A new observable for cosmic shear

In this paper we introduce a new observable to measure cosmic shear. We show that if we can measure with good accuracy both the orientation of a galaxy and the polarisation direction of its radio emission, the angle between them is sensitive to the foreground cosmic shear. Even if the signal-to-noise ratio for a single measurement is expected to be rather small, the fact that all galaxies in a given pixel are subject to the same shear can be used to overcome the noise. An additional advantage of this observable is that the signal is not plagued by intrinsic alignment. We estimate the SNR for the shear correlation functions zeta +/-(mu, z(1), z(2)) measured in this way with the future SKA II survey.