Mass Distribution and Bar Formation in Growing Disk Galaxy Models
  We report idealized simulations that mimic the growth of galaxy disks
embedded in responsive halos and bulges. The disks manifested an almost
overwhelming tendency to form strong bars that we found very difficult to
prevent. We found that fresh bars formed in growing disks after we had
destroyed the original, indicating that bar formation also afflicts continued
galaxy evolution, and not just the early stages of disk formation. This
behavior raises still more insistently the previously unsolved question of how
some galaxies avoid bars. Since our simulations included only collisionless
star and halo particles, our findings may apply to gas-poor galaxies only;
however the conundrum persists for the substantial unbarred fraction of those
galaxies. Our original objective was to study how internal dynamics rearranged
the distribution of mass in the disk as a generalization of our earlier study
with rigid spherical components. With difficulty, we were able to construct
some models that were not strongly influenced by bars, and found that halo
compression, and angular momentum exchange with the disk did not alter our
earlier conclusion that spiral activity is largely responsible for creating
smooth density profiles and rotation curves.
