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K. Rines (CfA), M.J. Geller (SAO), M.J. Kurtz (CfA), A. Diaferio (Torino), T.H. Jarrett (IPAC/Caltech), J.P. Huchra (CfA)
Using a redshift survey of 1779 galaxies and photometry from the 2-Micron All-Sky Survey (2MASS) covering 200 square degrees, we calculate independent mass and light profiles for the infall region of the Coma cluster of galaxies. The redshift survey is complete to Ks=12.2 (622 galaxies), 1.2 magnitudes fainter than M*K_s at the distance of Coma. We confirm the mass profile obtained by Geller, Diaferio, & Kurtz. The enclosed mass-to-light ratio measured in the Ks band is approximately constant to a radius of 10 h-1 Mpc, where M/LK_s= 75±23 h (in solar units), in agreement with weak lensing results on similar scales. Within 2.5 h-1 Mpc, X-ray estimates yield similar mass-to-light ratios (67±32h). The constant enclosed mass-to-light ratio with radius suggests that K-band light from bright galaxies in clusters traces the total mass on scales \lesssim10 h-1 Mpc. Uncertainties in the mass profile imply that the mass-to-light ratio inside r200 may be as much as a factor of 2.5 larger than that outside r200. These data demonstrate that K-band light is not positively biased with respect to the mass; we cannot rule out antibias. These results imply \Omegam = 0.17 ±0.05. Estimates of possible variations in M/LK_s with radius suggest that the density parameter is no smaller than \Omegam \approx 0.08.
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The author(s) of this abstract have provided an email address for comments about the abstract: krines@cfa.harvard.edu