2005ApJ...634..813J

We present Hubble Space Telescope Advanced Camera for Surveys (ACS) weak-lensing and Chandra X-ray analyses of MS 1054-0321 at z=0.83, the most distant and X-ray-luminous cluster in the Einstein Extended Medium-Sensitivity Survey (EMSS). The high-resolution mass reconstruction through ACS weak lensing reveals the complicated dark matter substructure in unprecedented detail, characterized by the three dominant mass clumps with the four or more minor satellite groups within the current ACS field. The direct comparison of the mass map with the Chandra X-ray image shows that the eastern weak-lensing substructure is not present in the X-ray image and, more interestingly, the two X-ray peaks are displaced away from the hypothesized merging direction with respect to the corresponding central and western mass clumps, possibly because of ram pressure. In addition, as observed in our previous weak-lensing study of another high-redshift cluster CL 0152-1357 at z=0.84, the two dark matter clumps of MS 1054-0321 seem to be offset from the galaxy counterparts. We examine the significance of these offsets and discuss a possible scenario, wherein the dark matter clumps might be moving ahead of the cluster galaxies. The nonparametric weak-lensing mass modeling gives a projected mass of M(r<1 Mpc)=(1.02±0.15)x10¹⁵ M_☉, where the uncertainty reflects both the statistical error and the cosmic shear effects. Our temperature measurement of T=8.9^+1.0_–0.8keV utilizing the newest available low-energy quantum efficiency degradation prescription for the Chandra instrument, together with the isothermal β description of the cluster (r_c=16''±15'' and β=0.78±0.08), yields a projected mass of M(r<1 Mpc)=(1.2±0.2)x10¹⁵ M_☉, consistent with the weak-lensing result.