The Norris survey of the Corona Borealis supercluster. III. Structure and mass of the supercluster

We present a study of the structure and dynamics of the Corona Borealis supercluster (z approximate to 0.07) based on the redshifts of 528 galaxies in the supercluster. The galaxy distribution within Corona Borealis is clumpy and appears overall to be far from relaxed. Approximately one-third of the supercluster galaxies lie outside of the Abell clusters in the supercluster. A background supercluster at z approximate to 0.11 makes a substantial contribution to the projected surface density of galaxies in the Corona Borealis held. In order to estimate the mass of the supercluster, we have assumed that the mass of the supercluster is proportional to upsilon(2)r, where upsilon 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 similar to 25% for objects with overdensities greater than or similar to 5. Nonuniform spatial sampling can, however, cause systematic underestimates of as much as 30%. The projected mass estimator is less accurate but still provides useful estimates in most cases. 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) h(-1) M-circle dot, which yields a B-AB-band mass-to-light ratio of 564 h (M/L)(circle dot), on scales of -20 h(-1) Mpc. The background supercluster has a similar mass-to-light ratio of 726 h (M/L)(circle dot). 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) greater than or similar to 0.4 on supercluster scales.