The Density Contrast of the Shapley Supercluster

TL;DR

This paper estimates the mass and density contrast of the Shapley Supercluster using X-ray cluster data and the Press-Schechter formalism, revealing its gravitational unbound state and minor influence on local group velocities.

Contribution

It provides the first detailed mass and density contrast calculation of the SSC based on X-ray cluster abundance and extended Press-Schechter analysis.

Findings

Mass of SSC: (4.4+-0.44)×10^{16} solar masses

Density contrast (1+delta): 1.76+-0.17

SSC contributes about 9% to local group velocity

Abstract

We calculate the density contrast of the Shapley Supercluster (SSC) based on the enhanced abundance of X-ray clusters in it using the extended Press-Schechter formalism. We derive a total SSC mass of M_tot=(4.4+-0.44)x10^{16} M_sun within a sphere of 50 Mpc centered at a distance of about 160 Mpc. The nonlinear fractional density contrast of the sphere is (1+delta)=1.76+-0.17 relative to the mean matter density in the Universe, but the contrast increases in the interior of the SSC. Including the cosmological constant, the SSC region is found to be gravitationally unbound. The SSC contributes only a minor portion (9.0%+-2.1%) of the peculiar velocity of the local group.