Constraining the inner density slope of massive galaxy clusters

We determine the inner density profiles of massive galaxy clusters M$_{200}$ > $5 \times 10^{14}$ M$_{\odot}$ in the Cluster-EAGLE (C-EAGLE) hydrodynamic simulations, and investigate whether the dark matter density profiles can be correctly estimated from a combination of mock stellar kinematical and gravitational lensing data. From fitting mock stellar kinematics and lensing data generated from the simulations, we find that the inner density slopes of both the total and the dark matter mass distributions can be inferred reasonably well. We compare the density slopes of C-EAGLE clusters with those derived by Newman et al. for 7 massive galaxy clusters in the local Universe. We find that the asymptotic best-fit inner slopes of "generalized" NFW (gNFW) profiles, ${\gamma}_{\rm gNFW}$, of the dark matter haloes of the C-EAGLE clusters are significantly steeper than those inferred by Newman et al. However, the mean mass-weighted dark matter density slopes, $\bar{\gamma}_{\rm dm}$, are remarkably similar in the simulated and real clusters. We also find that the estimate of ${\gamma}_{\rm gNFW}$ is very sensitive to the weak lensing measurements in the outer parts of the cluster and a bias in the estimate of the scale radius, $r_{\rm s}$, inferred from these measurements can lead to an underestimate of ${\gamma}_{\rm gNFW}$.