Infrared Mass - to - Light Profile Throughout the Infall Region of the Coma Cluster

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 K s = 12.2 (622 galaxies), 1.2 magnitudes fainter than M * Ks at the distance of Coma. We confirm the mass profile obtained by Geller, Diaferio, & Kurtz. The enclosed mass-to-light ratio measured in the K s band is approximately constant to a radius of 10 h −1 Mpc, where M/L Ks = 75 ± 23hM ⊙ /L ⊙ , in agreement with weak lensing results on similar scales. Within 2.5h −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 10 h −1 Mpc. Uncertainties in the mass profile imply that the mass-to-light ratio inside r 200 may be as much as a factor of 2.5 larger than that outside r 200. These data demonstrate that K-band light is not positively biased with respect to the mass; we cannot rule out antibias. These results imply Ω m = 0.17 ± 0.05. Estimates of possible variations in M/L Ks with radius suggest that the density parameter is no smaller than Ω m ≈ 0.08.