Gravitational lensing from large scale structure along the line of sight to distant magnifies and shears their images. The shearing pattern is tangential to mass concentration seen in the convergence. Correlations between the ellipticities of galaxies can be used to reconstruct the projected mass along the line of sight.
The two dimensional nature of cosmic shear can be partially overcome. Galaxy sources at various distances are lensed by the foreground mass only allowing tomographic reconstruction. Here the auto and cross power spectrum of the shear in different distance or redshift bins are shown.
Cosmic shear measurements as a function of source redshift can probe the impact of dark energy on the growth of structure and test gravitational explanations of cosmic acceleration.