The effect of baryons on the inner density profiles of rich clusters
  We use the "Evolution and assembly of galaxies and their environments"
(EAGLE) cosmological simulation to investigate the effect of baryons on the
density profiles of rich galaxy clusters. We focus on EAGLE clusters with
$M_{200}>10^{14}~M_\odot$ of which we have six examples. The central brightest
cluster galaxies (BCGs) in the simulation have steep stellar density profiles,
$\rho_*(r) \propto r^{-3}$. Stars dominate the mass density for
$r<10~\rm{kpc}$, and, as a result, the total mass density profiles are steeper
than the Navarro-Frenk-White (NFW) profile, in remarkable agreement with
observations. The dark matter halo itself closely follows the NFW form at all
resolved radii ($r\gtrsim3.0~\rm{kpc}$). The EAGLE BCGs have similar surface
brightness and line-of-sight velocity dispersion profiles as the BCGs in the
sample of Newman et al., which have the most detailed measurements currently
available. After subtracting the contribution of the stars to the central
density, Newman et al. infer significantly shallower slopes than the NFW value,
in contradiction with the EAGLE results. We discuss possible reasons for this
discrepancy, and conclude that an inconsistency between the kinematical model
adopted by Newman et al. for their BCGs, which assumes isotropic stellar
orbits, and the kinematical structure of the EAGLE BCGs, in which the orbital
stellar anisotropy varies with radius and tends to be radially biased, could
explain at least part of the discrepancy.
