Goad, Michael Robert; (1995) The broad line region of active galactic nuclei: A self-consistent 3-dimensional model. Doctoral thesis (Ph.D.), University College London (United Kingdom).

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Abstract

Emission-line variability has been shown to provide a powerful diagnostic of the geometry, kinematics and physical conditions within the Broad Line Region (BLR) of Active Galactic Nuclei. In order to interpret the available monitoring data, and thereby determine the BLR structure, a sophisticated multi-cloud modelling code 'PROSYN' has been developed. A variety of BLR geometries and velocity fields have been modelled, calculating emission-line response functions, light-curves and trailed spectrograms, assuming both isotropic line-emission and a linear line response to changes in the ionizing continuum. In particular, a detailed study has been made of spherical BLR models comprising ensembles of clouds whose physical properties and spatial distribution are described by radial pressure laws. Individual line-emissivities have been calculated using a photoionization code. Emissivity-weighted and responsivity-weighted response functions have been calculated for a large number of emission-lines covering a wide range in ionization state. Comparison of the response functions of different emission-lines is found to provide a powerful constraint on the run of physical conditions within the BLR. The suitability of certain lines for determining the structure of the BLR is also discussed. It is shown that anisotropic line-emission and non-linear line response to continuum variations, must be taken into account in any realistic model of the BLR. These physical effects drastically alter the shape and intensity of the modelled response functions, emission-line light-curves and time-dependent line profiles. A comparison of the modelled and observed emission-line light-curves of the most frequently monitored AGN reveal that BLR models incorporating both of these effects agree with the observations significantly better than models in which they have been ignored.

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