A New Weak Lensing Analysis of MS1224.7+2007

Abstract

Galaxy cluster mass distributions are useful probes of Omega_0 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 MS1224.7+2007, which has a lensing mass substantially larger 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 MS1224+2007 out to a projected radius of 800/h kpc by measuring the gravitationally-induced distortions of background galaxies. We detect a shear signal in the background galaxies in the radial range 27.5 arcsec < r < 275 arcsec at the 5.5 sigma level. The resultant mass map exhibits a peak centered on the dominant cluster galaxy and strong evidence for substructure which is even more strongly seen in the galaxy distribution. Assuming all the detected shear is due to mass at z=0.32 we find cluster mass-to-light ratio of M/L_R = 640 +/- 150. The mass profile is quite flat compared to 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-site. This cluster remains a candidate dark object deficient in baryons and as such severely tests cosmological models.