Stability of bending gravity perturbations in rotating galactic disks of finite thickness: Fluid dynamic description

Abstract A method is provided for the solution of the self-consistent system of the Euler fluid dynamics and Poisson equations describing collective oscillations of a self-gravitating, rotation-flattened galactic disk of finite but small thickness, using a linear perturbation framework. The dispersion properties of bending gravity perturbations, which compress/disperse the system’s medium in the direction normal to the midplane and propagate horizontally, are studied. It is shown that these antisymmetric to the plane perturbations in a disk, behaving like a compressible flow, are always stable macroscopically. The hypothesis is advanced that the small-sized vertical corrugation, often observed in flat galaxies even in the absence of close neighbors, results from the kinetic wave-star resonances by inverse Landau damping. A Boltzmann kinetic theory and particle-based computer modeling will be required to examine these resonances in detail, considering the behavior of galactic models over time at the microscopic level.