Hubble Space TelescopeAdvanced Camera for Surveys Weak‐Lensing andChandraX‐Ray Studies of the High‐Redshift Cluster MS 1054−0321

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 mostdistant and X-ray luminous cluster in the Einstein Extended Medium-SensitivitySurvey (EMSS). The high-resolution mass reconstruction through ACS weak-lensingreveals the complicated dark matter substructure in unprecedented detail,characterized by the three dominant mass clumps with the four or more minorsatellite groups within the current ACS field. The direct comparison of themass map with the Chandra X-ray image shows that the eastern weak-lensingsubstructure is not present in the X-ray image and, more interestingly, the twoX-ray peaks are displaced away from the hypothesized merging direction withrespect to the corresponding central and western mass clumps, possibly becauseof ram pressure. In addition, as observed in our previous weak-lensing study ofanother high-redshift cluster CL 0152-1357 at z=0.84, the two dark matterclumps of MS 1054-0321 seem to be offset from the galaxy counterparts. Weexamine the significance of these offsets and discuss a possible scenario,wherein the dark matter clumps might be moving ahead of the cluster galaxies.The non-parametric weak-lensing mass modeling gives a projected mass of M(r<1Mpc)=(1.02+-0.15)x 10^{15} solar mass, where the uncertainty reflects both thestatistical error and the cosmic shear effects. Our temperature measurement ofT=8.9_{-0.8}^{+1.0} keV utilizing the newest available low-energy quantumefficiency degradation prescription for the Chandra instrument, together withthe isothermal beta description of the cluster (r_c=16"+-15" andbeta=0.78+-0.08), yields a projected mass of M(r<1 Mpc)=(1.2+-0.2) x 10^{15}solar mass, consistent with the weak-lensing result.