On the origin of dark matter cores in dwarf galaxies

In this paper, we study the dynamical stability and time-evolution of the central dark matter cores of low-mass (about 10(8)-10(9) M-circle dot) galactic haloes found in recent cold dark matter simulations at high redshift. From these simulations we extract three haloes, assembled by hierarchical merging, that at redshift z greater than or similar to 10 display a core, and we evolve them without further merging to low redshift using direct N-body integration. The central core in the dark matter profile is found to be dynamically stable: it survives for many crossing times without evolution into a cusp. This result supports the claim that the mass dependence of the central dark matter profiles of simulated haloes is a direct consequence of the power spectrum of primordial density fluctuations. In addition, we show that the simulated dark matter profiles, if they evolved in isolation, are consistent with the observed velocity dispersion profile of stars in the inner parts of the Draco dwarf spheroidal galaxy. Simple scaling arguments are reviewed which explain the evolution of the concentration parameter with redshift. We also review some arguments used to derive the logarithmic slope of the inner and outer density profile.