SELF-CONSISTENT SPIRAL GALACTIC MODELS

A family of models with adjustable parameters are applied to twelve normal spiral galaxies with known rotation curves and surface photometry. The galaxies form a representative sample of Sa, Sb and Sc galaxies with different total mass and mass concentration. For each model the response density is calculated by superposition of a large number of orbits, and a comparison is made with the imposed density. Three theoretical possibilities are examined. (a) Small perturbation linear theory with the end of the spiral at corotation, (b) Strong perturbation nonlinear theory with the end at corotation, and (c) Strong perturbation nonlinear theory with the end at the 4/1 resonance. In all Sb and Sc galaxies the best self-consistent model is the nonlinear model ending at the 4/1 resonance, while in the Sa galaxies the spiral arms are weak and the best theoretical model is a linear one ending at corotation.