The time evolution of barred structures is examined under the influence of the external forces exerted by a spherical halo and by prolate halos. In particular, galaxy disks are placed in the plane including the major axis of prolate halos, whose configuration is often found in cosmological simulations. N-body disks in fixed external halo fields are simulated, so that bars are formed via dynamical instability. In the subsequent evolution, the bars in prolate halos dissolve gradually with time, while the bar pattern in a spherical halo remains almost unchanged to the end of the simulation. The decay times of the bars suggest that they can be destroyed in a time smaller than a Hubble time. Our results indicate that this dissolution process could occur in real barred galaxies, if they are surrounded by massive dark prolate halos, and the configuration adopted here is not unusual from the viewpoint of galaxy formation. For a prolate halo model, an additional simulation that is restricted to two-dimensional in-plane motions has also ended up with similar bar dissolution. This means that the vertical motions of disk stars do not play an essential role in the bar dissolution demonstrated here.

Subject headings: galaxies: evolution --- galaxies: halos --- galaxies: kinematics and dynamics --- galaxies: structure --- methods: n-body simulations