STRONG DENSITY GRADIENTS ON DENSITY WAVES IN SPIRAL GALAXIES by KIN

The purpose of this study is to determine more accurately the marginal stability condition for axisymmetric waves since it is believed that an unstable axisymmetric wave could affect the amplification of spiral waves. An axisymmetric wave with a gradient term of velocity dispersion ( surface density ) is derived. Analysis of this axisymmetric wave with a gradient term for our own galaxy shows that the wave is essentially stable in a medium which is slightly unstable according to the local criterion. Thus, the axisymmetric wave will probably have no effect ( or at best only very slight effects ) on the amplification of spiral waves. Gereralization of the axisymmetric wave to the spiral wave is also discussed. It is conjectured that the spiral wave with a gradient term ( for those galaxies with a large bending structure ) could cause spiral wave emission and amplification. Thesis Supervisor: James W.-K. Mark Associate Professor of Applied Mathematics Title: