Dark matter core formation from outflow episodes

While cold dark matter numerical simulations predict steep, 'cuspy' density profiles for dark matter halos, observations favor shallower 'cores'. The introduction of baryons alleviates this discrepancy, notably as feedback-driven outflow episodes can expand the dark matter distribution. We present a simple model for the response of a dissipationless spherical system to a sudden gas outflow or inflow from its center. The response is divided into an instantaneous change of potential at constant velocities followed by an energy-conserving relaxation. The model is tested against NIHAO cosmological zoom-in simulations, where it successfully predicts the evolution of the inner dark matter profile between successive snapshots in a large number of cases, failing mainly during mergers. It thus provides a simple understanding of the formation of dark matter halo cores by supernova-driven outflows, which can be extended to other situations such as the formation of ultra-diffuse galaxies.