Gas Density Perturbations in Cool Cores of CLASH Galaxy Clusters
  We present a systematic study of gas density perturbations in cool cores of
high-mass galaxy clusters. We select 12 relaxed clusters from the Cluster
Lensing And Supernova survey with Hubble (CLASH) sample and analyze their cool
core features observed with the Chandra X-ray Observatory. We focus on the
X-ray residual image characteristics after subtracting their global profile of
the X-ray surface brightness distribution. We find that all the galaxy clusters
in our sample have, at least, both one positive and one negative excess regions
in the X-ray residual image, indicating the presence of gas density
perturbations. We identify and characterize the locally perturbed regions using
our detection algorithm, and extract X-ray spectra of the intracluster medium
(ICM). The ICM temperature in the positive excess region is lower than that in
the negative excess region, whereas the ICM in both regions is in pressure
equilibrium in a systematic manner. These results indicate that gas sloshing in
cool cores takes place in more than 80% of relaxed clusters (95% CL). We
confirm this physical picture by analyzing synthetic X-ray observations of a
cool-core cluster from a hydrodynamic simulation, finding that our detection
algorithm can accurately extract both the positive and negative excess regions
and can reproduce the temperature difference between them. Our findings support
the picture that the gas density perturbations are induced by gas sloshing, and
a large fraction of cool-core clusters have undergone gas sloshing, indicating
that gas sloshing may be capable of suppressing runaway cooling of the ICM.
