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|Title:||Hydrodynamics of emission line clouds in active galaxies.|
|Authors:||Foulsham, Paul Anthony.|
|Presented at:||University of Leicester|
|Abstract:||In this thesis we examine the evolution of emission line clouds via hydrodynamic modelling using a Godunov-type code which incorporates a simple radiative heating- cooling function. The results of this are used as the input to a photoionisation calculation from which we obtain emission line ratios and profiles. This allows comparison to observation. In the narrow line region we examine the "catapult model" which suggests that line broadening is a result of clouds falling under the influence of gravity into a nuclear supersonic wind. Larger clouds continue to fall in, whereas smaller clouds have their direction reversed and are ejected. We model the evolution of one of the smaller clouds and find that contrary to the "catapult model" the cloud is destroyed on the order of a sound-crossing time without any significant deceleration, and thus cannot reproduce observed line profiles. If the clouds are inflowing under the influence of gravity, this suggests that we turn our attention to the acceleration region, independent of any destruction process. We find that the thermostatic effect of radiative cooling stabilises the cloud against mass loss. We argue that non- adiabatic clouds may survive of the order ~ 100 sound-crossing times. This is what we require if the narrow line region consists of ~ 104 clouds. In the broad line region we examine the "energy budget problem". The possibility that shock-heating may provide an additional source of energy input to this region is investigated. The results suggest that the high ionisation lines may be enhanced by this process.|
|Rights:||Copyright © the author. All rights reserved.|
|Appears in Collections:||Theses, Dept. of Physics and Astronomy|
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