Hubble Space Telescope Weak-lensing Study of the Galaxy Cluster XMMU
  J2235.3-2557 at z=1.4: A Surprisingly Massive Galaxy Cluster when the
  Universe is One-third of its Current Age
  We present a weak-lensing analysis of the z=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 >~ 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+-1.7) x 10^14 solar mass,
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
>~ 1.4 in the 11 square degree survey is N ~ 0.005. Therefore, the discovery of
the cluster within the survey volume is a rare event with a probability < 1%,
and may open new scenarios in our current understanding of cluster formation
within the standard cosmological model.
