On the origin of dark matter cores in dwarf galaxies

Abstract

ABSTRACT In this paper, we study the dynamical stability and time evolution of the central dark mattercores of low-mass (about10 8 − 10 9 M ⊙ ) galactic haloes found in recent cold dark mattersimulations at high redshift. From those simulations we extract three haloes, assembled byhierarchical merging, that at redshift z ∼ > 10 display a core and we evolve them without fur-ther merging to low redshift using direct N-body integration. The central core in the darkmatter profile is found to be dynamically stable: it survives for many crossing times withoutevolution into a cusp. This result supports the claim that the mass dependence of the centraldark matter profiles of simulated haloes is a direct conseque nce of the power spectrum ofprimordial density fluctuations. In addition, we show that t he simulated dark matter profiles,if they evolved in isolation, are consistent with the observed velocity dispersion profile ofstars in the inner parts of the Draco dwarf spheroidal galaxy. Simple scaling arguments arereviewed which explain the evolution of the concentration parameter with redshift. We alsoreview some arguments used to derive the logarithmic slope of the inner and outer densityprofile.Key words: cosmology: theory, dark matter – galaxies: dwarf, clusters, haloes – methods:N-body simulations