Structure and dynamics of the Shapley Supercluster

Abstract

We present the first results of our wide-field redshift survey of galaxies in a 285 square degree region of the Shapley Supercluster (SSC) based on a set of 8341 galaxy velocities obtained from various telescopes and literature. Our data reveal that the main plane of the SSC (v ~ 14500km/s) extends further than previously realised, filling the whole extent of our survey region of 12 degrees by 30 degrees on the sky (42 Mpc by 105 Mpc, Ho=75 km/s/Mpc). There is also a significant structure associated with the slightly nearer Abell 3571 cluster complex (v ~ 12000km/s) with a caustic structure evident out to a radius of 6 Mpc. These galaxies seem to link two previously identified sheets of galaxies and establish a connection with a third one at <v> = 15000km/s near R.A.= 13h. They also tend to fill the gap of galaxies between the foreground Hydra-Centaurus region and the more distant SSC. In the velocity range (9000 < cz < 18000km/s) of the Shapley supercluster, we calculate galaxy overdensities of 7.0 +/- 0.2 over the 225 square degree central region and 4.8 +/- 0.2 in a 192 square degree region excluding rich clusters. Over the large region of our survey the inter-cluster galaxies make up 48% of all galaxies in the SSC region and may contribute a similar amount of mass to the cluster galaxies. We discuss the completeness of the velocity catalogue, the results obtained of a spherical collapse model used to estimate the SSC mass profile and its contributions to the peculiar motion of the Local Group with respect to the cosmic microwave background.