Weak‐Lensing Discovery and Tomography of a Cluster atz= 0.68

We report the weak lensing discovery, spectroscopic confirmation, and weaklensing tomography of a massive cluster of galaxies at $z=0.68$, demonstratingthat shear selection of clusters works at redshifts high enough to becosmologically interesting. The mass estimate from weak lensing, $11.1 +- 2.8 x10^{14} (r/Mpc)$ solar masses within projected radius r, agrees with thatderived from the spectroscopy ($\sigma_v = 980 km s^{-1}$), and with theposition of an arc which is likely to be a strongly lensed background galaxy.The redshift estimate from weak lensing tomography is consistent with thespectroscopy, demonstrating the feasibility of baryon-unbiased mass surveys.This tomographic technique will be able to roughly identify the redshifts ofany dark clusters which may appear in shear-selected samples, up to z ~ 1.Comment: Final version. Substantially expanded from first version, including more detail, more figures, and more mass estimates, including an M/L estimate. Basic conclusions unchange