An Equilibrium Dark Matter Halo with the Burkert Profile

Abstract

In this paper a prescription for generating an equilibrium spherical system depicted with cuspy density profiles is extended to a core density profile, the Burkert profile, which is observationally more suitable to dwarfs. By using a time-saving Monte Carlo method instead of N-body simulations, we show that the Burkert halo initialized with the distribution function that depends only on energy is in a practically stable equilibrium. The one generated using the local Maxwellian approximation is unstable, where the flat core density structure tends to steepen. This is fundamentally different from the previous study on a halo with cuspy density profile. The deviation of the unstable "Burkert" from the initial Burkert profile is found to be closely related to taking a Gaussian as the velocity distribution at any given point. The significance of not using the local Maxwellian approximation is further demonstrated by exploring the dynamical evolution of compact super star clusters in the Burkert halo. In particular, the local Maxwellian approximation will result in underestimating the dynamical friction and overestimating sinking time scale. Accordingly, it will lead to lower probability of forming massive bulges and young nuclear star clusters in bulgeless galaxies.