The role of neutral hydrogen in the evolution of nearby radio galaxies

PhD ceremony: Mr. R.C. Struve, 14.45 uur, Academiegebouw, Broerstraat 5, Groningen

Thesis: The role of neutral hydrogen in the evolution of nearby radio galaxies

Promotor(s): prof. J.M. van der Hulst

Faculty: Mathematics and Natural Sciences

Most, if not all, galaxies harbour a super-massive black hole in their centre with masses up to a few billion times the mass of the Sun. In some cases, gas and matter from large distances (>3000 light years) reaches the circumnuclear environment (< a few light years) and feeds the black hole. Such black holes are called "Active Galactic Nuclei" (AGN). During this process, large amounts of radio-plasma can get ejected by jets forming giant radio lobes. Simulations show that mechanical "feedback" from AGN strongly regulates the growth of galaxies. Hence, AGN are crucial for the evolution of their hosts. However, how AGN work in detail and why a black hole becomes active is not yet entirely clear. Nuclear gas reservoirs seem to play an important role. Different mechanisms have been proposed for transporting the gas down to the central region. For instance, gas-rich galaxy mergers and interactions may be particularly important. This thesis examines the importance of cold gas in AGN host galaxies: gas structures at a scale of one million light years are observed in order to investigate the importance of interactions with companion galaxies, the gas disk dynamics is studied on a scale of 100,000 light years in order to search for gas which may be moving inwards, and the circumnuclear environment is probed on a 300 light year scale to address the question whether cold gas is indeed fuelling the AGN. Our results indicate that gas-rich interactions are likely not the main mechanism causing radio activity.