Analytical dynamical models for double power-law galactic nuclei

Abstract

Motivated by the finding that the observed surface brightness profiles of many galactic nuclei are fitted well by double power laws, we explore a range of spherical self-consistent dynamical models with this light profile. We find that the corresponding deprojected volume density profile, phase- space density and line-of-sight velocity distribution of these models are fitted well by simple analytic approximations. We illustrate the application of these models by fitting a sample of approximately 25 galactic nuclei observed by the Hubble Space Telescope (HST). Without a central black hole and strong anisotropy the models generally predict a negligibly small kurtosis parameter k_4. These models with a simple distribution function are suited to seed N-body simulations of galactic nuclei with realistic density profiles for studying the evolution of these systems.