Constraining the distribution of dark matter in dwarf spheroidal galaxies with stellar tidal streams

Abstract

Abstract We use high-resolution N-body simulations to follow the formation and evolution of tidal streams associated with dwarf spheroidal galaxies (dSphs). The dSph models are embedded in dark matter (DM) haloes with either a centrally divergent ‘cusp’, or a homogeneous-density ‘core’. In agreement with previous studies, we find that as tides strip the galaxy the evolution of the half-light radius and the averaged velocity dispersion follows well-defined tracks that are mainly controlled by the amount of mass lost. Crucially, the evolutionary tracks behave differently depending on the shape of the DM profile: at a fixed remnant mass, dSphs embedded in cored haloes have larger sizes and higher velocity dispersions than their cuspy counterparts. The divergent evolution is particularly pronounced in galaxies whose stellar component is strongly segregated within their DM halo and becomes more disparate as the remnant mass decreases. Our analysis indicates that the DM profile plays an important role in defining the internal dynamics of tidal streams. We find that stellar streams associated with cored DM models have velocity dispersions that lie systematically above their cuspy counterparts. These results suggest that modelling the dynamics of streams with known dSph progenitors may reveal the distribution of DM on the smallest galactic scales.