2006ApJ...642..720J

We present a Hubble Space Telescope Advanced Camera for Surveys (ACS) weak-lensing study of RX J0849+4452 and RX J0848+4453, the two most distant (at z=1.26 and 1.27, respectively) clusters yet measured with weak lensing. The two clusters are separated by ∼4' from each other and appear to form a supercluster in the Lynx field. Using our deep ACS i₇₇₅ and z₈₅₀imaging, we detected weak-lensing signals around both clusters at ∼4 σ levels. The mass distribution indicated by the reconstruction map is in good spatial agreement with the cluster galaxies. From the singular isothermal sphere (SIS) fitting, we determined that RX J0849+4452 and RX J0848+4453 have similar projected masses of (2.0±0.6)x10¹⁴ and (2.1±0.7)x10¹⁴ M_☉, respectively, within a 0.5 Mpc (∼60") aperture radius. In order to compare the weak-lensing measurements with the X-ray results calibrated by the most recent low-energy quantum efficiency determination and time-dependent gain correction, we also reanalyzed the archival Chandra data and obtained T_X=3.8^+1.3_–0.7 and 1.7^+0.7_–0.4keV for RX J0849+4452 and RX J0848+4453, respectively. Combined with the X-ray surface brightness profile measurement under the assumption of an isothermal β-model, the temperature of RX J0849+4452 predicts that the projected mass of the cluster within r=0.5 Mpc is 2.3^+0.8_–0.4x10¹⁴ M_☉, consistent with the weak-lensing analysis. On the other hand, for RX J0848+4453 we find that the mass derived from this X-ray analysis is much smaller (6.3^+2.6_–1.5x10¹³ M_☉) than the weak-lensing measurement.