Constraining the mass of galaxy clusters from peculiar velocities

The problem of accelerated cosmic expansion is arguably one of the biggest puzzles in modern cosmology, and several different theories including dark energy and modified gravity models have been proposed in recent years to explain this phenomenon. The ability to distinguish observationally between these different scenarios is of great importance, and tests of General Relativity on large scales provide a model independent way to achieve this. In this talk I will describe how a fundamental test of GR can be performed using a combination of galaxy dynamics and gravitational lensing, which both act as separate probes of the gravitational potential in galaxy clusters. I will discuss how the dynamical mass of a cluster can be constrained from galaxy peculiar velocities, using a halo streaming model to predict the effective galaxy infall profile, and numerically modelling the redshift space cluster-galaxy correlation function. I will then present the results of testing the robustness of this method on n-body dark matter simulations, which have been populated with galaxies using a halo occupation distribution. I will discuss the potential to constrain cluster dynamical masses using both existing and upcoming galaxy spectroscopic redshift surveys, and also to compare these results with measurements of cluster lensing masses in order to perform a fundamental test of General Relativity.