Disk Evolution and Bar Triggering Driven by Interactions with Dark Matter Substructure

Abstract

We study formation and evolution of bar-disk systems in fully self-consistent cosmological simulations of galaxy formation in the ΛCDM WMAP3 universe. In a representative model we find that the first generation of bars form in response to the asymmetric dark matter (DM) distribution (i.e., DM filament) and quickly decay. Subsequent bar generations form and are destroyed during the major merger epoch permeated by interactions with a DM substructure (subhalos). A long-lived bar is triggered by a tide from a subhalo and survives for ~10 Gyr. The evolution of this bar is followed during the subsequent numerous minor mergers and interactions with the substructure. Together with intrinsic factors, these interactions largely determine the stellar bar evolution. The bar strength and its pattern speed anticorrelate, except during interactions and the formation of a secondary (nuclear) bar. For about 5 Gyr bar pattern speed increases substantially despite the loss of angular momentum to stars and cuspy DM halo. We analyze the evolution of stellar populations in the bar-disk and relate them to the underlying dynamics. While the bar is made mainly of an intermediate age, ~5-6 Gyr, disk stars at z = 0, a secondary nuclear bar which surfaces at z ~ 0.1 is made of younger, ~1-3 Gyr stars.