K. Holley-Bockelmann (Pennsylvania State University), M. Weinberg (University of Massachusetts)
Both theory and simulations reveal that a cuspy dark matter halo drains angular momentum from the bar. Unfortunately, this slows the bar pattern too effectively to match the observations of rapidly rotating barred galaxies in the local universe. Using fully self-consistent N-body simulations, we demonstrate that bars do not appreciably slow when embedded in dark matter halos with flat central density profiles. This occurs even when the disk is significantly submaximal, so it appears that the fraction of dark to baryonic matter at the center of a galaxy does not determine the pattern speed of the bar. We argue that the bar slowdown rate is controlled instead by the phase space density gradient at the dark matter halo's center. If dark matter halo cusps are flattened by dynamical interactions with primordial bars, substructure, or 3-body scattering, we expect the bars formed in these evolved systems to be fast.
Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.