On the Effect of Interstellar Material on Stellar Non-Circular Velocities in Disk Galaxies

This paper re-examines the question of the secular increase of stellar non-circular velocities in the disk portions of the Galaxy and similar systems. The possible gravitational disturbances from interstellar gas inhomogeneities on spiral structure scales are discussed with the inclusion of forces from accompanying standing waves of star density. Attention is restricted to the disk portion of a galaxy, where a "local" and "thin disk" model is used. Based on this model, the process is shown to derive the required energy from the differential rotation and gravitation of the star disk. It is estimated numerically to produce important increases in the mean stellar velocity dispersions during galactic lifetimes under reasonable assumptions regarding the amount and distribution of the interstellar material.