How does our choice of observable influence our estimation of the centre
  of a galaxy cluster? Insights from cosmological simulations
  Galaxy clusters are an established and powerful test-bed for theories of both
galaxy evolution and cosmology. Accurate interpretation of cluster observations
often requires robust identification of the location of the centre. Using a
statistical sample of clusters drawn from a suite of cosmological simulations
in which we have explored a range of galaxy formation models, we investigate
how the location of this centre is affected by the choice of observable -
stars, hot gas, or the full mass distribution as can be probed by the
gravitational potential. We explore several measures of cluster centre: the
minimum of the gravitational potential, which would expect to define the centre
if the cluster is in dynamical equilibrium; the peak of the density; the centre
of BCG; and the peak and centroid of X-ray luminosity. We find that the centre
of BCG correlates more strongly with the minimum of the gravitational potential
than the X-ray defined centres, while AGN feedback acts to significantly
enhance the offset between the peak X-ray luminosity and minimum gravitational
potential. These results highlight the importance of centre identification when
interpreting clusters observations, in particular when comparing theoretical
predictions and observational data.
