Dark matter in disc galaxies – II. Density profiles as constraints on feedback scenarios

Abstract

The disparity between the density profiles of galactic dark matter haloes predicted by dark matter only cosmological simulations and those inferred from rotation curve decomposition, the so-called cusp–core problem, suggests that baryonic physics has an impact on dark matter density in the central regions of galaxies. Using a Markov Chain Monte Carlo analysis of galactic rotation curves we constrain density profiles and an estimated minimum radius for baryon influence, r1, which we couple with a feedback model to give an estimate of the fraction of matter within that radius that must be expelled to produce the observed halo profile. We examine the rotation curves of eight galaxies taken from the THINGS (The HI Nearby Galaxy Survey) data set and determine constraints on the radial density profiles of their dark matter haloes. For some of the galaxies, both cored haloes and cosmological ρ ∝ r−1 cusps are excluded which requires finely tuned baryonic feedback. For galaxies which exhibit extended cores in their haloes (e.g. NGC 925), the use of a split power-law halo profile yields models without the unphysical, sharp features seen in models based on the Einasto profile. We have found there is no universal halo profile which can describe all the galaxies studied here.