Constraining Modified Gravity Using Galaxy Cluster Dynamics

Modified Newtonian Dynamics (MOND) has successfully reproduced observations on galaxy scales and made several successful, a priori unexpected, predictions therein; however, the theory fails to match observational results on larger scales, specifically in groups and clusters of galaxies. To rectify these tensions, MOND extensions have been proposed in the literature which aim to bring the MOND research paradigm back into accordance with observational findings. Often these extensions add further degrees of freedom to the model, making them difficult to test or refute. In this work, we discuss two popular MOND extensions, MOND + DM, and Extended MOND (EMOND). We aim to utilize the theoretical framework of these extensions in order to predict observable deviations from the CDM paradigm which could serve as observational tests of the MOND extensions in question

To identify constraints on each theory, we utilize its formalism in conjunction with a sample of galaxy clusters analyzed using Chandra data to study the capacity of each theory to correctly describe the complex interplay between the intracluster medium (ICM) and its gravitational potential. We use the assumption of hydrostatic equilibrium (HSE) in the cluster sample to illustrate restrictions on the ICM temperature profiles required by each of the theories studied. We demonstrate that the MOND + DM paradigm can be significantly constrained by the imposition of hydrostatic equilibrium in galaxy clusters and several results are derived to that effect. We show that these constraints could be tested with upcoming X-ray missions, including XRISM. Furthermore, we illustrate significant inconsistencies in the EMOND paradigm which suggest that extension to be non-viable in clusters of galaxies. This work has demonstrated that MOND extensions make refutable predictions which should be detectable with current or upcoming observational technologies; signifying that each of these theories could be tested by observing missions. While the failure of these extensions doesn't necessarily indicate that MOND is an incorrect theory, showing that these extensions fail to produce viable results clearly places the burden of progression on MOND theorists to establish MOND paradigms in which such phenomenology is no longer predicted.