How supernova feedback turns dark matter cusps into cores

TL;DR

This paper introduces a new analytical model explaining how energetic feedback from star formation and gas outflows in early galaxies can irreversibly transform dark matter cusps into cores, supported by cosmological simulations.

Contribution

It presents a novel impulsive approximation model that describes the physical process of cusp-core transformation due to rapid potential fluctuations.

Findings

The model successfully matches cosmological simulation results.

Dark matter cores can form with only a small fraction of baryons converting into stars.

Cores are maintained in dwarf galaxies over cosmic time.

Abstract

We propose and successfully test against new cosmological simulations a novel analytical description of the physical processes associated with the origin of cored dark matter density profiles. In the simulations, the potential in the central kiloparsec changes on sub-dynamical timescales over the redshift interval 4 > z > 2 as repeated, energetic feedback generates large underdense bubbles of expanding gas from centrally-concentrated bursts of star formation. The model demonstrates how fluctuations in the central potential irreversibly transfer energy into collisionless particles, thus generating a dark matter core. A supply of gas undergoing collapse and rapid expansion is therefore the essential ingredient. The framework, based on a novel impulsive approximation, breaks with the reliance on adiabatic approximations which are inappropriate in the rapidly-changing limit. It shows that both outflows and galactic fountains can give rise to cusp-flattening, even when only a few per cent of the baryons form stars. Dwarf galaxies maintain their core to the present time. The model suggests that constant density dark matter cores will be generated in systems of a wide mass range if central starbursts or AGN phases are sufficiently frequent and energetic.