High-Redshift Cool-Core Galaxy Clusters Detected via the
  Sunyaev--Zel'dovich Effect in the South Pole Telescope Survey
  We report the first investigation of cool-core properties of galaxy clusters
selected via their Sunyaev--Zel'dovich (SZ) effect. We use 13 galaxy clusters
uniformly selected from 178 deg^2 observed with the South Pole Telescope (SPT)
and followed up by the Chandra X-ray Observatory. They form an approximately
mass-limited sample (> 3 x 10^14 M_sun h^-1_70) spanning redshifts 0.3 < z <
1.1. Using previously published X-ray-selected cluster samples, we compare two
proxies of cool-core strength: surface brightness concentration (cSB) and
cuspiness ({\alpha}). We find that cSB is better constrained. We measure cSB
for the SPT sample and find several new z > 0.5 cool-core clusters, including
two strong cool cores. This rules out the hypothesis that there are no z > 0.5
clusters that qualify as strong cool cores at the 5.4{\sigma} level. The
fraction of strong cool-core clusters in the SPT sample in this redshift regime
is between 7% and 56% (95% confidence). Although the SPT selection function is
significantly different from the X-ray samples, the high-z cSB distribution for
the SPT sample is statistically consistent with that of X-ray-selected samples
at both low and high redshifts. The cool-core strength is inversely correlated
with the offset between the brightest cluster galaxy and the X-ray centroid,
providing evidence that the dynamical state affects the cool-core strength of
the cluster. Larger SZ-selected samples will be crucial in understanding the
evolution of cluster cool cores over cosmic time.
