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We report the discovery of a cluster of galaxies via its weak gravitational lensing effect on background galaxies, the first spectroscopically confirmed cluster to be discovered through its gravitational effects rather than by its electromagnetic radiation. We have confirmed this cluster with spectroscopic redshifts of fifteen members at z=0. 276, with a velocity dispersion of 615 km/s. This fundamentally new selection mechanism promises to yield mass-selected, rather than baryon or photon-selected, samples of these important cosmological probes. We use the shear as a function of source photometric redshift to estimate the lens redshift independently and find zₗ = 0. 30 +- 0. 08. The good agreement with the spectroscopy indicates that the redshift evolution of the mass function may be measurable from the imaging data alone in shear-selected surveys.
Wittman et al. (Mon,) studied this question.
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