The mass profile of the Coma galaxy cluster

We use a new redshift survey complete to m(R) similar or equal to 15.4 with in 4.degrees 25 from the center of the Coma cluster to measure the mass pro file of the cluster to r similar to 5.5 h(-1) Mpc. We extend the profile to r similar to 10 h(-1) Mpc with a further sample complete to m(R) = 15.4 in 42% of the area within a 10 degrees radius and to m(zw) = 15.5 in the rema ining area. Galaxies within this region are falling onto the cluster on mod erately radial orbits and thus do not satisfy virial equilibrium. Nonethele ss, identification of the caustics in redshift space provides an estimate o f the gravitational potential at radius r and hence of the system mass, M(l ess than or equal to 10 h(-1) Mpc)= (1.65 +/- 0.41) x 10(15) h(-1) M-. (1 s igma error). Previous mass estimates derived from optical and X-ray observa tions are limited to r less than or equal to 2.5 h(-1) Mpc. Our mass profil e is consistent with these estimates but extends to distances 4 times as la rge. Over the entire range, the mass increases with r at the rate expected for a Navarro, Frenk, & White density profile.