Insights from spectral stacking on the HI content of cluster galaxies in various environments

This thesis focuses on the neutral gas (HI) content of galaxies in different sub-environments within and around galaxy clusters as a means to investigate the physical processes leading to the observed morphology-density relation. I use a range of multi-wavelength data from optical to radio wavelengths, imaging and spectroscopy, and including data from the Westerbork Synthesis Radio Telescope and the MeerKAT radio telescope, to study two large galaxy clusters, Coma and Abell 2626. Using both newly observed, and existing spectroscopic datasets, I identify sub-structures within Coma and Abell 2626, as well as large scale structure in front of and behind Abell 2626 and discover that Abell 2626 is a richer cluster than previously realised. I use a novel technique called HI stacking to measure the average gas content of cluster galaxies, even where galaxies are not individually detectable. This work paves the way for future studies using similar techniques with the upcoming Square Kilometre Array.