The effect of AGN feedback on the X-ray morphologies of clusters --
  simulations vs. observations
  We study the effect of Active Nuclei Galaxy (AGN) feedback as one of the
major mechanisms modifying the cluster morphology influencing scaling
relations, which are the most uncertain factor in constraining cosmology with
clusters of galaxies. Using cosmological hydrodynamical simulations we
investigate how the AGN feedback changes the X-ray morphology of the simulated
systems, and compare to the observed REXCESS (Representative XMM-Newton Cluster
Structure Survey) clusters. We apply centre shifts and power ratios to
characterise the cluster morphology, and find that our simulated clusters are
more substructured than the observed ones. We show that the degree of this
discrepancy is affected by the inclusion of AGN feedback. While the clusters
simulated with the AGN feedback are in much better agreement with the REXCESS
L_X-T relation, they are also more substructured, which increases the tension
with observations. This suggests that not only global cluster properties such
as L_X and T and radial profiles should be used to compare and to calibrate
simulations with observations, but also substructure measures such as centre
shifts and power ratios. We discuss what changes in the simulations might ease
the tension with observational constraints on these quantities.
