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Session 83 - Gravitational Lensing.
Display session, Friday, January 09
Weak gravitational lensing by large-scale structure produces distortions in the images of distant sources. This effect can be used to probe directly the spectrum of density inhomogeneities in the Universe. We present our attempt to detect this effect with the VLA FIRST radio survey which currently contains about 400,000 radio sources over nearly 4300 square degrees, and thus provides a unique resource for this purpose. We search for correlations in the ellipticities of resolved sources by considering the ellipticity correlation function, the ellipticity power spectrum, and a global maximum-likelihood estimator. We pay particular attention to systematic effects which can introduce spurious spatial correlations in the source ellipticities. The most serious systematic effects are those produced by the anisotropy of the VLA beam, and by the spatial correlation of the noise in the survey maps. We compare our measurements with the signal expected in various cosmological models. We show how our measurements constrain the power spectrum of weak-lensing distortions on scales from 1 to 100 Mpc.
The FIRST project is supported by grants from the National Geographic Society, the National Science Foundation, NATO, IGPP, Columbia University, and Sun Microsystems.
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