Publ. Astron. Soc. Japan, 36, 27-40 (1984)

Collisionless Boltzmann Simulation of Stellar Disks.
III. Deformation of Normal Modes to Bar Patterns

Mitsugu T. NISHIDA, Yosho WATANABE, Takao FUJIWARA, and Shoji KATO
Department of Astronomy, University of Kyoto, Sakyo-ku, Kyoto 606
(Received 1983 June 9; accepted 1983 November 14)


It is examined how spiral normal-mode perturbations superposed on equilibrium stellar disks evolve into the nonlinear regime. This investigation is made by numerical integration of the collisionless Boltzmann and Poisson equations. The unperturbed disks adopted are Toomre's (1963, Astrophys. J., 138, 385) model 1 with Kalnajs' (1976; AAA 17.151.040) velocity distribution function. The model parameter n is taken so that the disks are near the marginal stability to axisymmetric local perturbations. The results show that the normal spiral mode of two arms grows exponentially at the initial stage of small amplitude. At a certain stage, however, the growth is saturated, and the spiral pattern is deformed into a conspicuous bar. Processes involved in this deformation are discussed briefly in relation to angular momentum exchange between the pattern and stars.

Key words: Barred spiral galaxies; Collisionless Bltzmann simulation; Disk galaxies; Nonaxisymmetric global instability; Stellar Dynamics.