Testing for X-ray-SZ Differences and Redshift Evolution in the X-ray
  Morphology of Galaxy Clusters
  We present a quantitative study of the X-ray morphology of galaxy clusters,
as a function of their detection method and redshift. We analyze two separate
samples of galaxy clusters: a sample of 36 clusters at 0.35 < z < 0.9 selected
in the X-ray with the ROSAT PSPC 400 deg2 survey, and a sample of 90 clusters
at 0.25 < z < 1.2 selected via the Sunyaev-Zel'dovich (SZ) effect with the
South Pole Telescope. Clusters from both samples have similar-quality Chandra
observations, which allow us to quantify their X-ray morphologies via two
distinct methods: centroid shifts and photon asymmetry. The latter technique
provides nearly unbiased morphology estimates for clusters spanning a broad
range of redshift and data quality. We further compare the X-ray morphologies
of X-ray- and SZ-selected clusters with those of simulated clusters. We do not
find a statistically significant difference in the measured X-ray morphology of
X-ray and SZ-selected clusters over the redshift range probed by these samples,
suggesting that the two are probing similar populations of clusters. We find
that the X-ray morphologies of simulated clusters are statistically
indistinguishable from those of X-ray- or SZ-selected clusters, implying that
the most important physics for dictating the large-scale gas morphology
(outside of the core) is well-approximated in these simulations. Finally, we
find no statistically significant redshift evolution in the X-ray morphology
(both for observed and simulated clusters), over the range z ~ 0.3 to z ~ 1,
seemingly in contradiction with the redshift-dependent halo merger rate
predicted by simulations.
