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Title: Cold gas in clusters of galaxies
Author: Basson, J. F.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2003
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The intracluster gas has only been fully explored in the last decade or so with the launch of the ROSAT satellite in 1990, and more recently the Chandra and XMM-Newton satellites in 1999. The data obtained from these X-ray telescopes has provided significant information about the intracluster medium. In this thesis, a theoretical and numerical study of the nature of the ICM is undertaken. In particular the formation and influence of cold gas clouds and the effects of powerful FR-II radio sources are considered. Clusters are modelled as a multi-phase cooling gas in a dark-matter potential well. The formation of cold gas clouds through the thermal instability is studied, as is the effects of shocks on cold clouds. The latter is important because of the alignment effect which implies that the presence of a radio source increases the luminosity of the clouds. Radio sources which occur as a result of feedback from the accretion of the cooling intracluster gas onto a central AGN have a noticeable effect on the energetics of the cluster. Observationally, they manifest themselves as cavities in the X-ray emitting ICM. Whether they are capable of halting the inflowing cooling ICM depends on the relative powers of the cooling flow and radio source. The jets expand supersonically into the ICM, heating and dragging the cluster gas out of the potential well. As this shocked gas rises, it cools adiabatically. As it falls back inwards, it forms a layer of cooler gas around the cocoon. The ICM gas is thermally unstable, and the contact discontinuity will be Rayleigh-Taylor unstable provided that its deceleration does not exceed the gravitational force. Coupling between the Rayleigh-Taylor and thermal instability modes can occur, and it is found that the growth rate increases over the individual uncoupled rates when they are of the same order of magnitude. This could provide a mechanism for the information of cold clouds around this interface.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available