Discussion

Our new observations of galaxies towards the Shapely supercluster have, by surveying a large area away from known clusters, revealed substantial new large structures in the region. The cluster is part of a much large structure than was apparent from the previous observations, extending uniformly in two sheets over the whole region we surveyed to the South of the core of the SSC. We detected an additional 230 members of the SSC in our whole survey area, representing a 50% increase on the previous total of 492 SSC galaxies. Our measurements to the North of the cluster were much less complete (only one field in poor weather) so we cannot exclude the possibility that these sheets of galaxies extend equally to the North. Recent results by Bardelli, Zucca & Zamorani (1999) support this possibility: they have measured galaxies in 18 small (40 arcmin) inter-cluster fields North of the core of the SSC and also find an overdensity at the SSC velocity.

In Paper I the effect of the SSC on the dynamics of the Local Group was estimated. It was found that the mass in the cluster could account for at least 25% of the motion of the Local Group with respect to the cosmic microwave background. Our new data suggest that the SSC is at least 50% more massive with a significant part of the extra mass in the closer sub-region. The SSC therefore has a more important effect on the Local Group that previously thought, although we defer a detailed calculation until we have additional data (Proust et al. 1999, in preparation).

© Copyright Astronomical Society of Australia 1997