Induced Nested Galactic Bars inside Assembling Dark Matter Halos

Abstract

We investigate the formation and evolution of nested bar systems in disk galaxies in a cosmological setting by following the development of an isolated dark matter (DM) and baryon density perturbation. The disks form within the assembling triaxial DM halos, and the feedback from the stellar evolution is accounted for in terms of supernovae and OB stellar winds. Focusing on a representative model, we show the formation of an oval disk and of a first generation of nested bars with characteristic subkiloparsec sizes and a few kiloparsec sizes. The system evolves through successive dynamical couplings and decouplings, forcing the gas inward, and settles in a state of resonant coupling. The inflow rate can support a broad range of activity within the central kiloparsec, from quasar to Seyfert types, supplemented by vigorous star formation as a by-product. The initial bar formation is triggered in response to the tidal torques from the triaxial DM halo, which acts as a finite perturbation. This first generation of bars does not survive for more than 4-5 Gyr; by that time, the secondary bar has totally dissolved, while the primary one has very substantially weakened, reduced to a fat oval. This evolution is largely due to chaos introduced by the interaction of the multiple nonaxisymmetric components.