A statistically-selected Chandra sample of 20 galaxy clusters -- II. Gas
  properties and cool-core/non-cool core bimodality
  We investigate the thermodynamic and chemical structure of the intracluster
medium (ICM) across a statistical sample of 20 galaxy clusters analysed with
the Chandra X-ray satellite. In particular, we focus on the scaling properties
of the gas density, metallicity and entropy and the comparison between clusters
with and without cool cores (CCs). We find marked differences between the two
categories except for the gas metallicity, which declines strongly with radius
for all clusters (Z ~ r^{-0.31}), outside ~0.02 r500. The scaling of gas
entropy is non-self-similar and we find clear evidence of bimodality in the
distribution of logarithmic slopes of the entropy profiles. With only one
exception, the steeper sloped entropy profiles are found in CC clusters whereas
the flatter slope population are all non-CC clusters. We explore the role of
thermal conduction in stabilizing the ICM and conclude that this mechanism
alone is sufficient to balance cooling in non-CC clusters. However, CC clusters
appear to form a distinct population in which heating from feedback is required
in addition to conduction. Under the assumption that non-CC clusters are
thermally stabilized by conduction alone, we find the distribution of Spitzer
conduction suppression factors, f_c, to be log-normal, with a log (base 10)
mean of -1.50+/-0.03 (i.e. f_c=0.032) and log standard deviation 0.39+/-0.02.
