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J.F. Hennawi, V.K. Narayanan, D.N Spergel (Princeton University Observatory), I.P. Dell'Antonio (Brown University), V.E. Margoniner, J.A. Tyson, D. Wittman (Bell Laboratories, Lucent Technologies)
The distortion of images of faint high-redshift background galaxies can be used to probe the intervening mass distribution. This weak gravitational lensing effect can be used to detect dark matter in clusters of galaxies, allowing one to effectively "image" and "weigh" these dark objects. Weak lensing observations from the Deep Lens Survey (DLS) are used to construct the first \emph{mass-selected} sample of galaxy clusters. We introduce a new robust weak lensing statistic that is sensitive to the velocity dispersion of a galaxy cluster, circumventing the inherent ambiguity in defining the cluster mass. This statistic is applied to the DLS data and to weak lensing maps calculated from numerical simulations of the CDM model with different cosmological parameters.
We find that the number of clusters detected and their redshift distribution are very sensitive to the density of matter, \Omegam and the equation of state of the dark energy, w. The degeneracy curve in the \Omegam-w plane is nearly orthogonal to that expected from CMB measurements, so that a combination of CMB data with weak lensing by galaxy clusters will break the degeneracy in these parameters. The planned Large-aperture Synoptic Survey Telescope (LSST) is an 8m class telescope that will repeatedly survey large portions of the sky to unprecedented depth. LSST will observe 1000 sq.deg in multiple colors, yielding 100 million source galaxies out to z=3, and giving rise to a mass-selected sample of over 5000 clusters with known redshifts. We predict that the same analysis applied to the LSST cluster sample will determine w to within a percent, sharply constraining the physical nature of the dark energy.
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