Measuring anisotropic stress with relativistic effects

The distribution of galaxies is a power tool to test our cosmological model. In this talk I will discuss the different contributions that affect the observed distribution of galaxies. I will show that besides the standard density and redshift-space distortions, the number counts of galaxies is affected by gravitational lensing and relativistic effects. I will then discuss how one of these effects, called gravitational redshift, can be used to measure the anisotropic stress, i.e. the difference between the two gravitational potentials, in a model-independent way.