Searching for Dark Matter Halos in the Suprime-Cam 2 Square Degree Field

We report the first result of a weak gravitational lensing survey on a 2.1 deg2 Rc-band image taken with a wide-field camera (Suprime-Cam) on the prime focus of the 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 ≥ 1014 M☉. The reconstructed convergence field is divided by 1 σ noise to obtain the signal-to-noise ratio (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 is created to compare with model predictions. We found excess over noise PDF created from the randomized realization on both the 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 deg2 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 Navarro-Frenk-White halo profile under the cluster-normalized cold dark matter cosmology. Although the present statistics are not enough because of 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 the cosmological model.