Dr. Tzu-Ching Chang
Title: Cosmic Shear Measurement with FIRST
Date:
We present the first measurement of weak lensing by large-scale structure on 1-4 degree scales based on the FIRST Radio Survey, a quarter-sky, 20-cm survey produced with the NRAO Very Large Array (VLA). The large angular scales provide an unique measurement in the linear regime of the matter power spectrum. We use the shapelet method to estimate the shear of radio sources derived directly from the Fourier (uv) plane. On 1-4 degrees scales, we find that the aperture mass statistics B-modes are consistent with zero, and detect a lensing E-mode signal significant at the 3.0 sigma level. After removing radio sources with an optical counterpart, the E-mode signal increases by 10-20%, as expected for a lensing signal derived from more distant sources. We constrain the mass power spectrum normalization sigma_8 and the median redshift z_m of the unidentified radio sources. We find sigma_8*(z_m/2)^(0.6) ~ 1.0 +/- 0.2, where the 1 sigma error bars include statistical errors, cosmic variance, and systematics. Taking the prior sigma_8 = 0.9 +/- 0.1 (68%CL) from the WMAP experiment, this corresponds to z_m = 2.2 +/- 0.9 (68%CL) for radio sources without optical counterparts. Our results offer promising prospects for precision measurements of cosmic shear with future radio interferometers such as LOFAR and the SKA.