Measuring the dark flow with public X-ray cluster data
  We present new results on the "dark flow" from a measurement of the dipole in
the distribution of peculiar velocities of galaxy clusters, applying the
methodology proposed and developed by us earlier. Our latest measurement is
conducted using new, low-noise 7-yr WMAP data as well as an all-sky sample of
X-ray selected galaxy clusters compiled exclusively from published catalogs.
Our analysis of the CMB signature of the kinematic Sunyaev-Zeldovich (SZ)
effect finds a statistically significant dipole at the location of galaxy
clusters. The residual dipole outside the cluster regions is small, rendering
our overall measurement 3-4 sigma significant. The amplitude of the dipole
correlates with cluster properties, being larger for the most X-ray luminous
clusters, as required if the signal is produced by the SZ effect. Since it is
measured at zero monopole, the dipole can not be due to the thermal SZ effect.
Our results are consistent with those obtained earlier by us from 5-yr WMAP
data and using a proprietary cluster catalog. In addition, they are robust to
quadrupole removal, demonstrating that quadrupole leakage contributes
negligibly to the signal. The lower noise of the 7-yr WMAP also allows us, for
the first time, to obtain tentative empirical confirmation of our earlier
conjecture that the adopted filtering flips the sign of the KSZ effect for
realistic clusters and thus of the deduced direction of the flow. The latter is
consistent with our earlier measurement in both the amplitude and direction.
Assuming the filtering indeed flips the sign of the KSZ effect from the
clusters, the direction agrees well also with the results of independent work
using galaxies as tracers at lower distances. We make all maps and cluster
templates derived by us from public data available to the scientific community
to allow independent tests of our method and findings.
