The Norris Survey of the Corona Borealis Supercluster. III. Structure and Mass of the Supercluster

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Abstract

(Abridged) We present a study of the structure and dynamics of the Corona Borealis Supercluster (z ~ 0.07) based on the redshifts for 528 galaxies in the supercluster. The galaxy distribution within Corona Borealis is clumpy and appears overall to be far from relaxed. A background supercluster at z ~ 0.11 makes a substantial contribution to the projected surface density of galaxies in the Corona Borealis field. In order to estimate the mass of the supercluster, we have assumed that the mass of the supercluster is proportional to v^2r, where v and r are suitable scale velocity and radius, respectively, and we have used N-body simulations of both critical- and low-density universes to determine the applicability of standard mass estimators based on this assumption. Although superclusters are obviously not in equilibrium, our simulations demonstrate that the virial mass estimator yields mass estimates with an insignificant bias and a dispersion of only ~25% for objects with overdensities >~ 5. Non-uniform spatial sampling can, however, cause systematic underestimates by as much as 30%. All of our simulated superclusters turn out to be bound, and based on the overdensity of the Corona Borealis supercluster, we believe it is also very likely to be bound and may well have started to collapse. The mass of Corona Borealis is at least 3 x 10^16 solar masses, which yields a B(AB)-band mass-to-light ratio of 564h (M/L)_solar on scales of ~20 h^-1 Mpc. The background supercluster has a mass-to-light ratio of 726h (M/L)_solar. By comparing the supercluster mass-to-light ratios with the critical mass-to-light ratio required to close the universe, we determine that Omega_0 >~ 0.4 on supercluster scales.

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