The mass profile of the Coma galaxy cluster

We use a new redshift survey complete to m(R) similar or equal to 15.4 within 4.degrees 25 from the center of the Coma cluster to measure the mass profile 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 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(less than or equal to 10 h(-1) Mpc)= (1.65 +/- 0.41) x 10(15) h(-1) M-. (1 sigma error). Previous mass estimates derived from optical and X-ray observations are limited to r less than or equal to 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.