In this thesis we present numerical and analytical models of supermassive black hole (SMBH) feeding, via deposition of gas, in galactic nuclei. Through simulations, we consider the environment of galactic centres, starting at sub-parsec scales within our own Milky Way, and moving upwards in scale and outwards in generality to scales of hundreds of parsecs in typical galaxies and finally to dark matter halos within which galaxies reside. We find that the stellar features observed in our own Galactic centre are likely explained by a collision between two molecular clouds at a distance of a few parsecs from the central black hole, Sgr A*. The amount of gas transported to small radii is large, occurring on a timescale close to dynamical. The disordered nature of the flow leads to the formation of a gaseous disc around Sgr A* that in some cases remains small-scale, undergoing complex, time-varying evolution in its orientation. Such a disc would efficiently feed the SMBH, if replenished from larger scales. We develop a model for ballistic accretion onto an SMBH at the centre of a typical galaxy, from scales of ~ hundreds of parsecs. We invoke turbulence in the gas, assumed to be driven by feedback from supernovae, as the means to create such a flow. The accretion mode is again dominated, soon after the initial turbulent kick, by the dynamical timescale for the gas in the angular momentum loss-cone, resulting in an accretion rate at or near Eddington, >~ 1Mסּ yr−1. At the largest scale, we critically evaluate the current state-of-the-art prescription for SMBH growth in cosmological simulations, finding that in general it lacks a physically consistent basis. We propose an alternative, motivated by our analytical estimates and numerical simulations, that is based on the free-fall time.

In this thesis I present numerical simulations of massive, cold, non-ionised self-gravitating accretion discs about a central massive object, and then use them to investigate structure formation and energy/angular momentum transport, the effects of different cooling regimes on the likelihood of bound condensates forming through direct gravitational fragmentation, and the potential for resolved sub-mm imaging of such systems. I also present a review of current theories of viscous and wave transport in astrophysical discs, observed properties of protostellar and protoplanetary discs and a numerical scheme suitable for conducting computational experiments on fluid discs. I find that the structures excited in self-gravitating fluid discs self-regulate in such a manner that the density waves formed are very weak shocks, with the amplitude of the density perturbations forming the waves determined by the cooling regime. This self-regulation process ensures that for discs of \lesssim 10% of the central object mass the transport properties are determined principally by local effects, representing a crucial difference between collisional (fluid) and collisionless (stellar) discs as the latter cannot form shocks. I further find that the effects of an opacity-based cooling function makes self-gravitating protoplanetary discs significantly more susceptible to fragment formation in certain opacity regimes at relatively high (10−5 − 10−3 M⊙ yr−1) accretion rates due to the dependence on temperature perturbations. Furthermore I find that fragment formation due to direct gravitational collapse is feasible in such discs only at radii \gtrsim 50 AU, and this radius increases with decreasing temperature if the background temperature falls below approximately 10K. Finally I have used simple disc models in conjuction with a realistic telescope model to demonstrate that resolved images of spiral structure in massive, self-gravitating protostellar discs should be readily observable with ALMA, out to distances representative of local star-forming complexes.

In this thesis we have employed plasma and magnetic field data from the Cassini spacecraft in order to better understand Saturn’s ring current region. Three data studies are presented along with a derivation of the general expression for the field-perpendicular current density in terms of the plasma bulk parameters. In the first data study an essentially direct determination of the equatorial current sheet thickness was made using data from six north-south Cassini orbits. The dayside data indicated the presence of an equatorial current disk with a near constant half-thickness of ~1.5 RS. More variable conditions were found on the nightside. The data examined also provided evidence of a northward displacement of the current layer from the equatorial plane. Next, the nature of the ring current in Saturn’s dayside magnetosphere was investigated. The total azimuthal current density was found to rise from small values near ~6 RS, peak at ~100 pA m-2 near ~8 RS, and then reduce to values below ~25 pA m-2 at distances beyond ~15 RS, up to the 20 RS limit of our study. The overall total current density profile was found to be similar to that produced by the pressure gradient current, but augmented in strength by factors of ~1.5-2.0 by the difference between the inertia and pressure anisotropy currents. Comparison of the current density profiles deduced from plasma data with those obtained from current disk modelling of the magnetic field perturbations showed good agreement with the gross features. Finally, both the local time dependency and temporal variability of Saturn’s ring current was explored using data obtained from eleven near-equatorial Cassini orbits. In general, the plasma parameters, azimuthal current, and related magnetic perturbation fields were found to exhibit only modest variations with local time and from pass-to-pass over the interval of this study.

We study the solar wind interaction with Mars and the location, shape, dynamics and controlling factors of the magnetic pileup boundary (MPB) and the bow shock (BS), which form as a result of this interaction, by using single as well as two-spacecraft measurements. By using Mars Global Surveyor (MGS) measurements we produce statistical models of the shapes of the two boundaries. The influence on the boundaries from the crustal magnetic fields of Mars is also studied. We find that the MPB is pushed to higher altitudes depending on the strength of the underlying crustal fields while the BS is found at higher altitudes over the entire southern hemisphere of Mars, where the crustal fields are strongest. By using the simultaneous measurements from Rosetta and Mars Express (MEX) we study the boundaries during high and low solar wind dynamic pressure. During low pressure, simultaneous two-spacecraft measurements provide leverage on the accuracy of the shape of the MPB and BS. Their previously modelled shapes are found to be in agreement with the shapes derived from these two-point measurements. During high pressure, we observe how the boundaries become asymmetric in their shapes, possibly due to increased plasma outflow over one hemisphere, which lowers the plasma pressure on that side of the planet and results in an asymmetric shape. By using MGS and MEX measurements we study the altitude of the boundaries as functions of solar wind dynamic pressure, solar EUV flux and crustal magnetic field strength. We also examine the effect of the direction of the interplanetary magnetic field on the boundaries. We find that the dynamic pressure, EUV flux and crustal magnetic fields are the main governing factors of both the MPB and the BS.

We have studied the extended X-ray emission observed in the disks of seven nearby face-on spiral galaxies using XMM-Newton archival observations. Using a novel technique to remove the bulk of the contamination from bright X-ray point sources, we have isolated a residual disk component in each galaxy, comprising diffuse gas plus the integrated population of faint point sources. We have found soft X-ray emission from this component to be strongly correlated with FUV emission, unambiguously establishing a close link with recent star formation. We have found the residual X-ray/star formation rate (SFR) ratio across our sample to range from 1-5x10^39 erg s^{-1} ( M \odot yr{-1})^{-1}, with the ratio highest in regions with the highest SFR. This is consistent with the models of Ranalli et al. (2003), and matches the predicted X-ray emission ≈ 10 Myr after an extended burst of star formation. Our spectral analysis of the residual disk components indicates that a two-temperature thermal plasma fits the data well, with derived temperatures of 0:2 keV and 0:65 keV. This is consistent with previously derived results for spiral and starburst galaxies (e.g. Fraternali et al. 2002). We have shown the emission to be well modelled by a clumpy thin-disk distribution, with bubbles of hot gas and collections of faint point sources tracing the galactic spiral arms. We have found the excised bright point source populations to be evenly divided between old and young sources with the exception of M33, where young sources dominate. We have derived the residual X-ray/mass ratio in the inner disk of this system to be be 4x10^{28} erg s^{-1} M\odot^{-1} This is 5-10 times higher than the equivalent ratio in low star formation rate systems (Revnivtsev et al. 2008), with the excess attributed to contributions from the young point source population and diffuse gas. Our results have demonstrated a quantifiable link between diffuse X-ray emission and recent star formation in spiral galaxies. Further study is necessary to better constrain this relationship, in particular its dependence on the local environment.

This thesis presents a study of a sample of objects with a high X-ray-to-optical flux ratio, which are believed to be a good tracer of highly obscured, high redshift active galaxies (AGN). Such objects have particular importance since they may account for a significant fraction of the accretion history of the Universe and because of their links with the co-evolution of super-massive black holes and their host galaxies. In this thesis the results are presented for a new sample of bright, X-ray selected objects with extreme X-ray-to-optical flux ratios (“EXOs”), constructed from a cross-correlation of the 2XMMp X-ray and the SDSS-DR5 optical catalogues. Investigation of the optical/NIR and X-ray colours constrains the fraction of obscured sources to be over half of the sample. Optical and X-ray spectroscopic analysis for a sub-sample of the EXOs confirms these results and reveals the presence of a large number of type-2 QSOs. The discovery of the source with the currently highest X-ray-to-optical flux ratio value is also reported and its properties investigated. Finally, a population study of a complete sample of bright X-ray selected AGN from the Subaru/XMM-Newton Deep Survey (SXDS) is presented. Through detailed X-ray spec- tral analysis, the average properties of the sample are investigated and the fraction of absorbed sources and its dependence on the intrinsic X-ray luminosity is studied. The properties of the high X-ray-to-optical flux ratio sources in this SXDS sample is compared with the EXO sample drawn from the the 2XMMp/SDSS catalogue cross-correlation.

Measuring the effect of geological and chemical processes, weather, biological processes and the interaction of SCR and GCR radiation with a planet is fundamental to understanding the formation, evolution and alteration of a planet. This thesis details the evolution and development of a geophysical package that can be used to better understand the effect of these fundamental physical processes by measuring composition, constraining heat flow and measuring the age of a planetary surface. There are a number of future ESA and NASA planetary science missions that are in the planning or initial study phases, where the scientific objectives include determining the surface composition, measuring planetary surface heat flow and constraining planetary chronology. The geophysical package is capable of operation on landers and penetrators; both of these are possible in-situ platforms being proposed for these missions. In addition radioisotope power sources are being proposed for both thermal management and electricity generation; the power source might provide the source of neutrons to induce the γ-ray emission from the planetary surface. The development and verification of a Monte Carlo planetary radiation environment model using both experimental data and data acquired in orbit of the Moon and Mars is described in this thesis. It was used to model the geophysical package on the surface and sub-surface of Mars and Europa. The model was also used to investigate the suitability of several neutron sources to induce γ-ray emission on a planetary surface that could also be used for power generation.

Dwarf Spheroidal galaxies (dSphs) are the nearest and the most dark matter dominated galaxies in the Universe. In this thesis, we study their kinematics and dynamics using Monte Carlo methods. First, we study the kinematics of stellar subpopulations in dwarf spheroidal galaxies and present a robust Monte Carlo based method for interpretation of the sub-population data in dSphs. We apply the mehod to new spectroscopic data for twenty six stars in the recently-discovered Canes Venatici I (CVn I) dSph, obtained with the GMOS-N spectroscope on the Gemini North telescope. We use these data to investigate the recent claim of the presence of two dynamically different stellar populations in this system (Ibata et al., 2006). While we find no evidence for kinematically distinct sub-populations in our sample, we also show that the available kinematic data sets in CVn I might be too small to draw robust conclusions about its sub-populations. Second, we introduce a Markov Chain Monte Carlo based method for studying the dynamics of dSphs. We perform a large number of N-body simulations of the Carina dSph, modelling it with different dark matter halo profiles in the presence of tidal interactions. We show that due to the uncertainties in the data, it is possible to find several good models that can match Carina’s observed data. We show the differences in the mass, density, compactness and orbital eccentricities that result from different split power halo profiles, as well as mass follows light models. Finally, using high resolution re-simulations of some of our best models, we show the robustness of our results and perform a more detailed analysis of the models, looking at their mass evolution, and general tidal signatures that should be looked for in future observations.

This thesis describes both theoretical and experimental work conducted to further develop X-ray instrumentation for future planetary and astronomy space missions. Such instruments are used to probe, ever deeper, the high energy Universe; from black holes and active galactic nuclei, to supernovae, galaxy formation and clusters. X-rays can also be used to establish the elemental composition of planetary surfaces from orbit or in situ, furthering our understanding of planetary and moon formation in our solar system. Chapter 1 introduces X-ray instrumentation and uses the International X-ray Observatory as a case study to explore the many new developments in X-ray instrumentation, both in optics and detectors. Chapter 2 further explores the field of X-ray optics, particularly the novel Microchannel Plate Optics used on the BepiColombo Mercury Imaging X-ray Spectrometer, MIXS. The characterisation of an MCP optic is presented, demonstrating the best angular resolution measurement of a flat square-pore square-packed Microchannel Plate Optic to date; <2 arcminutes FWHM resolution. Chapter 3 moves from the X-ray optics used on BepiColombo MIXS to the detectors used in the instrument focal plane; Active Pixel Sensor Depleted Field Effect Transistors (DEPFETs). The solar proton radiation environment around Mercury is one of the most damaging in the solar system due to its proximity to the sun, with ~3x1010 10 MeV equivalent solar protons expected over the mission lifetime. This Chapter presents the proton radiation damage experiments conducted at the Birmingham University Cyclotron, establishing the current related damage rate, α, and dark current increase that can be expected from this radiation damage. The design of the MIXS instrument was changed to include an annealing capability based on the findings of the experiment presented here. A follow-up proton irradiation experiment carried out at the University of Technology in Munich, in collaboration with the Max Planck Institute’s Semiconductor Laboratory (MPE-HLL) is also discussed. Chapters 4 and 5 present the experimental and modelling work carried out in the investigation of X-ray CCDs which, to date, have been the X-ray detectors of choice for many space and terrestrial applications. The aim of this work was to improve the quantum efficiency and spectral resolution of the CCD66, a novel CCD structure initially designed with applications such as the Wide Field Imager of the International X-ray Observatory in mind, by direct manipulation of the device depletion region by applying a negative substrate voltage. Modelling work was also undertaken to investigate the effect of X-ray angle of incidence on spectral resolution and quantum efficiency. The future of X-ray astronomy and planetary science depends heavily on advances in optics and detector technology. The work presented in this thesis show incremental, yet mission-enabling developments for X-ray instruments likely to fly in the future such as BepiColombo’s Mercury Imaging X-ray Spectrometer.

This thesis uses the data from twenty ROSAT and XMM observations to investigate the structures that generate the soft X-ray background of the Milky Way. Ten of these observations lie in the direction of the Loop 1 Superbubble, specifically, within the North Polar Spur, the Northern Bulge, and immediately south of the Galactic Plane. The others are located in the Anti-centre direction, where the X-ray background is less complex. Using a novel processing technique, point sources and enhancements were successively removed from the observations until only the Diffuse X-ray Background (DXRB) re¬mained. By modelling the spectra of this clean data, and separately analysing the 0 and 0 viii emission lines, the various structures in the DXRB were identified, and their properties determined. The resulting models strongly indicate the existence of three previously unidentified components: a 14 pc thick, 0.1 keV shell surrounding Loop I, an inhomogeneous 0.25 keV Galactic Halo, and a non-thermal component present in the Galactic Centre direction. In contrast with previous work, no evidence was found for a cool Galactic Halo. The centre of Loop I was placed 290 pc away, 80 pc farther than previously believed. Additionally, an ongoing interaction was discovered between the Local Hot Bubble and Loop I.