The tidal velocity field in the Local Supercluster

In addition to the usual Virgocentric infall velocities, a significant quadrupolar tidal velocity field has been detected in the Local Supercluster, due to the density structure outside it. This tidal field is not caused by a single external structure, but the Hydra-Centaurus supercluster appears to be a major contributor, since the eigenvector associated with the largest positive eigenvalue of the quadrupole points in its direction. At the distance of the Virgo Cluster the eigenvalues of the tidal field are about 200 km/s, but the component in the direction of Virgo is only 46 + or - 70. The determination of the cosmological density parameter from the Virgocentric infall is therefore little affected by the addition of the tidal field. The residual random ('thermal') velocity of the Local Group relative to its nearest neighbors is 72 + or - 37 km/s, which is not statistically significant.