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R. M. Jarvis, G. Bernstein (U. Michigan)
Weak lensing has recently become a powerful technique for studying dark matter on large scales. Most field lensing studies so far have been limited to fields of up to a few square degrees. Here, we present the results of a weak lensing analysis of 80 square degrees of sky observed using the 4m Blanco Telescope at CTIO. The data were taken in 12 well-separated fields, each approximately 2.5 degrees square. In each field, we have shape measurements for about 150,000 galaxies, typically observed 3 times each. The median redshift of these galaxies is z \approx 0.3. This means the lensing dark matter is at z \approx 0.15, for which 2.5 degrees corresponds to a physical scale of \approx 25 h-1 Mpc. Analysis of the data give constraints on \Omega and \sigma8 based on the shape of the power spectrum in the range from 1' to 150'. Systematic errors are a significant problem for weak lensing investigations, especially field lensing, since the direction of the signal is arbitrary. Therefore, we also present several metrics which demonstrate that we have managed to reduce these errors to well below the level of our signal. We thank the NOAO for providing support for travel to CTIO for the observations and we thank the NSF for funding some of the analysis.