A multifaceted view of the interplay between gas and radio AGN

Abstract

The supermassive blackholes inhabiting the centres of massive galaxies become active galactic nuclei (AGN) when the ambient matter gets accreted onto them. This results in the emission of enormous amount of energy which influences the evolution of their host galaxies. In radio-loud AGN, the energy is emitted in the form of collimated jets. These jets and the ambient interstellar medium (ISM) interact and affect each other: while the radio jets make the ISM turbulent and drive fast outflows, a dense ISM slows the growth of these radio jets. Understanding the nature of this jet-ISM interaction and its evolution with redshift is crucial to understand the role of radio AGN in galaxy evolution.In this thesis, we carried out a detailed study of the interaction between radio jets and the cold ISM: atomic (HI) and molecular, in a low-luminosity radio galaxy using the Very Large Array (VLA), European VLBI Network (EVN) and NOrthern Extended Millimeter Array (NOEMA). This resulted in the first discovery of a massive molecular-gas outflow in this AGN, driven single-handedly by radio jets. This showed that kpc-scale jet-ISM interaction in such sources is important for models of galaxy evolution. We further searched for HI in samples of radio AGN at higher redshifts and suggested that the incidence and kinematics of HI in radio AGN does not evolve up to z ~ 0.4 and provided the first evidence for the evolution of cold-gas content in radio AGN environments at z>0.7