The velocity--shape alignment of clusters and the kinetic
  Sunyaev--Zeldovich effect
  We use the Millennium simulation to probe the correlation between cluster
velocities and their shapes and the consequences for measurements of the
kinetic Sunyaev-Zeldovich (kSZ) effect. Halos are generally prolate ellipsoids
with orientations that are correlated with those of nearby halos. We measure
the mean streaming velocities of halos along the lines that separate them,
demonstrating that the peculiar velocities and the long axes of halos tend to
be somewhat aligned, especially for the most massive halos. Since the kSZ
effect is proportional to the line-of-sight velocity and the optical depth of
the cluster, the alignment results in a strong enhancement of the kSZ signature
in clusters moving along the line of sight. This effect has not been taken into
account in many analyses of kSZ signatures.
