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Winds in active galactic nucleii.

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thesis
posted on 19.11.2015, 09:17 by Mark D. O'Reilly
This thesis is concerned with a number of problems relating to mass outflow in active galactic nucleii. A number of authors have discussed radiation pressure driven winds, and some have discussed the spectral evolution in such a wind, but under restricted conditions, e.g. the radiation spectrum is thermal at high frequencies. A number of authors have discussed the Comptonization of an arbitrary input spectrum in a stationary medium. In Chapter 2, I consider the evolution of an arbitrary input spectrum by a supercritical outflow. I consider outflows that contain a number of e pairs, these flows are supercritical for modest mass outflows. I find that the input spectrum is not significantly distorted, but that the high frequency cut off moves to a lower frequency. There is a major flaw in the model: most of the radiation energy is carried by photons of energy larger than 0.5 MeV; however, the Kompaneets equation, which is central to the model, is not valid for photons of this energy. There is also an indication that pair production is an important process in the inner regions of the system, a process which has been ignored. The second problem is concerned with the broad line region. The 'standard model' requires a two-phase equilibrium between a hot intercloud medium and cool clouds. This is incompatible with the radiative heating implied by observed spectra. In Chapter 3, I introduce generallised two body heating into the intercloud wind. I find that both the dynamics and thermal equilibria of the system are compatible with the observed velocities of broad line clouds confined by an outflowing medium at 109 K. Many BLR theories require the presence of a wind, probably created in the nuclear region. Variability observations suggest that the X-ray spectrum is also created in this region, this spectrum is often described as a universal power law. It is unreasonable to assume that this ubiquitous slope can be produced by arbitrary tuning of the input parameters. In Chapter 4, I describe a model where the wind dynamics and spectral slope are related: the disk atmosphere is heated by UV radiation and by injected e pairs, causing it to form a wind. The mass loss limits the optical depth of the atmosphere and hence the evolution of the X-ray spectrum, so that the system is tuned by the dynamics to produce the canonical power law. Unfortunately, some of the approximations used in the model produce a set of equations that severely limit the range of physical parameter space that may be sensibly investigated, one or more of these approximations must be relaxed for the model to be of greater use.

History

Date of award

01/01/1995

Author affiliation

Physics and Astronomy

Awarding institution

University of Leicester

Qualification level

Doctoral

Qualification name

PhD

Language

en

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