Year

1996

Degree Name

Doctor of Philosophy

Department

Department of Physics

Abstract

Several problems concerning the behaviour of gas during structure formation in the Universe are investigated. The beta problem concerns the relative distributions of gas and gravitating matter in clusters of galaxies. One-dimensional self-similar simulations of cluster collapse are used to investigate whether the different colhsional properties of the gas and gravitating matter in clusters can significantly affect their relative distributions. These models can produce beta values similar to those observed. Data for the beta problem are considered next. Beta is found to correlate with cluster temperature. This trend can be explained by a fixed specific energy excess in the gas, but simple modelling shows that the range of excesses required by the data is large. The energy excess can be a significant fraction of the total specific energy of the gas. Possible mechanisms for the excess are considered in the light of these results. A new axisymmetric A^-body/hydrodynamic code is outlined. The axisymmetric code gives better resolution than 3-dimensional codes using the same number of particles. The axisymmetric code is adapted to study the collapse and formation of disk galaxies. This code includes the effects of shock heating, radiative cooling, shear viscosity and mass deposition. Radiative cooling within shocks is shown to be a severe problem in numerical simulations of galaxy collapse. The collapse code is used to simulate galaxy formation following the model of Nulsen & Fabian (1995). The disk galaxies formed during these simulations resemble observed spirals, with fiat rotation curves and exponential surface densities, but the disk masses are low. The disks are formed from radiatively cooled hot gas and so form later than in previous models. The low disk masses are, at least in part, due to problems of simulating radiative coohng.

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