Extensive spiral structure and corotation resonance

Spiral density wave theories demand that grand-design spiral structure be b ounded, at most, between the inner and outer Lindblad resonances of the spi ral pattern. The corotation resonance lies between the outer and the inner Lindblad resonances. The locations of the resonances are at radii whose rat ios to each other are rather independent of the shape of the rotation curve . The measured ratio of outer to inner extent of spiral structure for a giv en spiral galaxy can be compared to the standard ratio of corotation to inn er Lindblad resonance radius. In the case that the measured ratio far excee ds the standard ratio, it is likely that the corotation resonance is within the bright optical disk. Studying such galaxies can teach us how the actio n of resonances sculpts the appearance of spiral disks. This paper reports observations of 140 disk galaxies, leading to resonance ratio tests for 109 qualified spiral galaxies. It lists candidates that have a good chance of having the corotation resonance radius within the bright optical disk.