Weak-lensing detection at z-1.3:: measurement of the two lynx clusters with the advanced camera for surveys

We present a Hubble Space Telescope Advanced Camera for Surveys (ACS) weak-lensing study of RX J0849+4452 and RXJ0848+4453, the two most distant (at = 1.26 and 1.27, respectively) clusters yet measured with weak lensing. The two clusters are separated by similar to 4' from each other and appear to form a supercluster in the Lynx field. Using our deep ACS i(775) and z(850) imaging, we detected weak-lensing signals around both clusters at similar to 4 sigma 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 RXJ0848+4453 have similar projected masses of (2.0 +/- 0.6) x 10(14) and (2.1 +/- 0.7) x 10(14) M-circle dot, respectively, within a 0.5 Mpc (similar to 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(-0.73)(+1.3) and 1.7(-0.4)(+0.7) keV for RX J0849 and RX J0848+4453 respectively. Combined with the X-ray surface brightness profile measurement under the assumption of an isothermal beta-model, the temperature of RX J0849+4452 predicts that the projected mass of the cluster within r = 0.5 Mpc is is 2.3(-0.4)(+0.8) M-circle dot, consistent with the weaklensing analysis. On the other hand, for RX J0848+ 4453 we find that the mass derived fromthis X-ray analysis is much smaller (6.3(-1.5)(+2.6) 10(13) M-circle dot) than the weak-lensing measurement.