Ultraviolet line-driven disc winds as a feedback mechanism in bright active galactic nuclei

Abstract

Astronomical observations have shown that galaxies and the supermassive black holes (BH) located at their centres have evolved together over cosmic time. BH grow by accreting matter from their surroundings and the gravitational potential energy released by the infalling matter can power the enormous luminosities we see in active galaxies and quasars, and is in principle sufficient to significantly disrupt the structure of the host galaxy. However, the particular physical processes through which such active galactic nuclei feedback affects the host galaxy are still poorly understood. One possibility is that the accretion process powers winds that travel through the galactic bulge, displacing the gas reservoir and thus quenching star formation in the galaxy. There are various mechanisms that could drive such winds. In this thesis, we focus on the study of UV line-driven winds originating from the surface of accretion discs, which are driven by radiation pressure on spectral lines and are also present in hot stars. We develop a numerical simulation method for the study of such systems, building up on existing models and incorporating modern computational techniques to study the conditions under which these winds can be launched and accelerated. The resulting model, called Qwind, features relativistic corrections to the radiation flux, as well as an algorithm to perform ray tracing on axisymmetric geometries. We also develop a model to compute the initial conditions to launch the wind from the surface of the accretion disc, based on theoretical frameworks employed in the study of O-star winds. Using this new model, we are able to investigate the dependence of the wind properties on the BH mass, mass accretion rate, and the innermost launching radius of the wind, thus deriving the amount of momentum and energy carried by the wind for different AGN systems.