Substructure

Measuring galaxy cluster total masses and the amount of dark matter substructure within galaxy cluster haloes is a fundamental probe of the ΛCDM model of structure formation, as well as the interactions between baryonic and non-baryonic matter. In this thesis I approach the topic of cluster mass structure in two ways. With a combination of optical imaging, spectroscopy, and X-ray observations I determine that the cluster RCS043938-2904.7, while apparently anomalous initially due to its high optical richness and low X-ray surface brightness, is in fact an association of structures along the line of sight. Accounting for this structure brings the observed cluster properties into agreement with known scaling relations. I also present a novel method for measuring weak gravitational lensing flexion to inform mass measurements on small scales. While previously published methods for measuring flexion focus o