Title:Unstable Spiral Modes in Galaxies: Modeling vs Observations

Abstract:
There is no consensus as to whether the spirals are a long-lived phenomenon or reappear many times during 
the galactic evolution. Some researchers advocate long-lived spirals manifesting the unstable global modes. 
Others favor short-lived or recurrent patterns developing through swing amplification in shearing flows. We 
test the applicability of the global modal approach in the density wave theory of spiral structure for a sample 
of spiral galaxies that have a variety of spiral patterns. By using the observed radial distributions of the stellar 
velocity dispersions and the rotation curves, we construct equilibrium models for the galactic disks in each 
galaxy. We model then the dynamics of the spiral perturbations using linear global modal analysis and 
nonlinear hydro- and N-body simulations. Both approaches reproduce qualitatively well the observed 
properties of the spiral arms in the galactic disks.