SHELS: TESTING WEAK-LENSING MAPS WITH REDSHIFT SURVEYS

Weak-lensing surveys are emerging as an important tool for the construction of mass-selected clusters of galaxies. We evaluate both the efficiency and completeness of a weak-lensing selection by combining a dense, complete redshift survey, the Smithsonian Hectospec Lensing Survey (SHELS), with a weak-lensing map from the Deep Lens Survey (DLS). SHELS includes 11,692 redshifts for galaxies with R <= 20.6 in the 4 deg(2) DLS field; the survey is a solid basis for identifying massive clusters of galaxies with redshift z less than or similar to 0.55. The range of sensitivity of the redshift survey is similar to the range for the DLS convergence map. Only four of the 12 convergence peaks with signal to noise >= 3.5 correspond to clusters of galaxies with M greater than or similar to 1.7 x 10(14) M-circle dot. Four of the eight massive clusters in SHELS are detected in the weak-lensing map yielding a completeness of similar to 50%. We examine the seven known extended cluster X-ray sources in the DLS field: three can be detected in the weak-lensing map, three should not be detected without boosting from superposed large-scale structure, and one is mysteriously undetected even though its optical properties suggest that it should produce a detectable lensing signal. Taken together, these results underscore the need for more extensive comparisons among different methods of massive cluster identification.