This Thesis explores the use of independent dynamical probes (multiple populations, gravitational lensing) to infer the prope1ties of Dark Matter (DM) haloes and investigate scenarios of galaxy formation. It begins with a study of the virial properties (flattening and global anisotropy) of stellar populations in different DM profiles. General theorems are presented, with some application to the Milky Way potential (DM flattening and density profile) as probed by the thick disk, stellar halo and rotation curve. A powerful outcome of virial methods applied to multiple populations is the distinction between DM cusps or cores in nearby dwaif Spheroidal galaxies, in particular Seu lptor and Fornax. Modelling based upon the Jeans equations is reformulated so that it involves just the direct observables (surface density and velocity dispersion), which enables a simultaneous exploration of photometric and dynamical prope1ties. This is applied to different systems. First, probes of DM in early-type galaxy gravitational lenses are devised and the mass-bias underliying some common assumptions in the literature is quantified. Second, when studying the Globular Cluster (GC) system of the nearby Elliptical M87, this new approach yields information on the GC subpopulations, the luminous mass and DM profile. Inference on the GC orbital structure is discussed, with an eye to the processes of assembly and evolution that my have produced it. The general aim of this Thesis is the development of simple, yet flexible and robust, methods to study DM profiles in spheroidal or ellipsoidal galaxies of different sizes and masses. The combined treatment of photometry and dynamics yields appreciable insight even when the data are not enough to justify more elaborate modelling techniques.

published_or_final_version / abstract / Physics / Master / Master of Philosophy

Thesis (M. Phil.)--University of Hong Kong, 2008. / Also available in print.

Thesis (Ph.D.)--Ohio University, March, 2004. / Title from PDF t.p. Includes bibliographical references (p. 95-101)

X-ray Emission from Low Mass Binary Systems X-ray time-series and spectra of two LMXRBs are presented. The data are from the the well-known X-ray burster MXB1636-536 and the dipping source 4U1624-49. In the case of MXB1636-536, a simultaneous optical observation is also presented. The 2-20 keV persistent X-ray emission from MXB1636-536 is found to show both positive and negative hardness-flux correlations and to vary by a factor of &sim; 2 on timescales of hours. The persistent spectrum is best described by a power law with high energy cut-off, indicative that Comptonization dominates the spectral formation in the inner accretion disk. The temperature, optical depth and Compton y parameter of the Comptonizing plasma are derived; the Compton y parameter shows that the spectrum is consistent with unsaturated Comptonization. The negative hardness-flux correlation is explained in terms of the Compton cooling of a hot neutron star corona as a result of an increase in accretion rate. It is notable that a negative hardness-flux correlation and a power law spectrum is in direct conflict with previous observations of this source. Thirteen X-ray bursts, exhibiting a wide variety of profile, were also observed from MXB1636-536. The peak burst flux and burst fluence varied by a factor of 6 and 5 respectively. The burst sample may be divided into two distinct classes: those with fast rise and high peak intensity (strong) and those with slow rise and low peak intensity (weak). Moreover, the strong bursts are 'super-Eddington' and one of the weak bursts is unusual in that it is double-peaked in both the X-ray and bolometric burst profiles. The observed burst properties are discussed within the framework of the current thermonuclear flash models and other physical scenarios. One of the bursts, observed simultaneously in both the X-ray and optical wavebands, is used to determine the possible locality of the reprocessing region in the accretion disk. 4U1624-49 reveals a pattern of dips in the 1-10 keV X-ray light-curve which repeat with a period of ~21 hours. This is almost certainly the binary period of the system, making it one of the longest binary periods amongst LMXRBs. The &sim;25% residual flux can be associated with a physically extended emission component whereas the dips are associated with the intermittent obscuration of a compact component by material in the line-of-sight. The spectral changes occuring within the dips are complex and indicate energy-independent reductions in flux and substantial increases in absorption. The dips cannot be explained by a bulge at the outer disk edge (at the point of impact with the incoming stream) obscuring the central X-ray source. Assuming the primary of 4U1624-49 is a 1.4M? neutron star, the companion is likely to be an evolved star with a mass < 3M? and radius < 2.75R?. The orbital inclination is found to be within the range predicted by the FKL model for 'pure dippers' i.e. 60° < I < 75°.

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The presence of turbulence in astrophysical magnetic fields can have a significant effect on the diffusion of particles and, therefore, should be taken into account when performing simulations involving particle propagation. After reviewing the constructionof the turbulent magnetic field component, we incorporate this feature in two separate projects. In the first, we consider the possible source(s) of hadronic cosmic rays thought to be responsible for the diffuse TeV gamma-ray emission in the vicinity ofthe Galactic center. Assuming a completely turbulent magnetic field with an average strength of 10-100microG, we find that relativistic protons do not travel far enough to produce gamma-rays spatially correlated with the giant molecular clouds, as seen by HESS,when injected into the interstellar medium by a single point source, such as the supermassive black hole Sagittarius A*. Increasing the number of point sources to five does improve the longitudinal extent of the emission but either shows only weak correlation with the molecular gas or highlights the source positions - both pictures areinconsistent with HESS observations. We conclude that protons must be accelerated throughout the Galactic center region via e.g. a second-order Fermi process in order to reproduce the HESS gamma-ray map if the magnetic field there is completely turbulent. Secondly, we examine the possible link between the asymmetric 511keV electron-positron annihilation emission from the inner Galactic disk and hard low mass X-ray binaries (LMXBs). Three different magnetic field configurations were considered: a completely turbulent field, a field in which the turbulent component has equal energy density as the mean component, and a strongly ordered field with little turbulence. Assuming the environment around each LMXB system is the same, we find that the LMXBs alone cannot account for all the positrons necessary to sufficiently fill the region regardless of the particular magnetic field structure chosen. Another transport mechanism (e.g. a galactic wind) in addition to the diffusive motion caused by the magnetic field fluctuations and/or allowing the LMXBs to be embedded in different phases of the interstellar medium is needed for the LMXB picture to remain a viable possibility.

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