Pattern Speeds and Galaxy Morphology
  The morphology of a disk galaxy is closely linked to its kinematic state. This is because density wave features are likely made of spontaneously-formed modes which are allowed to arise in the galactic resonant cavity of a particular basic disk state. The pattern speed of a density wave is an important parameter that characterizes the wave and its associated resonances. Numerical simulations by various authors have enabled us to interpret some galaxies in terms of high or low pattern speeds. The potential-density phase-shift method for locating corotation radii is an effective new tool for utilizing galaxy morphology to determine the kinematic properties of galaxies. The dynamical mechanism underlying this association is also responsible for the secular evolution of galaxies. We describe recent results from the application of this new method to more than 150 galaxies in the Ohio State University Bright Galaxy Survey and other datasets. 
R. Buta (University of Alabama) and X. Zhang (George Mason University)