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Title: Gas dynamics in the galactic center
Author: Ridley, Matthew
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2018
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In this thesis we examine several aspects of the dynamics of the interstellar medium at the centre of the Milky Way. The gas is an excellent dynamical tracer: models of the gas response to an externally imposed barred potential place unique constraints on the Galaxy's matter distribution. We show how a simple two-dimensional model of gas flow in a rigidly rotating barred potential provides a convincing explanation of many of the features observed in the (l, b, v) distribution of molecular emission lines at Galactic longitudes |l| < 5°, within the so-called "central molecular zone" (CMZ). In particular, we show that the central gas disc develops a twoarmed spiral, which, in projection, naturally explains two of the dominant elongated emission features. We compare our model against competing explanations for these features in the CMZ and make predictions for future observations. We investigate the general behaviour of gas flow in realistic self-consistent barred N-body models and nd that, in contrast to previous work, the potential is sufficiently smooth and regular that the gas quickly settles into an equilibrium conguration. We show that simple rigid-potential models can be constructed that give good qualitative matches to the gas flow in the live, self-consistent potential. We provide guidance on how best to apply methods that attempt to constrain the Galaxy's potential by tting features in the (l, v) distribution semi-automatically. Finally we discuss the vertical dynamics of the central gas disc in our simulations. We nd that the central gas disc in our models almost exactly follows ballistic orbits. If tilted out of the plane of the galaxy the normal vector to the gas precesses in the opposite sense to the circulation of the gas as a simple consequence of epicyclic theory. Our simulations do not reproduce the observed magnitude of the tilt of the CMZ, suggesting that something other than gravitational forces are responsible for tilting the gas out of the Galactic plane.
Supervisor: Magorrian, John Sponsor: Science and Technology Facilities Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available