the galactic rotation turns from rigid to differential rotation.