Anomalous anisotropic cross-correlations between WMAP CMB maps and SDSS
  galaxy distribution and implications on the dark flow scenario
  We search for the dark flow induced diffuse kinetic Sunyaev Zel'dovich (kSZ)
effect through CMB-galaxy cross correlation. Such angular correlation is
anisotropic, with a unique $cos(theta_DF)$ angular dependence and hence can be
distinguished from other components. Here, $theta_DF$ is the angle between the
opposite dark flow direction and the direction of the sky where the correlation
is measured. We analyze the KIAS-VAGC galaxy catalog of SDSS-DR7 and the WMAP
seven-year temperature maps, applying an unbiased optimal weighting scheme to
eliminate any statistically isotropic components and to enhance the dark flow
detection signal. Non-zero weighted cross correlations are detected at 3.5
sigma for the redshift bin z<0.1 and at 3 sigma for the bin 0.1<z<0.2, implying
the existence of statistically anisotropic components in CMB. However, further
analysis does not support the dark flow explanation. The observed directional
dependence deviates from the $\propto cos(theta_DF)$ relation expected, and
hence can not be explained by the presence of a single dark flow, and if the
observed cross correlation is generated by the dark flow induced kSZ effect,
the velocity would be too high (> 6000 km/s). We report this work as the first
attempt to search for dark flow through weighted CMB-galaxy cross correlation
and to draw the attention on the sources of the detected anomalous CMB-galaxy
cross correlation.
