  We report the first result of weak gravitational lensing survey on a 2.1 sq
deg Rc-band image taken with a wide field camera (Suprime-Cam) on the prime
focus of 8.2 m Subaru Telescope. The weak lensing mass reconstruction is
applied to the data to search for dark matter halos of cluster scale; M >=
10^14 solar mass. The reconstructed convergence field is divided by 1-sigma
noise to obtain the signal-to-noise ratio map (S/N-map) of the detection. Local
maxima and minima are searched on the S/N-map and the probability distribution
function (PDF) of the peaks are created to compare with model predictions. We
found excess over noise PDF created from the randomized realization on both
positive and negative sides. Negative peaks imply the presence of voids in the
dark matter distribution and this is the first report of the detection.
Positive peaks, on the other hand, represent the dark matter halos and the
number count of the halos on the 2.1 sq deg image is 4.9 +- 2.3 for S/N > 5
where the Gaussian smoothing radius of the convergence map is 1'. The result is
consistent with the prediction assuming the Press-Schechter mass function and
the NFW halo profile under the cluster normalized CDM cosmology. Although the
present statistics is not enough due to the limited field of view, this work
demonstrates that dark matter halo count via weak lensing is a promising way to
test the paradigm of structure formation and cosmological model.
