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Title: Dynamics of galactic gas streams and satellites
Author: Jin, S.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2008
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The halo of the Milky Way galaxy hosts a substantial quantity of neutral and ionised gas in the form of complexes with large angular extents. Many of these have anomalously large velocities that cannot be explained in simple models of differential Galactic rotation. These so-called high-velocity clouds, some of which are elongated stream-like structures, have been an enigmatic component of the Galactic halo since their discovery in the mid 20th century. The absence of stars within these objects makes it difficult to determine their distance, without which other physical properties, such as size and mass, cannot be constrained. Our general lack of understanding of their origin stems mainly from these uncertainties. In this thesis, a number of so-called geometrodynamical methods are developed in order to constrain the distances to high-velocity HI structures in the Galactic halo. In the first approach, I develop a method that leads to the successful calculation of the distance to the Magellanic stream, without prior knowledge of where the progenitors (the Large and Small Magellanic Clouds) of the stream lie. This approach is restricted to structures with a substantial elongation, a condition not satisfied by other complexes of high-velocity clouds. In Chapter 3, I therefore investigate how the possibility of associations between different, less extended halo structures may lead to the determination of their distances. For this study, I begin by presenting a technique that enables transverse velocities to be calculated for structures that exhibit at least some degree of elongation, and for which sky positions and line-of-sight velocities are known. Using this velocity information, possible orbits can then be deduced in a distance-dependent manner. The validity of the method is verified through its successful application to the stellar Sagittarius stream. I also find two sets of candidates for possible associations, one between the Sagittarius stream and a high-velocity cloud, and the other between two high-velocity clouds. Chapter 4 then explores the degree to which analytic forms can accurately reproduce orbits within a power-law potential. In the course of these three chapters, I have also investigated the orbital characteristics and dynamics of objects in differing potentials. The penultimate chapter of this thesis describes a different problem, where I investigate the possibility of massive black holes as the dark matter component of dwarf spheroidal galaxies. I find that the heating of the stellar population through two-body encounters with the black holes leads to its rapid expansion. This scenario therefore requires the dwarf galaxy to have been significantly more compact in the past, in which case the mass of the individual black holes is constrained to be less than a few 105M⊙.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available