| Weak gravitational lensing induced by large-scale structure has emerged as a powerful tool for probing the mass distribution in the Universe. We present our measurement of this so-called "cosmic shear" signal in the linear part of the mass power spectrum using the large-area radio survey, FIRST. To measure accurately source shear with interferometric data, we develop a new method to model simultaneously all sources in each field observed directly in Fourier space, using Gauss-Hermite orthonormal basis functions with a least-squares fit. The method, outlined in Chapter 2, is linear and yields unbiased shear estimators. In Chapter 3, we apply the method to the FIRST data covering 8,000 square degrees of the sky. After carefully correcting for the crucial systematic effects, modeled by realistic simulations, we detect a cosmic shear signal on angular scales of 1°--4° at the 3.8-sigma level. We constrain the combination of parameters, sigma8(zm/1.5) 0.6, to be 0.99 +/- 0.26, where sigma8 is the mass power spectrum normalization on the 8 h-1 Mpc scale, and zm is the radio source median redshift. The error includes statistical errors, cosmic variance, and systematic errors. Our result is consistent with the sigma8 constraints from other cosmic shear measurements and from WMAP, as well as with general knowledge of the radio source redshift distribution. Our measurement is complementary to all previous cosmic shear experiments, it provides an independent confirmation of the shear induced by the large-scale mass distribution in the Universe, and opens a new approach to cosmic shear studies. |
