Searching for massive clusters in weak lensing surveys

Abstract

We explore the ability of weak lensing surveys to locate massive clusters. We use both analytic models of dark matter halos and mock weak lensing surveys generated from a large cosmological N-body simulation. The analytic models describe average properties of weak lensing halos and predict the number counts, enabling us to compute an effective survey selection function. We test the model prediction for the peak number counts in weak lensing mass maps against the mock numerical data, and find that the noise due to intrinsic galaxy ellipticities causes a systematic effect which increases the peak counts. We develop a correction scheme for the systematic effect in an empirical manner, and show that, after the correction, the model prediction agrees well with the mock data. The mock data is also used to examine the completeness and efficiency of the weak lensing halo search with fully taking into account the noise and the projection effect by large-scale structures. We show that the detection threshold of S/N=4-5 gives an optimal balance between completeness and efficiency. Our results suggest that, for a weak lensing survey with a galaxy number density of ng=30/arcmin^2 with a mean redshift z=1, the mean number of peaks in the 10sq deg area is N_peak=62 for a detection threshold S/N=4. The contamination rate is 42%, and thus, on average, 36 out of 62 peaks (at least) are signals from real halos. Weak lensing surveys thus provide a reasonably efficient way to searching for massive clusters.