We present a weak-lensing analysis of the z \simeq 1.4 galaxy cluster XMMU J2235.3-2557 , based on deep Advanced Camera for Surveys images .
Despite the observational challenge set by the high redshift of the lens , we detect a substantial lensing signal at the \gtrsim 8 \sigma level .
This clear detection is enabled in part by the high mass of the cluster , which is verified by our both parametric and non-parametric estimation of the cluster mass .
Assuming that the cluster follows a Navarro-Frenk-White mass profile , we estimate that the projected mass of the cluster within r = 1 Mpc is ( 8.5 \pm 1.7 ) \times 10 ^ { 14 } M _ { \sun } , where the error bar includes the statistical uncertainty of the shear profile , the effect of possible interloping background structures , the scatter in concentration parameter , and the error in our estimation of the mean redshift of the background galaxies .
The high X-ray temperature 8.6 _ { -1.2 } ^ { +1.3 } keV of the cluster recently measured with Chandra is consistent with this high lensing mass .
When we adopt the 1- \sigma lower limit as a mass threshold and use the cosmological parameters favored by the Wilkinson Microwave Anisotropy Probe 5-year ( WMAP5 ) result , the expected number of similarly massive clusters at z \gtrsim 1.4 in the 11 square degree survey is N \sim 5 \times 10 ^ { -3 } .
Therefore , the discovery of the cluster within the survey volume is a rare event with a probability \lesssim 1 % , and may open new scenarios in our current understanding of cluster formation within the standard cosmological model .