Anomalously Weak Dynamical Friction in Halos
arXiv:astro-ph/0508036 · doi:10.1007/978-1-4020-5573-7_31
Abstract
A bar rotating in a pressure-supported halo generally loses angular momentum and slows down due to dynamical friction. Valenzuela & Klypin report a counter-example of a bar that rotates in a dense halo with little friction for several Gyr, and argue that their result invalidates the claim by Debattista & Sellwood that fast bars in real galaxies require a low halo density. We show that it is possible for friction to cease for a while should the pattern speed of the bar fluctuate upward. The reduced friction is due to an anomalous gradient in the phase-space density of particles at the principal resonance created by the earlier evolution. The result obtained by Valenzuela & Klypin is probably an artifact of their adaptive mesh refinement method, but anyway could not persist in a real galaxy. The conclusion by Debattista & Sellwood still stands.
To appear in "Island Universes - Structure and Evolution of Disk Galaxies" ed. R. S. de Jong, 8 pages, 4 figures, .cls and .sty files included