Systematic Perturbations of the Thermodynamic Properties in Cool Cores
  of HIFLUGCS Galaxy Clusters
  We present an ensemble X-ray analysis of systematic perturbations in the
central hot gas properties for a sample of 28 nearby strong cool-core systems
selected from the HIghest X-ray FLUx Galaxy Cluster Sample (HIFLUGCS). We
analyze their cool-core features observed with the Chandra X-ray Observatory.
All individual systems in our sample exhibit at least a pair of positive and
negative excess perturbations in the X-ray residual image after subtracting the
global brightness profile. We extract and analyze X-ray spectra of the
intracluster medium (ICM) in the detected perturbed regions. To investigate
possible origins of the gas perturbations, we characterize thermodynamic
properties of the ICM in the perturbed regions and characterize their
correlations between positive and negative excess regions. The best-fit
relations for temperature and entropy show a clear offset from the one-to-one
relation, $T_\mathrm{neg}/T_\mathrm{pos}=1.20^{+0.04}_{-0.03}$ and
$K_\mathrm{neg}/K_\mathrm{pos}=1.43\pm 0.07$, whereas the best-fit relation for
pressure is found to be remarkably consistent with the one-to-one relation
$P_\mathrm{neg}=P_\mathrm{pos}$, indicating that the ICM in the perturbed
regions is in pressure equilibrium. These observed features in the HIFLUGCS
sample are in agreement with the hypothesis that the gas perturbations in cool
cores are generated by gas sloshing. We also analyze synthetic observations of
perturbed cluster cores created from binary merger simulations, finding that
the observed temperature ratio agrees with the simulations,
$T_\mathrm{neg}/T_\mathrm{pos}\sim 1.3$. We conclude that gas sloshing induced
by infalling substructures plays a major role in producing the characteristic
gas perturbations in cool cores. The ubiquitous presence of gas perturbations
in cool cores may suggest a significant contribution of gas sloshing to
suppressing runaway cooling of the ICM.
