The Dark Halo of NGC 5963 as a Constraint on Dark Matter Self‐Interaction at the Low‐Velocity Regime

Abstract

Self-interacting dark matter has been proposed as a hypothesis to explain the shallow central slopes of the density profiles of dark matter halos in galaxies. In order to be consistent with observational studies at scales of galaxy clusters, the cross section should scale inversely with the velocity of collision. In this paper we consider the mass density profile of the halo of the low surface brightness (LSB) galaxy NGC 5963 to place an upper limit on the dark matter cross section for collisions with velocities ~150 km s-1, i.e., at the low-velocity regime. After calibrating against cosmological simulations, we found that the large inferred dark matter concentration and central dark matter density in NGC 5963 are inconsistent with an effective collisional cross section per unit of mass >0.2 cm2 g-1. Corrections were applied in order to account for reduction of the core by the adiabatic contraction caused by cooling baryons. Our limits, which involve a number of simplifying, but always conservative, assumptions, exclude the last permitted interval for velocity-dependent cross sections to explain the flat density core in LSB galaxies. Implications for the nature of dark matter are also discussed.