Observational Evidence for Weak Lensing

A single very deep 10 0 eld has been imaged to r 26. There are 2682 galaxies with 23 r 26 with a size signiicantly larger than the seeing disk in the eld. After correcting for telescope aberrations, possible guiding errors, and signal degradation due to seeing, I nd a polarization signal of amplitude jpj = 2:7%, with an uncertainty of 1.2% (95% conndence limit). For the 1773 galaxies with 23 r 25, the measured amplitude is 2.4% 1.2% (95% conndence limit). If this observed polarization is due to gravitational lensing by large scale structure, cosmological inferences can be made. The polarization amplitude would indicate that 0 8 1. The amplitude probability distribution is a Rayleigh distribution with variance 2 p so the probability P (1=2 < jpj== p < 2) = 75%, and P (1=3 < jpj== p < 3) = 93:5%. The measurement of the polarization amplitude in a single eld can be used to constrain cosmological models since p / 0 8 .