A New Weak-Lensing Analysis of MS 1224.7+2007

Abstract

Galaxy cluster mass distributions are useful probes of Ω0 and the nature of the dark matter. Large clusters will distort the observed shapes of background galaxies through gravitational lensing, allowing the measurement of the cluster mass distributions. For most cases, the agreement between weak-lensing and radial velocity mass measurements of clusters is reasonably good. There is, however, one significant exception, the z = 0.32 cluster MS 1224.7+2007, which has a lensing mass substantially greater than the virial mass and, also, a very high mass-to-light ratio. Since this controversial object might be an unusually dark mass, a follow-up study is definitely warranted. In this paper we study the mass and light distributions of MS 1224.7+2007 out to a projected radius of 800 h-1 kpc by measuring the gravitationally induced distortions of background galaxies. We detect a shear signal in the background galaxies in the radial range 275 ≤ r ≤ 275'' at the 5.5 σ level. The resultant mass map exhibits a peak centered on the dominant cluster galaxy and strong evidence for substructure, which is seen even more strongly in the galaxy distribution. Assuming that all the detected shear is due to mass at z = 0.32, we find a cluster mass-to-light ratio of M/LR = 640 ± 150 (M/LR)⊙. The mass profile is quite flat compared with other clusters, disagreeing with a pseudo–singular isothermal sphere at the 95% confidence level. Our mass and M/L estimates are consistent with the previous weak-lensing result. The discrepancy between the lensing and virial mass remains, although it might be partially explained by subclustering and infall perpendicular to the line of sight. This cluster remains a candidate dark object deficient in baryons and, as such, severely tests cosmological models.