Bar‐driven Spiral Density Waves and Accretion in Gaseous Disks

Abstract

The nonlinear response to a periodic bar potential in a differentially rotating gaseous disk is studied. A comprehensive theory, based on the work of Shu, Yuan, & Lissauer and Yuan & Cheng, is developed further. This approach allows us to include the effects of viscosity and self-gravitation explicitly in the formulation, and calculates directly the streamlines of the gas flow distorted by the rotating bar potential. Using it, we show that a major morphological difference exists among the spiral waves excited at the three types of Lindblad resonance. Spirals associated with the outer Lindblad resonance are tightly wound, while those associated with the inner Lindblad resonances are relatively open. In general, spirals are trailing. However, those excited at the inner inner Lindblad resonance are leading. These results help us understand the underlying physics of the spiral structure revealed in the recent radio interferometric observations of the central regions of disk galaxies. The transport of angular momentum between the bar and the disk is related directly to these waves. The spiral waves excited at the inner Lindblad resonances would induce inflows of disk material toward the center, while those excited at the outer Lindblad resonance induce outflows. Formulae to estimate the rates of the inflows and outflows are derived, and they are used to examine the process of fueling of active galactic nuclei and starburst rings.