From birth to maturity: tracing the evolution and impact of radio galaxies

We now understand that a supermassive black hole lurks at the centre of nearly every galaxy in the Universe. When the gas surrounding these supermassive black holes starts swirling around them, heating up to very high temperatures before eventually falling in, it leads to a phenomenon called active galactic nuclei (AGN). This is one of the most energetic phenomena in the Universe. In some cases, jets of fast-moving plasma particles are also produced, which are brightest at radio frequencies. These sources are called radio galaxies and are the focus of this thesis. In this thesis, we have studied the lives of radio galaxies and how they interact with the gas around them. We have combined data at radio frequencies from different observatories around the world to understand the evolution of radio galaxies. We investigated the presence of restarted activity in radio galaxies, that is, galaxies where a new phase of activity has started before the older phase has completely faded away. We have also identified a radio galaxy in a merger of galaxies, allowing us to understand how mergers trigger nuclear activity. This has provided new insight into the life cycle of radio galaxies. We also tracked how the impact of radio galaxies on the gas that surrounds the black hole, changed as the AGN evolved from younger to older phases. Our studies have suggested that radio galaxies have the strongest impact on the surrounding gas when they are young, and as they evolve, this impact is reduced