2014MNRAS.439.1897K

We utilize Young's algorithm to model the adiabatic compression of the dark matter haloes of galaxies in the THINGS survey to determine the relationship between the halo fit to the rotation curve and the corresponding primordial halo prior to compression. Young's algorithm conserves radial action and angular momentum, resulting in less halo compression than more widely utilized approximations. We find that estimates of the parameters of NFW haloes fit to the current dark matter distribution systematically overestimate the concentration and underestimate the virial velocity of the corresponding primordial halo. It is the latter that is predicted by dark matter simulations; so accounting for compression is a necessary step for evaluating whether massive galaxies are consistent with dark matter-only simulations. The inferred primordial haloes broadly follow the c-V200 relation expected in a Λcold dark matter (ΛCDM) cosmogony, but often scatter to lower concentrations. We are unable to obtain fits at all for those galaxies whose current dark matter haloes are poorly described by the NFW form. We thus find a mixed bag: some galaxies are reasonably well described by adiabatic compression within a primordial NFW halo, while others require an additional mechanism that reduces the density of dark matter below the primordial initial condition.