Plan β: Core or cusp?

Abstract

The inner profile of dark matter (DM) haloes remains one of the central problems in small-scale cosmology. At present, the problem cannot be resolved in dwarf spheroidal galaxies due to a degeneracy between the DM profile and the velocity anisotropy β of the stellar population.We discuss a method which can break the degeneracy by exploiting 3D positions and 1D line-ofsight (LOS) velocities. With the full 3D spatial information, we can determine precisely what fraction of each stars LOS motion is in the radial and tangential direction. This enables us to infer the anisotropy parameter β directly from the data. The method is particularly effective if the galaxy is highly anisotropic. Finally, we argue that such a test could be applied to Sagittarius and potentially other dwarfs with RR Lyrae providing the necessary depth information. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.