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J. A. Tyson (Bell Labs, Lucent Technologies), I. P. Dell'Antonio (NOAO/KPNO), D. Wittman, D. Kirkman (Bell Labs, Lucent Technologies), G. Bernstein (U. Michigan)
Wide-field CCD mosaics on large telescopes now allow for direct surveys for mass concentrations. Weak gravitational lensing of the \approx 60 faint background galaxies per square arcminute creates a shear distortion pattern which can be transformed into a map of projected mass density. In a pilot survey using the Big Throughput Camera on the Blanco 4m telescope at CTIO, we have discovered several clusters of galaxies via this technique of gravitational lens mass tomography. Free of baryon bias, this new view of the universe will permit direct tests of the predictions of cosmological models.
We show a color mural of one of our ``blank" fields for which we have deep images in several bands. 150,000 distant galaxies are seen in a half-degree field. Using the stars in the field to correct for low level shear systematics, we measure the shear induced by foreground mass concentrations at redshifts 0.2-0.6. The resulting mass map is shown. A large scale imaging survey of this kind would measure for the first time the change in large scale structure from z=1 to the present epoch, and test the current theories of structure formation, which predict that mass in the low-redshift Universe has a particular filamentary/sheetlike structure. These unique observations will constrain the clustering properties of matter, most notably \Omega\rm matter and \Omega\Lambda, and, when compared with the results from microwave background anisotropy missions, will test the basic theory of structure formation via gravitational instability.
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