Extensive Spiral Structure and Corotation Resonance

Spiral density wave theories demand that grand design spiral structure bebounded, at most, between the inner and outer Lindblad resonances of the spiralpattern. The corotation resonance lies between the outer and inner Lindbladresonances. The locations of the resonances are at radii whose ratios to eachother are rather independent of the shape of the rotation curve. The measuredratio of outer to inner extent of spiral structure for a given spiral galaxycan be compared to the standard ratio of corotation to inner Lindblad resonanceradius. In the case that the measured ratio far exceeds the standard ratio, itis likely that the corotation resonance is within the bright optical disk.Studying such galaxies can teach us how the action of resonances sculpts theappearance of spiral disks. This paper reports observations of 140 diskgalaxies, leading to resonance ratio tests for 109 qualified spirals. It listscandidates that have a good chance of having the corotation resonance radiuswithin the bright optical disk.Comment: 29 pages, 7 figure files, AAS late