LoCuSS: the connection between brightest cluster galaxy activity, gas
  cooling and dynamical disturbance of X-ray cluster cores
  We study the distribution of projected offsets between the cluster X-ray
centroid and the brightest cluster galaxy (BCG) for 65 X-ray selected clusters
from the Local Cluster Substructure Survey (LoCuSS), with a median redshift of
z=0.23. We find a clear correlation between X-ray/BCG projected offset and the
logarithmic slope of the cluster gas density profile at 0.04r500 (alpha),
implying that more dynamically disturbed clusters have weaker cool cores.
Furthermore, there is a close correspondence between the activity of the BCG,
in terms of detected H_alpha and radio emission, and the X-ray/BCG offset, with
the line emitting galaxies all residing in clusters with X-ray/BCG offsets of
<~15 kpc. Of the BCGs with alpha < -0.85 and an offset < 0.02r500, 96 per cent
(23/24) have optical emission and 88 per cent (21/24) are radio active, while
none has optical emission outside these criteria. We also study the cluster gas
fraction (fgas) within r500 and find a significant correlation with X-ray/BCG
projected offset. The mean fgas of the `small offset' clusters (< 0.02r500) is
0.106+/-0.005 (sigma=0.03) compared to 0.145+/-0.009 (sigma=0.04) for those
with an offset > 0.02r500, indicating that the total mass may be systematically
underestimated in clusters with larger X-ray/BCG offsets. Our results imply a
link between cool core strength and cluster dynamical state consistent with the
view that cluster mergers can significantly perturb cool cores, and set new
constraints on models of the evolution of the intracluster medium.
