This thesis presents three higher-mass star forming regions (Mon R1, Mon R2 and NGC 2264) as observed by Herschel, and also the JCMT (SCUBA-2), and the IRAM 30-m telescope, with additional data from the Spitzer and WISE archives. The Herschel observations, using the SPIRE and PACS instruments over a range of 70 m{500 m, were taken as part of the HOBYS Key Programme, and the data were reduced using the HIPE mapmaking environment with sources identified and characterised by the 'get-sources' routine. The Herschel observations cover the peaks of cold dust SEDs, allowing robust estimates of mass and temperature to be made. Comparisons of the Herschel observations of the three regions suggest a picture of star formation in which the densest parts of certain molecular clouds can accrete matter via filaments from the surrounding regions, fuelling far more star formation than occurs in the outer regions. My study of these regions has led to the potential classification of two separate regimes of star formation. The first occurs in filamentary regions (generally observed with a column density of 3 10²¹ cm⁻²-1.5 10²²cm⁻²), and is associated with gravitational accretion. The second occcurs in dense ridges and filamentary hubs (>1.5 10²² cm⁻²), in which intense star formation is fed by material flowing inward, with feedback from newly-formed stars interacting with the infalling material. The identification of these distinct populations is backed up by characterisation of the probability density functions (PDFs) and by determination of local core formation efficiency (CFE), both of which show a regime change at 1.5 10²²cm⁻². Comparisons of source mass, FWHM, and luminosity also indicate a separate population of cores forming in such regions.

No description available.

This thesis contains results on type 1 Active Galactic Nuclei detected and studied with INTEGRAL. The sample of sources analysed in the present thesis is based on a complete sample of type 1 AGN extracted from the 3rd IBIS/ISGRI catalogue. Archival X-ray data taken from several observatories, such as XMM-Newton, Chandra, Swift/XRT and ASCA, have been combined together with IBIS spectra, providing for the first time a broad-band spectral analysis of a hard X-ray detected complete sample of type 1 AGN. The principal aim of this work is to study the continuum properties of type 1 AGN, i.e. power law slope, reflection fraction and high energy cut-off, and their relation to spectral modelling of AGN and to synthesis models of the Cosmic Diffuse X-ray Background. The analysis presented in this work covers two subclasses of type 1 AGN: Broad Line Radio Galaxies (BLRG) and Radio Quiet (RQ) type 1 sources. In particular, among BLRG, IGR J21247+5058 is studied in great depth (see chapter 5). This is in fact a very peculiar source, displaying very complex absorption, in the form of two layers partially covering the central emitting source. So far, only one other BLRG was known to require such complexity regarding absorption (namely 4C 445), making IGR 21247+5058 indeed a very peculiar and almost unique AGN. Broad-band spectra of the other seven BLRG present in the INTEGRAL complete sample have been analysed in search for a dichotomy between this population (chapter 6) and their radio quiet counterparts (chapter 7). Several studies have in fact shown in the past that BLRG might behave differently than radio quiet AGN, displaying weaker reprocessing features (i.e. the reflection component and the strength of the iron line), possibly –i– associated with the presence of the jet. In the present study, however, such diversity is not found to be very striking, with the reprocessing features of the analysed sources not being as weak as expected. This could imply a different scenario for the dilution of these features, not involving a jet but rather a different geometry and/or accretion flow efficiency in the accretion disk. The analysis of the complete sample of type 1 AGN also allows a general picture of the average properties of this class of sources to be obtained. The mean power law slope is found to be Г=1.86±0.01, in good agreement with the generally accepted canonical spectral index of 1.9. The average cut-off energy is Ec=104 keV, lower than previously found in other works; the mean reflection fraction is 1.08±0.14. Correlations between the spectral parameters have also been investigated, but most of them remain still to be proven. When considering these results in the framework of AGN spectral modelling, we found that the average Comptonising plasma temperature is typically ∼50 keV with an optical depth ranging from 2 to 5, i.e. the plasma is not too thick. As far as the Cosmic X-ray Diffuse Background is concerned, synthesis models have so far assumed a spectral shape for the CXB with Г=1.9 with no dispersion in values and a high energy cut-off of at least 200 keV. However, the value of Г=1.86 with a dispersion of 0.2 and a cut-off energy with a narrow range of values around 100 keV, as found in the present thesis, could provide a self-consistent modelling of the CXB. The implementation of the information provided in this thesis is clearly very important for CXB synthesis models and represents the next step of this work.

The main focus of this work is to make use of a novel tool in the cosmologist's toolbox when it comes to constraining the parameters of the peculiar velocity fields of the nearby Universe called ROBUST, whose unique properties and lack of reliance on secondary distance indicators sets it apart from other available constraining techniques, rendering it potentially very useful for future upcoming surveys such as the LSST and the SKA. While ROBUST proves itself more than adequate in constraining parameters in a mock controlled environment with the IRAS PSCz survey, it begins to struggle when applied to the real-world 2MRS survey, primarily due to an inherent fault in the survey that causes it to not function properly with the program. These problems persist even when we begin to make use of one of the ancillary tools developed in conjunction with ROBUST, namely relative entropy, despite it once again continuing to function adequately across multiple mock realisations. It is the conclusion of this work that while ROBUST is not successful in recovering values for the cosmological parameters we seek to constrain, this does not necessarily negate its viability for use with upcoming surveys, as it has proven itself successful in determining exclusion intervals on the value of the linear redshift distortion parameter β for real world surveys that are in very good agreement with the generally small values computed by contemporary velocity-velocity constraining techniques such as VELMOD and χ2 minimisation, while also confidently ruling out the results of older density-density constraining techniques such as POTENT that favour values closer to unity.

Both an experimental investigation of the interaction effects within commercial particulate recording media and a numerical investigation of the reversal mechanism of particles within the media have been made. The particle systems investigated comprised three audio y-Fe203 tapes, three audio Cr02 tapes and a video metal particle tape. An absolute measure of the interaction effects within particulate tapes has been investigated by comparing the measured properties of isolated particles taken from the medium with the measured bulk properties of the medium. The results indicated negative interactions for all the samples investigated except the video metal particle tape, which indicated positive interactions. However, Al plots for all the samples however, indicated negative interactions. This is contrary to the absolute interactions measured in the video metal particle tape. A possible explanation for this inconsistency was the presence of highly localised alignment of particles, "a chaining effect", within the metal particle system. This effect allows for increased system coercivity without removing the general negative interactions characteristic of all acicular particulate media. A micromagnetic model was developed to study typical y-Fe203 and Cr02 particles measured experimentally in this study. Simulations were performed as a function of the applied field angle and the results compared to the experimental study. The simulations representing typical 'y-Fe203 particles indicated reasonable agreement at the lower applied field angles, while poorer agreement was observed at larger applied field angles. The simulations representing a typical Cr02 particle indicated reasonable agreement at the higher applied field angles, while poorer agreement was observed at low applied field angles. These inconsistencies for both types of particles investigated were accounted for by assumptions and simplifications within the model, particularly the absence of bulk crystalline imperfections, the degree of surface irregularities and the effect of an oversimplified particle shape. The micromagnetic model developed was also used to investigate the effect of model parameters on the reversal mechanism of the 'y-Fe203 particle simulation. It was found that the reversal mechanism was very sensitive to the size and shape of the model particle.

A new era of gravitational wave astronomy has begun with the first direct detections of gravitational waves from the collision of binary black holes and a binary neutron star system. The scientific outcomes from these detections have been magnificent, however in order to increase the event rates for known sources, to be sensitive to new sources, to detect sources at greater distances, and to increase the signal to noise ratio for better extraction of source parameters, further research is required to increase the detectors sensitivity. The Advanced LIGO and Advanced Virgo detectors that enabled these first detections will ultimately be limited in their sensitivity by reaching the standard quantum limit (SQL). One novel technique to reduce the influence of quantum radiation pressure noise in a measurement of strain between two test masses is the speed meter topology. As a proof of concept experiment the Glasgow Sagnac Speed Meter experiment aims to show a reduction in quantum radiation pressure noise compared to an equivalent Michelson interferometer at audio-band frequencies. Two triangular cavities are the core of the experiment and consist of two 100g end test masses and one 1g input test masses per cavity, all suspended from multistage pendulums. In this combination the whole Sagnac Speed Meter experiment should be limited by quantum radiation pressure noise from about 100Hz to 1kHz and it is expected to achieve a reduction of quantum radiation pressure noise by a factor of 3-5 compared to an equivalent Michelson interferometer. This thesis presents the development, design, commissioning and testing of the three main types of suspensions in the Sagnac Speed Meter experiment. The longitudinal displacement noise requirement for both cavity suspension types is < 1.5 x 10-18m/√Hz over the measurement band between 100Hz and about 1kHz. In order to isolate the mirrors from seismic ground motion in the Sagnac Speed Meter experiment, they are suspended from multistage pendulums, resulting ideally in a 1/f^2n response for n pendulum stages above the pendulums rigid body modes. Reduction of thermal noise in the suspension elements (suspension thermal noise) is achieved by the introduction of high quality-factor materials in the lowest pendulum stage, making it fully monolithic. The 100g end test mass suspension is based on an existing design, originally developed for the AEI 10m prototype, as a triple suspension with two stages of vertical blade springs and a fully monolithic lowest pendulum stage. The 1g input test mass suspension, designed as a quadruple pendulum with a fully monolithic lowest pendulum stage, utilises the same vertical blade springs and top mass as the 100g end test mass suspension. The quadruple pendulum design enables passive damping of test mass motion at the penultimate stage. As passive damping introduces force noise due to thermal noise, a switchable passive damping system was developed and tested to mitigate limitation by this force noise. The auxiliary suspension, a double pendulum, serves to suspend the mirrors in the experiment that guide the beam towards the Sagnac Speed Meter, in between the cavities, and towards the balanced homodyne detector. As these are not part of the cavities, the longitudinal displacement noise requirement can be relaxed to < 8 x 10-15m/√Hz at 100Hz. The pendulum dynamics of the auxiliary and 100g end test mass suspension were measured in an optical lever set up and, in case of the auxiliary suspension, additionally with a vibrometer. With these measurements, the models were adjusted and could be used to estimate the longitudinal displacement noise due to coupling from seismic ground motion and thus verify the required performance of the suspensions. The research conducted in this thesis is an important step towards establishing the speed meter topology for consideration in future gravitational wave detectors. The developments in the scope of the monolithic assembly for the 100g end test masses will be applied to the AEI 10m prototype in order to enable sub-SQL measurements.

In 2015, a gravitational wave (GW) signal from a binary black hole merger passed through the arms of the US-based Advanced LIGO (aLIGO) interferometers, resulting in the first direct detection of gravitational waves. This long-awaited observation made worldwide news one hundred years after Einstein first predicted the existence of GWs in 1916. Since the first detection, four more binary black hole inspiral events have been detected, as well as the ground-breaking GW observation of a binary neutron star inspiral. To detect these signals, ground-based GW detectors like aLIGO and the French-Italian detector, Advanced Virgo, need to be sensitive to changes in separation of close to 10^-19m between freely suspended test masses spaced up to 4km apart. This has always been a challenge to achieve, thus 50 years of technological developments were needed to make these first detections possible. Following the first observations of coalescing black holes and neutron stars, it is essential to pursue technological advancements that improve the sensitivities of ground-based detectors. Doing so will increase the signal-to-noise ratio of future detectors, which will allow for the better extraction of astrophysical source parameters. Observing more types of astrophysical sources, and at greater distances from the Earth will further the field of GW astronomy. One such area of advancement is to pair the operation of detectors at cryogenic temperatures with improvements in mirror and suspension design, with the aim of improving sensitivities by lessening the effects of thermal noise. Fused silica, currently used for the mirror substrates and suspension fibre elements in all detectors that operate at room temperature, cannot be used in detectors that operate at cryogenic temperatures due to its unfavourable thermo-mechanical properties. Thus a change of mirror substrate and suspension material is necessary for the construction of cryogenic detectors. There are two promising candidates for cryogenic mirrors and suspension elements, sapphire and silicon. Currently one cryogenic detector, the Japan-based KAGRA observatory, is under construction using sapphire as a material for its mirrors and some suspension elements. Other future detectors currently in the design phase, such as the Einstein Telescope (ET) in Europe and Voyager, in the USA may use silicon or sapphire material in their mirror suspensions. In all ground-based detectors the test masses are supported in multi-stage pendulum suspensions, where the last stages are quasi-monolithic. In the quasi-monolithic stage, the test masses are suspended from penultimate masses via fibres, welded to an interface piece, or "ear". Currently these ears are connected to the test masses using a method called hydroxide catalysis bonding, which creates a strong, low noise joint. This bonding technique has been used successfully in room temperature detectors for 17 years. This thesis details research into hydroxide catalysis bonding, with a focus on its use to create cryogenic crystalline suspensions for future ground-based detectors. The use of indium as an alternative bonding technology for joints in low temperature crystalline suspensions is also investigated. The aim of this study is to research possible ways to implement indium bonding into suspension design along with hydroxide catalysis bonds to create a more versatile and easily repairable system. This work was completed with the aim of investigating novel ways of implementing bond techniques into GW detectors, and studying their material properties. The breaking stress and stability of different bond technologies were investigated, as well as their thermal noise levels and impact on overall detector sensitivity. The majority of substrate materials used in this thesis were sapphire and silicon, as these are the two materials of choice for use in future cryogenic detectors. Measurements of the Young's modulus of hydroxide catalysis bonds between fused silica were also completed and used to model the thermal noise contribution of bonds in a prototype test mass for the possible room temperature upgrade to aLIGO, A+. In Chapter 1 an overview of the field of gravitational wave research is given. An explanation of GW sources and a history of the different types of ground-based GW detectors are summarised here, with a focus on Michelson-type interferometric detectors, used to make the first direct GW detections. The noise sources that affect the sensitivity of interferometric detectors are also reviewed. In Chapter 2 there is a summary of several different bonding techniques that could be considered for making joints between the test masses and suspension elements of GW detectors. The mechanisms of bond formation as well as the advantages and disadvantages to each approach are covered, especially in the context of the requirements for use in a GW detector. Finally hydroxide catalysis and indium bonding are introduced as possible techniques to join the suspension and mirror elements in GW detectors. In Chapter 3 the breaking stresses of hydroxide catalysis bonds between c-plane sapphire substrates as a function of time is studied. The aim of this experiment is twofold. The breaking stress of bonds that have been allowed to cure for shorter lengths of time is investigated to gain insight into the chemical processes of the bonds as they develop. Additionally, it is crucial to know the breaking stress over longer periods of curing time to be assured that they will not fail in the long term. In fact, this study found that hydroxide catalysis bonded sapphire shows an initial drop in breaking stress, which then levelled off at 15-16MPa. These results agree with similar trends found in shorter curing time tests on sapphire and fused silica completed in the past. In Chapter 4 the effect of crystal orientation on the tensile strength of hydroxide catalysis bonded sapphire is investigated. Specifically, the breaking stress of bonds between a-a and m-m planes of sapphire jointed with hydroxide catalysis bonds is studied, using samples of the same geometry and jointed using the same bonding procedures as those presented in Chapter 3. These samples were allowed to cure at room temperature for 4 weeks, then the samples were strength tested. The breaking stresses were recorded and compared with the breaking stress results of c-c plane sapphire, also cured for 4 weeks at room temperature, reported in the previous chapter. In Chapter 5 a non-destructive technique of measuring the Young's modulus of hydroxide catalysis bonds between silica and between sapphire is developed. This approach uses acoustic pulses from an ultrasonic transducer transmitted through the bonded samples, and the portion of the acoustic wave that is reflected back from the embedded bond layer is recorded and studied. The bond Young's modulus was extracted from the data by analysis of the amplitudes of the acoustic pulses reflected from the bonds. A Young's modulus value of 15.3+/-5.2GPa for \hcbed sapphire and 21.5+/-6.6GPa for bonded fused silica was found with this approach. A Bayesian analysis model of the reflected acoustic signal and the underlying noise background was developed to analyse the low SNR signals of bonds between fused silica. A value of 18.5+/-2GPa, with a 90% confidence range was found with this approach, agreeing well with the results from the pulse amplitude analysis. In Chapter 6 the new Young's modulus value found in Chapter 5 is used to assess the mechanical loss and thermal noise budgets of hydroxide catalysis bonds in different mirror suspension geometries. Two room temperature test masses were modelled; a bonded aLIGO mass and a bonded prototype test mass, of a design suitable for use in A+. Three different cryogenic masses were also modelled; first a sapphire KAGRA mass, followed by a prototype sapphire ET mass, and a prototype silicon ET mass. / The thermal noise budgets of the bonds in all of these cases were found to be below the anticipated technical noise requirement for bonds, which is based on each detector's current design sensitivity curves. This indicates that hydroxide catalysis bonds are suitable for use in current detectors and for the design of future ones. In Chapter 7 different approaches to creating indium bonding procedures for use in cryogenic ground-based detectors are studied. Hybrid suspension designs that utilize both indium and hydroxide catalysis bonding are being considered in cryogenic detector designs such as KAGRA or ET. It is proposed that the \hydroxide catalysis bonds would be used to fix the test masses to the suspension elements. This takes advantage of their high breaking stress under shear and peeling, as has been successfully demonstrated in the past for room temperature detectors such as Virgo, aLIGO, or the Germany-based detector GEO600. Indium's low tensile strength means it cannot be used as a joint under tensile or shear load. However it is being considered for use in compressive joints, such as between the fibres and ears or between the fibres and blade springs. This would be done for contingency reasons, since indium can be de-bonded and re-bonded relatively easily, whereas hydroxide catalysis bonds cannot. In the event of a fibre break or a test mass upgrade, the whole bonded test mass assembly could be removed by de-bonding the indium bond interface. It could then be replaced by re-bonding it, making it a good option for future cryogenic mirror suspensions. Two indium bonding approaches are investigated, diffusion bonding and induction bonding. In both cases the substrates used were polished silicon, and the indium layers between them were made with different combinations of thin thermally deposited films and foils. The tensile strength and a post-break visual inspection of the indium bonds were used as a standard by which to judge bond quality and repeatability.

Gravitational waves are considered as ripples in the curvature of space-time and were predicted by Einstein in his general theory of relativity. Gravitational waves interact very weakly with matter which makes them very difficult to detect. However, research groups around the world are engaged in building a network of ultra sensitive ground and space based interferometers for the first detection of these signals. Their detection will open a new window in the field of astronomy and astrophysics. The nature of gravitational waves is such that when incident on a particle, they stretch and squeeze the particle orthogonally thus producing a tidal strain. The strain amplitude expected for gravitational waves which may be detected on earth are of the order of hrms ~10-22 to 10-23 (over a frequency range from few Hz to a few kHz). A network of instruments based on the Michelson interferometer design currently exists around the world. These detectors are undergoing a major upgrade and once online by 2015-16 the improved sensitivity and increased sky coverage may lead to the first detection of the gravitational waves signals. The Institute for Gravitational Research in the University of Glasgow in collaboration with the Albert Einstein Institute in Hannover, Golm and the University of Cardiff has been actively involved in the research for the development of instruments and data analysis techniques to detect gravitational waves. This includes construction of a long ground based interferometer in Germany called GEO 600 (upgraded to GEO-HF) having an arm length 600 m and strong involvement in the larger detectors of the LIGO (Laser interferometer gravitational wave observatory) project in USA having arm lengths of 4 km (Operated by MIT, Boston and CALTECH, Pasadena). An upgrade to LIGO called Advanced LIGO (aLIGO) is currently under construction with significant input from the University of Glasgow. Thermal noise is one of the most significant noise sources affecting the sensitivity of the detector at a range of frequencies. Thermal noise arises due to the random fluctuations of atoms and molecules in the materials of the test mass mirrors and suspension elements, and is related to mechanical loss in these materials. The work presented in chapter 3 of this thesis is devoted to the analysis of aspects of mechanical loss and thermal noise in the final stages of the GEO suspension. GEO-600 is currently undergoing an upgrade to GEO-HF targeting sensitivity improvements in the kiloHertz region. However, the planned upgrade requires access to the vacuum tanks enclosing the fused silica suspension system. There is a risk of damaging the suspension, which has led to a repair scenario being developed in Glasgow, to reduce the downtime of the detector. An optimised design of the fused silica fibre has been proposed. A study of mechanical loss has been undertaken through Finite Element Analysis (FEA) modeling techniques. The mechanical loss of the optimised fibre is estimated to be lower than the original GEO fibre by a factor of ~4. In terms of thermal noise performance the optimised fibre gives an improvement of ~1.8. The repair scenario of the monolithic suspension has led to the development of tools and welding procedures. Three prototype suspensions involving metal masses were successfully built, before fabricating the monolithic fused silica suspension in Glasgow. The work in chapter 4 focuses on the theory of photoelasticty and birefringence techniques. The production and use of various forms of polarised light has been discussed. A setup of plane and a circular polariscope using two polarisers and two-quarter wave plates has been shown. The retardation of light due to the birefringence in the sample can be measured using the Tardy method of compensation and a Babinet-Soleil compensator. Finally a discussion on the stress-optic law has shown that the relative stress in a sample can be measured once the retardance is known. The silica fibres in the aLIGO detector would be laser welded using a 100 W CO2 laser. The laser welding would lead to high temperature and development of thermal gradients. This could result in residual thermal stress in fused silica, which could lead to an additional mechanical loss. A study of mechanical and thermal stress induced in fused silica has been discussed in chapter 5 of this thesis. To understand the working of photoelastic techniques learned in chapter 4, a study of mechanical stress was undertaken by applying a load on the sample to induce temporary birefringence. The estimated values of stress showed a good agreement when compared with the theoretical predictions and FEA modelling. Thermal stress was induced in fused silica by applying a 25 W CO2 laser beam for 10 seconds and the relative stress was measured using photoelastic birefringence techniques. Thermal modelling of the stressed sample was performed using the techniques developed in FEA. The experimental values show a good agreement with the estimated 1st principal stress (FEA model) and equivalent stress. A study of thermal stress in fused silica welds has also been presented in chapter 5. Two fused silica samples were welded using CO2 laser welding and the relative stress at different points were measured. The stress in the weld region was measured to be relatively lower than other areas. At a distance of 3 mm away from the weld line the maximum stress was measured which was greater than the stress in the weld region by a factor of ~5. The work discussed in chapter 6 focuses on the study of the suspension thermal noise in aLIGO detector for applying incremental upgrades. To further enhance the sensitivity of the aLIGO detector, incremental upgrades could be applied to the suspension system to improve the thermal noise. The incremental upgrades focused on two aspects: improving the dissipation dilution factor, and obtaining a lower mechanical loss than the aLIGO baseline. Based on the results from FEA, two designs were compared, each having a suspension of length 100 cm but different stock diameter - 3mm and 5 mm. A comparison with the aLIGO baseline showed that these two models obtained a lower mechanical loss by a factor of 3.4 to 6.8. In terms of suspension thermal noise there was an improvement by factor of 2.5 to 3.7, which could lead to rise in the sensitivity of the detector by a factor of 2.5.

Central massive objects like supermassive black holes and stellar nuclear clusters are common in all type of galaxies. I use N-body simulations to study the formation and evolution of nuclear clusters and to investigate the influence of the dynamical evolution of disc galaxies on the structural and kinematical properties of the host galaxy. I show that the second moment of velocities determine a lower limit on the dissipative formation process, which is about 50% in the case of the nuclear cluster in the late-type spiral galaxy NGC 4244. The vertical anisotropy of nuclear clusters can be used to determine an upper limit on the formation process due to merger or accretion of star clusters, which is about 10% for the nuclear cluster in NGC 4244. This is the first time that we have strong evidence of a hybrid formation scenario for nuclear clusters. In a set of 25 galaxy simulations I study bar formation in disc galaxies. I show that bar formation lead to the increase in mass in the central region of galaxies. This mass increase raises the velocity dispersion of stars in the disc and bulge component, which explains the offset of barred galaxies in the relation between the mass of the supermassive black hole, Ml, and the velocity dispersion of stars in the bulge, se , the Ml - se relation (Gueltekin et al. 2009). While Graham et al. (2011) argued that the orbital structure of stars within the bar could be responsible for the observed offset of barred galaxies from the Ml - se relation of unbarred galaxies, I show that the effect of stellar orbits in bars on se is less than 15% compared to the increase in mass which raises se by 40%. The offset I find in the simulation is comparable to the offset using the recent sample of Ml measurements of elliptical, unbarred and barred disc galaxies from Gueltekin et al. (2009).

The chemistry of galaxies provides a powerful probe of the underlying physics driving their evolution, complementing the traditional tools of morphology, kinematics,and colours. This dissertation examines several aspects of the galactic chemical evolution of late-type galaxies - both disc-like and dwarf - using a suite of cosmological hydrodynamical simulations, which incorporate the nucleosynthetic pollution of the interstellar medium, supplemented with classical analytical models of Local Group dwarfs. Throughout the work, these models are confronted with extant observations of both local and high-redshift systems, in order to identify both the strengths and weaknesses of the current generation of galaxy models. The work here has been presented across four primary science chapters which follow on from the Introduction and Motivation, prior to closing with the Conclusions and Future Directions. The first science result (Chapter 2) derives from an examination of the cold (neutral)gas content of the first-ever simulated bulgeless dwarf disc galaxies (Governato et al. 2010), and builds upon the work first presented in Pilkington et al. (2011). The focus of the work is on comparing the observables inferred from the simulated interstellar media, with those seen in nature (including The HI Nearby Galaxies Survey and the Magellanic Clouds), including their velocity dispersion profiles, disc flaring, and the distribution of power within the ISM’s structure, on different scales. Going beyond the work in Pilkington et al. (2011), two additional simulations from the Governato et al. (2010) suite are included, and the original work has been extended to include an analysis of the chemical properties of the dwarf galaxies. The second science result (Chapter 3) examines the role of feedback, metal diffusion, and initial mass function selection, on the resulting chemistry of a new grid of M33-like disc simulations. The emphasis of the analysis is upon the resulting age-metallicity relations and metallicity distribution functions (in particular, the extreme metal-poor tail). Aspects of the work have been presented by Pilkington et al. (2012b), enhanced here by a further examination of the satellites associated with their respective host galaxies. The satellites are seen to be free of gas, with star formation histories which make them not unlike Local Group dwarf spheroidals. The third science result (Chapter 4) is based upon an analysis of the temporal evolution of metallicity gradients in Milky Way-like systems, and derives from the work presented in Pilkington et al. (2012d). A large suite of simulations, sampling a range of numerical codes (particle- and grid-based, in addition to classical Galactic Chemical Evolution (GCE) models), each with different treatments of star formation, energy feedback, and assembly histories, was employed. The analysis focussed on both the radial and vertical abundance gradients, emphasising the role of feedback in shaping the gradients, and demonstrates the critical role that new observations of in situ gradients at high-redshift can play in constraining the uncertain nature of feedback within simulations. This work has been complemented by a brief examination of the azimuthal abundance variations in the massive discs. The fourth science result (Chapter 5) expands upon our earlier exploration of the chemical properties of simulated dwarf galaxies, but now employs a classical semi-numerical GCE approach. By coupling colour-magnitude diagram-constrained star formation histories with our GEtool GCE code, we attempt to constrain the relative rates of gas infall and outflow, for the Carina, Fornax, and Sculptor Local Group dwarfs, in order to match their empirical chemical abundance patterns and metallicity distribution functions. This builds upon the preliminary work, as presented by Pilkington & Gibson (2012a).