Kinematics of the Hercules Supercluster

The Hercules Supercluster consists of the Abell clusters 2147, 2151, and2152. Previous studies of the kinematics have been confounded by the difficultyof correctly assigning galaxies to the individual clusters, which are notwell-separated. Our study has a total of 468 available velocities for galaxiesin the region, 175 of them new. 414 galaxies are in the supercluster, aboutthree times the number used in the previous supercluster study. We verify theexistence of the three individual clusters and compute their individualdynamical parameters. We investigate several techniques for assigning galaxymembership to clusters in this crowded field. We use the KMM mixture-modelingalgorithm to separate the galaxies into clusters; we find that A2152 has ahigher mean velocity than previous studies have reported. A2147 and A2152 alsohave lower velocity dispersions: 821(+68)(-55) and 715(+81)(-61) km/s. Theassignment of galaxies to either A2152 or A2147 requires velocity and positioninformation. We study the kinematics of the supercluster using the two-bodyformalism of Beers, Geller, and Huchra (1982) and conclude that A2147 and A2151are probably bound to each other, and that the supercluster as a whole may alsobe bound. The mass of the supercluster, if bound, is $(7.6\pm2.0)\times 10^{15}h^{-1} M_{\sun}$; with the supercluster luminosity, $(1.4\pm0.2) \times 10^{13}h^{-2} L_{\sun}$, this yields Omega = 0.34\pm0.1$.Comment: 61 pages, 14 figures, accepted to A