Theoretical and computational models of active galactic nuclei

This thesis discusses the origin of the broad emission lines seen in active galactic nuclei (AGN), in the context of a disc-wind model. An out-flowing nuclear wind generates Kelvin-Helmholtz instabilities within the atmosphere of an accretion disc, which surrounds a super-massive (~ 3 x 10 7 M⊙ ) black hole. The broad line region (BLR) clouds are a direct result of this interaction.;The BLR clouds reach velocities required to explain the broad-bases of the permitted lines, within a few sound crossing times, and are destroyed on a similar time scale. We examine NGC5548, and NGC4151 in detail, and conclude that both sources have a small inner BLR radius (1016 cm). By using near simultaneous CIV and Hbeta profiles of NGC.5.548 it is possible to examine the optical and UV spectral regions simultaneously. Observed continuum light curves were used to predict line light curves. Comparisons with observation indicate that the inner and outer BLR radius, ionisation parameter, column and particle density, for both sources are plausible.;I examine NGC4151 in detail, particularly the CIV line. The line probably comprises more components than the simpler configuration in NGC5548. For example, reflection of CIV line photons off of a surface subtending a solid angle larger than 2pi, can explain the excess flux in the long-wavelength side of the line, and why this is seen to respond before the short-wavelength side, without invoking in-falling clouds. It is possible to rule out the BLR clouds as directly responsible for the UV absorption. However, the cloud-wind interaction is shown to provide a source of highly ionised, low-column density material, that could be the source of UV absorption. This material covers a large solid angle, which implies that a significant fraction (~ 30%) of Seyfert-1s should show an absorbing component.