Subaru weak-lensing measurement of a z = 0.81 cluster discovered by the
  Atacama Cosmology Telescope Survey
  We present a Subaru weak lensing measurement of ACT-CL J0022.2-0036, one of
the most luminous, high-redshift (z=0.81) Sunyaev-Zel'dovich (SZ) clusters
discovered in the 268 deg^2 equatorial region survey of the Atacama Cosmology
Telescope. For the weak lensing analysis using i'-band images, we use a
model-fitting (Gauss-Laguerre shapelet) method to measure shapes of galaxy
images, where we fit galaxy images in different exposures simultaneously to
obtain best-fit ellipticities taking into account the different PSFs in each
exposure. We also take into account the astrometric distortion effect on galaxy
images by performing the model fitting in the world coordinate system. To
select background galaxies behind the cluster at z=0.81, we use photometric
redshift (photo-z) estimates for every galaxy derived from the co-added images
of multi-passband Br'i'z'Y, with PSF matching/homogenization. After a photo-z
cut for background galaxy selection, we detect the tangential weak lensing
distortion signal with a total signal-to-noise ratio of about 3.7. By fitting a
Navarro-Frenk-White model to the measured shear profile, we find the cluster
mass to be M_200\bar{\rho}_m = [7.5^+3.2_-2.8(stat.)^+1.3_-0.6(sys.)] x 10^14
M_\odot/h. The weak lensing-derived mass is consistent with previous mass
estimates based on the SZ observation, with assumptions of hydrostatic
equilibrium and virial theorem, as well as with scaling relations between SZ
signal and mass derived from weak lensing, X-ray, and velocity dispersion,
within the measurement errors. We also show that the existence of ACT-CL
J0022.2-0036 at z=0.81 is consistent with the cluster abundance prediction of
the \Lambda-dominated cold dark matter structure formation model. We thus
demonstrate the capability of Subaru-type ground-based images for studying weak
lensing of high-redshift clusters.
