Testing Gravity with Galaxy Clusters

Clusters of galaxies are the largest gravitationally bound objects in the Universe and provide a unique laboratory for testing theories of gravity. Our team has pioneered the technique of comparing different tracers of the cluster gravitational potential to place tight constraints on possible deviations from General Relativity (GR) on cosmological scales. This thesis will build upon our previous work in three new areas. First, we will expand the quality and quantity of cluster data available through our proprietary access to the Dark Energy Survey (DES; www.darkenergysurvey.org) and extended X-ray catalogues. We will also explore the use of public KIDS lensing data. Secondly, we will add new cluster tracers (beyond lensing and X-ray), including Sunyaev-Zel'dovich (SZ) pressure maps of DES clusters and velocity dispersion profiles from on-going galaxy redshift surveys. Finally, we will explore a wider range of modified gravity models (e.g. emergent gravity, beyond horndeski, extended tensor-scalar) and continue to improve our N-body simulations for such theories. We will also build better mock observations from these simulations by adding the SZ effect and individual (mock) galaxies to the dark matter halos. Together, we expect this work to improve present constraints on deviations from GR by at least an order of magnitude, providing the best evidence yet for the suitability of GR on cosmological scales (or not!). The thesis will also look beyond present data-sets to new constraints from the next generation of astronomical surveys from Euclid, LSST and 4MOST.