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 deg2 DLS field; the survey is a solid basis for identifying massive clusters of galaxies with redshift z ∼< 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 ∼> 1.7 x 1014 Msun. Four of the eight massive clusters in SHELS are detected in the weak-lensing map yielding a completeness of ∼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.