Velocity Distributions from Nonextensive Thermodynamics

There is no accepted mechanism that explains the equilibrium structures thatform in collisionless cosmological N-body simulations. Recent work hasidentified nonextensive thermodynamics as an innovative approach to theproblem. The distribution function that results from adopting this frameworkhas the same form as for polytropes, but the polytropic index is now related tothe degree of nonextensiveness. In particular, the nonextensive approach canmimic the equilibrium structure of dark matter density profiles found insimulations. We extend the investigation of this approach to the velocitystructures expected from nonextensive thermodynamics. We find that thenonextensive and simulated N-body rms-velocity distributions do not match oneanother. The nonextensive rms-velocity profile is either monotonicallydecreasing or displays little radial variation, each of which disagrees withthe rms-velocity distributions seen in simulations. We conclude that thecurrently discussed nonextensive models require further modifications in orderto corroborate dark matter halo simulations. (adapted from TeX)Comment: 3 color figures, accepted for publication in Ap