1999ApJ...517L..23G

We use a new redshift survey complete to m_R≃15.4 within 4°.25 from the center of the Coma cluster to measure the mass profile of the cluster to r∼5.5 h^–1 Mpc. We extend the profile to r∼10 h^–1 Mpc with a further sample complete to m_R=15.4 in 42% of the area within a 10° radius and to m_Zw=15.5 in the remaining area. Galaxies within this region are falling onto the cluster on moderately radial orbits and thus do not satisfy virial equilibrium. Nonetheless, identification of the caustics in redshift space provides an estimate of the gravitational potential at radius r and hence of the system mass, M(≤10 h^–1 Mpc)=(1.65±0.41)x10¹⁵ h^–1 M_☉ (1 σ error). Previous mass estimates derived from optical and X-ray observations are limited to r≤2.5 h^–1 Mpc. Our mass profile is consistent with these estimates but extends to distances 4 times as large. Over the entire range, the mass increases with r at the rate expected for a Navarro, Frenk, & White density profile.