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

Abstract

Using a redshift survey of 1779 galaxies and photometry from the Two Micron All Sky Survey covering 200 deg2, 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 mag fainter than M at the distance of Coma. We confirm the mass profile obtained by Geller, Diaferio, and 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/L = 75 ± 23 h M☉/L☉, 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 ± 32 h). The constant enclosed mass-to-light ratio with radius suggests that the 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 r200 may be as much as a factor of 2.5 larger than that outside r200. These data demonstrate that the K-band light is not positively biased with respect to the mass; we cannot rule out antibias. These results imply that Ωm = 0.17 ± 0.05. Estimates of possible variations in M/L with radius suggest that the density parameter is no smaller than Ωm ≈ 0.08.