The evolution of galaxy cluster X-ray scaling relations
  We use numerical simulations to investigate, for the first time, the joint
effect of feedback from supernovae (SNe) and active galactic nuclei (AGN) on
the evolution of galaxy cluster X-ray scaling relations. Our simulations are
drawn from the Millennium Gas Project and are some of the largest
hydrodynamical N-body simulations ever carried out. Feedback is implemented
using a hybrid scheme, where the energy input into intracluster gas by SNe and
AGN is taken from a semi-analytic model of galaxy formation. This ensures that
the source of feedback is a population of galaxies that closely resembles that
found in the real universe. We show that our feedback model is capable of
reproducing observed local X-ray scaling laws, at least for non-cool core
clusters, but that almost identical results can be obtained with a simplistic
preheating model. However, we demonstrate that the two models predict opposing
evolutionary behaviour. We have examined whether the evolution predicted by our
feedback model is compatible with observations of high-redshift clusters.
Broadly speaking, we find that the data seems to favour the feedback model for
z<0.5, and the preheating model at higher redshift. However, a statistically
meaningful comparison with observations is impossible, because the large
samples of high-redshift clusters currently available are prone to strong
selection biases. As the observational picture becomes clearer in the near
future, it should be possible to place tight constraints on the evolution of
the scaling laws, providing us with an invaluable probe of the physical
processes operating in galaxy clusters.
