Upon its completion the Herschel ATLAS (H-ATLAS) will be the largest submillimetre survey to date, detecting close to half-a-million sources. It will only be possible to measure spectroscopic redshifts for a small fraction of these sources. However, if the rest-frame spectral energy distribution (SED) of a typical H-ATLAS source is known, this SED and the observed Herschel fluxes can be used to estimate the redshifts of the H-ATLAS sources without spectroscopic redshifts. In this thesis, I use a subset of 40 H-ATLAS sources with previously measured redshifts in the range 0.5 < z < 4.2 to derive a suitable average template for high redshift H-ATLAS sources. I find that a template with two dust components (Tc = 23.9 K, Th = 46.9 K and ratio of mass of cold dust to mass of warm dust of 30.1) provides a good fit to the rest-frame fluxes of the sources in our calibration sample. I use a jackknife technique to estimate the accuracy of the redshifts estimated with this template, finding a root mean square of ∆z/(1 + z) = 0.26. For sources for which there is prior information that they lie at z > 1 we estimate that the rms of ∆z/(1 + z) = 0.12. I have used this template to estimate the redshift distribution for the sources detected in the H-ATLAS equatorial fields, finding a bimodal distribution with a mean redshift of 1.2, 1.9 and 2.5 for 250, 350 and 500 µm selected sources respectively. Using these redshifts I have estimated luminosity functions for the Phase 1 field. This has shown evidence of strong evolution out to a redshift of z ∼ 2. At which point luminosity evolution begins to slow until z ∼ 3, where it appears to stop altogether. Estimations of the angular correlation function showed strong clustering across most wavelengths and redshifts.

This thesis is broadly concerned with the dynamics, statistics and phenomenology of the perturbed Universe. By studying the perturbations to cosmological spacetimes, and the subsequent growth of large scale structure, we find that we can link both fundamentally and astrophysically interesting physics to cosmological observables. We use a healthy mix of statistical, analytical and numerical techniques throughout this thesis. In Chapter 2 we introduce and summarise the statistics of random fields, as these are fundamental objects used to model cosmological observables. We introduce the spherical Fourier-Bessel expansion as a tool to perform genuine 3-dimensional studies of cosmological random fields. In Chapter 3 we introduce the theory of inflation and discuss the basic machinery that allows us to calculate the statistical properties of the quantum mechanical flucatuations that seed large scale structure. What we see is that different fundamental physics in the early Universe leads to different statistical properties that we may test. The second half of Chapter 3 introduces the large scale structure of the Universe that describes the clustering of galaxies on cosmological scales. We discuss the growth and evolution of structure under gravitational collapse and the core observables that are predicted, such as the power spectrum, variance and skewness. Chapter 4 introduces the Minkowski functionals. These are a set of topological statistics that probe the morphological properties of random fields. In particular they may be used to quantify deviations from Gaussianity in the large scale structure of galaxies. The deviations from Gaussianity can be generated by two primary mechanisms: 1) The gravitational collapse of perturbations is a non-linear process. Even if we have Gaussian initial conditions, gravitational collapse will induce non-Gaussianity. 2) Different theories for the early Universe will imprint different non- Gaussian features in the primordial perturbations that seed large scale structure, i.e. we have non-Gaussian initial conditions. We can connect the amplitude and momentum dependence of the non-Gaussianity to different fundamental interactions. We introduce a topological statistic based on the Minkowski functionals that retains the momentum dependence giving us greater distinguishing power between different contributions to non-Gaussianity. In Chapter 5 we introduce the Baryon Acoustic Oscillations (BAOs) as described in the spherical Fourier-Bessel formalism. The BAOs are a solid prediction in cosmology and should help us to constrain cosmological parameters. We implement a full 3-dimensional study and study how redshift space distortions, induced by the motion of galaxies, and non-linearities, induced by gravitational collapse, impact the characteristics of these BAOs. Chapter 6 extends the spherical Fourier-Bessel theme by introducing the thermal Sunyaev- Zel’dovich (tSZ) effect and cosmological weak lensing (WL). It is thought that weak lensing will provide an unbiased probe of the dark Universe and that the tSZ effect will probe the thermal history of the Universe. Unfortunately, the tSZ effect loses redshift information as it is a line of sight projection. We study the cross-correlation of the tSZ effect with WL in order to reconstruct the tSZ effect in a full 3-dimensional study in an attmept to recover the lost distance information. We use the halo model, spectroscopic redshift surveys and suvery effects to understand how detailed modelling effects the tSZ-WL cross correlation. Chapter 7 marks a real change in theme and introduces the subject of relativistic cosmology. Inparticular we introduce the 1+3, 1+1+2 and 2+2 formalisms as tools to study cosmological perturbations. We provide rather self-contained introductions and provide some minor corrections to the literature in the 1+1+2 formalism as well as introducing new results. In Chapter 8 we apply the 1+1+2 and 2+2 approaches to the Schwarzschild spacetime. Here we outline the full system of equations in both approaches and how they are related, setting up a correspondence between the two. Our aim is to construct closed, covariant, gauge-invariant and frame-invariant wave equations that govern the gravitational perturbations of the Schwarzschild spacetime. We correct a result in the literature and derive two new equations. The first governs axial gravitational perturbations and is related to the magnetic Weyl scalar. The second is valid for both polar and axial perturbations and is given by a combination of the magnetic and electric Weyl 2-tensors. We discuss their relation to the literature at large. Finally, in Chapter 9 we apply the 1+1+2 and 2+2 approaches the LTB spacetime. This inhomogeneous but spherically symmetric spacetime is the first stepping stone into genuinely inhomogeneous cosmological spacetimes. We seek a closed, covariant master equation for the gravitational perturbations of the LTB spacetime. We present an equation governing axial gravitational perturbations and a preliminary equation, valid for both the polar and axial sectors, that is constructed from the electric and magneticWeyl 2-tensors but is coupled to the energy-momentum content of the LTB spacetime. We discuss how auxilliary equations may be introduced in order to close the master equation for polar and axial perturbations. This last result leads to the identification of H as a master variable for axial perturbations of all vacuum LRS-II spacetimes and the LTB spacetime. It is thought that these results can be extended to non-vacuum LRS-II spacetimes. Likewise, the master variable constructed from Weyl variables constitutes a master variable for all vacuum LRS-II spacetimes and it is thought that this will extend to the non-vacuum case.

The detection of dark matter (DM) by direct detection experiments has great potential to shed light on particle physics beyond the Standard Model. However, uncertainties in the DM speed distribution f1(v) may lead to biased reconstructions of particle physics parameters, such as the DM mass and interaction cross sections. In this work, we aim to determine whether these parameters can be determined from future direct detection data without any prior assumptions about f1(v). We study previous methods for parametrising f1(v) and show that they may still lead to biased reconstructions of the DM parameters. We propose an alternative smooth, general parametrisation, which involves writing the logarithm of the speed distribution as a polynomial in v. We test this method using future direct detection mock data sets and show that it allows an unbiased reconstruction of the DM mass over a range of particle physics and astrophysics parameters. However, the unknown fraction of DM particles with speeds below the energy thresholds of the experiments means that only a lower bound can be placed on the interaction cross sections. By introducing data from neutrino telescope experiments, such as IceCube, this degeneracy in the cross section can be broken, as these experiments probe the low speed DM population. Combined with our parametrisation method, this allows a robust reconstruction of the DM mass and cross sections without relying on any assumptions about the DM speed distribution. The function f1(v) itself can also be reconstructed, allowing us to probe the distribution function of the Milky Way. Finally, we propose a method of extending this parametrisation to directional data, which should allow even more information to be extracted from future experiments without the need for astrophysical assumptions.

The properties of galaxy clusters, such as abundance and mass to light ratios, have long been used to investigate and constrain cosmology. With vast numbers of newly detected clusters, such as from the Planck mission (Planck Collaboration et al., 2013), full determination of cluster properties, particularly mass, can be hugely expensive and time consuming. Optical characterisation o ers a cheap solution, using optical data alone to estimate cluster properties such as redshift. With the abundance of current optical data, such as from the Sloan Digital Sky Survey (SDSS), (Ahn et al., 2012) and upcoming all sky surveys, such as the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) 3 survey (Magnier et al., 2013), optical characterisation will play a key role in the investigation of the latest clusters. Presented in this thesis is the Gaussian Mixture full Photometric Red sequence Cluster Characteriser (GMPhoRCC), which aims to provide such an analysis, o ering substantial advantages over existing algorithms. GMPhoRCC identi es and models the red sequence, early-type galaxies which dominate the cluster, and uses the properties of this to estimate cluster redshift and richness, an optical mass proxy based on the number of cluster members. The main features include, full treatment of multi-modal distributions by modelling properties with error-corrected Gaussian Mixtures, model independence by using empirical photometric redshifts rather than assumed colour-redshift relations and quality control used to identify probable catastrophic failures in order to clean the characterisations. Using a sample of 5500 clusters taken from the GMBCG (Hao et al., 2010), NORAS (Bohringer et al., 2000), REFLEX (Bohringer et al., 2004) and XCS (Mehrtens et al., 2012) catalogues, GMPhoRCC redshift estimates are compared to spectra showing low scatter ( σ∆z~ 0:042) around the actual value. In addition applying the quality control to produce a clean subset removes most outliers (|zGMPhoRCC-zspec| > 0:03) gives a much tighter agreement, σ∆z~ 0:018 showing signi cant improvement over maxBCG, σ∆z~ 0:025, and XCS, σ∆z~ 0:050. In addition to comparisons with real clusters, an extensive evaluation of the GMPhoRCC selection function is presented using mock clusters. These mocks are produced by stacking red sequence galaxies from existing clusters, analysed using the SDSS DR9, in redshift-richness bins from which new sequences are resampled. This extends the similar approach of maxBCG and GMBCG where only rich clusters are used as seeds to generate mocks with a range of properties. Comparisons with mocks agree well with real clusters attaining low redshift scatters ( σ∆z~ 0:01) with the clean subset removing the majority of outliers. In addition, with a de nitive mock value, richness comparisons are possible and although show a larger fractional scatter (σ∆z n200 ~ 0:12) are centred on the mock value. Richness estimates are shown to be more sensitive to discrepancies in redshift, background uctuations and poor modelling of the red sequence than redshift. Completeness is estimated by considering the fraction of clusters found with characterisations within given bounds. First incomplete photometry, simulated by an i-band < 21 cut, is shown to remove members for clusters with z > 0:45. Redshift completeness, the fraction of clusters within 0:03 of the mock value, is not immediately hindered by the photometry, attaining 93% for 0:05 < z < 0:62 for clusters with a richness greater than 20, showing improvement over maxBCG (with 90% for 0:1 < z < 0:3) and a larger range than GMBCG (with 96% for 0:1 < z < 0:46). Similar to results from GMBCG, richness attains lower completeness rates due to discrepancies introduced by projection e ects, background uctuations, and redshift errors. The fraction of clusters within 25% of the mock value, de ning completeness, is measured as 91% for 0:07 < z < 0:45 for clusters with richness greater than 20, 78% for those with richness between 10 and 20, and 64% for those with richnesses less than 10. The application of GMPhoRCC follows, where characterisations are found for new XCS X-ray extended sources (Lloyd-Davies et al., 2011). Applying GMPhoRCC to these preliminary DR2 candidates ( 10 times larger than the current catalogue) using the VLT Survey Telescope (VST) ATLAS catalogue (Shanks & Metcalfe, 2012) and the much deeper Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) (Heymans et al., 2012) provides characterisations beyond the SDSS footprint. Of the 13; 956 candidates, 6124 have optical coverage, 5580 in the SDSS, 523 in ATLAS and 819 in CFHTLenS with some overlap. Overall characterisations are found for 4365 candidates, 1893 of which have an associated spectroscopic redshift. The clean subset comprises 1203 candidates, 904 with spectra. Considering XCS DR1, Mehrtens et al. (2012) presented 503 optically con rmed X-ray clusters of which 258 have spectroscopic redshifts and 108 have SDSS characterisations. GMPhoRCC provides characterisations for 360, 232 of which have spectroscopic redshifts. Overall GMPhoRCC provides 260 (149 of which are clean) new SDSS characterisations and 91 (61 of which are clean) new spectroscopic redshifts. Finally this thesis concludes with a discussion of future research, focusing mainly on a preliminary analysis of a clean spectroscopic subset of XCS DR1 in order to illustrate the potential to constrain X-ray scaling relations with the upcoming XCS DR2. Additionally, potential research into the e ect of environment on the red sequence is illustrated using the dependence of the CMR slope on X-ray temperature. While a slight dependence is found, the cluster sample is insu cient to contradict the independence on environment found by Hogg et al. (2004) and Hao et al. (2009).

This thesis explores the evolution of massive galaxies (M * > 1011M ʘ) by conducting the largest multiple-component Sersic light-profile fitting study to date of the rest-frame optical and ultra-violet morphologies of galaxies at redshifts 1 < z < 3. Despite many of the recent advances in galaxy formation and evolution models, the physical processes which are responsible for driving morphological transformations and star-formation quenching remain unclear. By undertaking a detailed study of the individual bulge and disk components of these massive systems, the work presented in this thesis addresses these outstanding issues by exploring not only how the sizes of the individual components evolve with redshift, but also how the overall bulge and disk fractions evolve, and how these trends are connected to star-formation quenching of the separate components. In order to perform this analysis, I have combined the latest high-resolution near-infrared HST WFC3/IR and ACS imaging provided by the CANDELS survey in the UDS and COSMOS fields and have presented a robust procedure for morphological multiple-component Sersic light-pro le model fitting across the 0:6μ m to 1:6μ m wavelength range sampled by CANDELS. This procedure is discussed in depth along with the tests I have undertaken to assess its reliability and accuracy. This approach has enabled me to generate separate bulge and disk component model photometry, allowing me to conduct individual component SED fitting in order to determine decomposed stellar-mass and star-formation rate estimates for the separate bulge and disk components. The results presented in this work reveal that the sizes of the bulge and disk components lie both on and below the local size-mass relations, confirming that the size evolution required by the previously reported compact sizes of high-redshift galaxies extends to both galaxy components. However, I find evidence that the bulge components display a stronger size evolution with redshift than the disks as, at 1 < z < 3, the bulges are a median factor of 3:09 ± 0:2 times smaller than similarly massive local early-type galaxies, whereas the disks are a median factor of 1:77 ± 0:1 times smaller than similarly massive local late-type galaxies. By including decomposed star-formation rates for the individual bulge and disk components, this work also reveals that while the growth of individual components through, for example, inside-out processes such as minor merging, are consistent with the size evolution of these systems, the addition of larger newly quenched systems to the galaxy population, for the disk components at least, may also play an important role in the observed size evolution of massive galaxies. By exploring the evolution of the bulge and disk-dominated fractions with redshift, I find that 1 < z < 3 marks a key transition era in cosmic time where these most massive galaxies appear to be undergoing dramatic structural transformations. Within this redshift range there is a decline in the population of disk-dominated galaxies and a gradual emergence of increasingly bulge-dominated systems. However, despite the rise of S0-type galaxies, even by z = 1 I do not yet find a significant fraction of "pure" bulges comparable to the giant ellipticals which comprise the majority of the local massive galaxy population. In addition to studying how the overall bulge and disk dominated fractions evolve with redshift, by incorporating the star-formation rate and stellar-mass estimates for the separate components and imposing new, highly conservative criteria, I con firm that a significant fraction of passive galaxies are disk-dominated (18± 5%) and a significant fraction of star-forming galaxies are bulge-dominated (11 ±4%). The presence of passive disks and star-forming bulges has interesting implications for the models of galaxy evolution as they suggest that the processes which quench star-formation may be distinct from the mechanisms which cause morphological transformations. Finally, the detailed morphological analysis presented in this work has also allowed me to explore the axial ratio distributions of these most massive high-redshift galaxies, which provides additional insight into the structure of the passive and star-forming bulge and disk-dominated sub-populations. Whilst the overall axial ratio distributions for star-forming disks are peaked, I find tentative evidence that the largest and most active star-forming disks are flatter. I have also been able to further demonstrate that by selecting the most active star-forming disks and comparing to extreme star-forming (sub-)mm selected galaxies, the axial ratio distributions of the two samples appear to be comparably flat, thus reconciling the observed structures of these populations.

Lenticular (S0) galaxies have long been thought of as evolved spirals, in which the star formation has been suppressed, the spiral arms have faded, and the luminosity of the bulge has been built up relative to the disc. However, the sequence of events that explains these three observations and leads to the formation of the final S0 galaxy is still uncertain. The progenitor spirals generally consist of bulges with old stellar populations surrounded by young, bright discs. Therefore, in order to explain the `quenching' of star formation in the disc and related increase in the bulge luminosity, an understanding of the individual star-formation histories of these two components is vital. In this thesis, we present a new technique to spectroscopically decompose the light from a galaxy into its bulge and disc components, from which the stellar populations and chemical compositions of the individual components can be extracted in order to determine the sequence of events leading to the transformation. Using spectroscopic bulge-disc decomposition, the spatial light profile in a two-dimensional galaxy spectrum can be separated wavelength-by-wavelength into bulge and disc components. This decomposition allows the construction of separate one-dimensional spectra representing purely the light from the bulge and disc, enabling studies of their individual star-formation histories with minimal contamination. This technique was applied to a sample of 30 S0s in the Virgo and Fornax Clusters, and analysis of the absorption line strengths within these spectra reveals that the bulges contain consistently younger and more metal-rich stellar populations than their surrounding discs. This result implies that the final episode of star formation before the progenitor spirals were fully quenched occurred in their central regions. Furthermore, the similarity in the alpha-element abundances of the bulges and discs indicates that the final episode of star formation in the bulge was fuelled using gas that has previously been chemically enriched in the disc. Together, these results present a picture in which the galaxy starts out as a typical spiral, with an old bulge surrounded by a young, star-forming disc. At some point in its life, gas is stripped from the galaxy, suppressing the star formation in the disc and causing the spiral arms to fade without inducing significant amounts of new star formation or disrupting the overall morphology of the galaxy. As the gas is removed, a fraction is also driven into the centre of the galaxy, where it fuels a final star-formation event in the bulge. This final episode of star formation consequently increases the luminosity of the bulge as the disc is already fading, and produces a central young, metal-rich stellar population. We have also shown that it is possible to spectroscopically decompose a galaxy using the different line-of-sight velocity distributions of kinematically distinct components. This technique was applied to NGC~4550, an unusual S0 galaxy in the Virgo Cluster with two counter-rotating stellar discs and a gaseous disc, to separate their individual stellar populations. Analysis of these stellar populations shows that the disc that co-rotates with the ionized gas is brighter and has a significantly younger mean age than the other disc, which are consistent with more recent star formation fuelled by the associated gaseous material. Therefore, the most likely formation mechanism for this galaxy is via an unusual gas accretion or merger scenario that built up a secondary stellar disc in a pre-existing S0 galaxy. The results presented in this thesis shed new light on the sequence of events that leads to the formation of S0 galaxies in cluster environments, and clearly demonstrates the importance of understanding the star-formation histories of the individual components within these galaxies in order to reconstruct the range of mechanisms by which they formed.

USING multiwavelength observations, centred around the unique far-infrared and submillimetre window provided by the Herschel Space Observatory, this thesis investigates the origins and evolution of cosmic dust in the local Universe – by examining individual sources of dust in our own galaxy, and by studying dust in nearby galaxies. Herschel observations of the remnants of Kepler’s (SN1604) and Tycho’s (SN1572) supernovae, both Type-Ia explosions, are searched for evidence of dust creation by these events. Being the only Type-Ia supernovae known to have occurred in our Galaxy within the past 1,000 years, these remnants are the only ones both close enough to resolve, and young enough that they are dominated by their ejecta dynamics. There is no indication of any recently manufactured dust associated with either supernova remnant. It therefore appears that Type-Ia supernovae do not contribute significantly to the dust budgets of galaxies. The Crab Nebula, the result of a Type-II supernova (SN1054), is also investigated using Herschel and multiwavelength data. After accounting for other sources of emission, a temperature of Td = 63.1K and mass of Md = 0.21M⊙ is derived for the Crab Nebula’s dust component. A map of the distribution of dust in the Crab Nebula, the first of its kind, is created by means of a resolved component separation, revealing that the dust is located in the dense filamentary ejecta. We can be confident that this dust will survive in the long term, and be injected into the galactic dust budget. This is the first detection of manufactured supernova dust for which this can be said. I next use the Herschel-ATLAS to assemble HAPLESS: the Herschel-ATLAS Phase-1 Limited Extent Spatial Sample – a blind, volume-limited, dust-selected sample of nearby galaxies. The majority of this sample is made up of curious very blue UV-NIR colours, these galaxies appear to be prominent in the local dusty universe. In the absence of reliable photometry for the HAPLESS galaxies, I describe the function and testing of a purpose-built photometric pipeline – CAAPR: Chris’ Adequate Aperture Photometry Routine. The photometry conducted with CAAPR exhibits flux greater by factors of, on average, 1.6 in the FUV and 1.4 in r-band, relative to the previously-available photometry.

Active galactic nuclei (AGN) are some of the most energetic objects which have ever been observed and each of these harbour a supermassive black hole at its centre. By looking at the X-ray emission from these nuclei, information can be gathered regarding their inner workings. Emission from regions which are very close to the central black hole can be subject to strong relativistic effects and the examination of this emission can lead to the placing of estimates upon the rate at which the black hole is spinning. Within this thesis, I make an analysis of all Seyfert 1 observations which have been observed with Suzaku to date, although using selection criteria such that broad features in the FeK region can be observed if they are indeed present. Models are constructed of the time-averaged broadband spectra over 0.6-60.0 keV, which accurately describe these complex AGN and allow the measurement of the impact relativistic effects have upon the X-ray spectrum. There are a total of 46 different objects and 84 observations used within this analysis. By conducting a full broadband analysis of these AGN, supermassive black hole spin constraints are placed upon 11 objects, 7 of which are unique to this analysis with the remaining 4 either confirming or improving upon previous analyses. In general, it is found that 50% of the objects in this sample show evidence for emission from the inner regions of the nucleus although none of the AGN require a maximally spinning black hole, which is in contrast to the results in alternative analyses. The data within this thesis are best described with emission originating from no further in than a few tens of Rg.

Inflation is an early period of accelerated cosmic expansion, thought to be sourced by high energy physics. A key task today is to use the influx of increasingly precise observational data to constrain the plethora of inflationary models suggested by fundamental theories of interactions. This requires a robust theoretical framework for quantifying the predictions of such models; helping to develop such a framework is the aim of this thesis. We begin by providing the first complete quantization of subhorizon perturbations for the well-motivated class of multi-field inflationary models that possess a non-trivial field metric. In particular, the implications for the bispectrum of the Cosmic Microwave Background (cmb) are potentially very exciting. The subsequent evolution of perturbations in the superhorizon epoch is then considered, via a covariant extension of the transport formalism. We demonstrate appropriate matching between the subhorizon and superhorizon calculations. With the aim of developing intuition about the relation between inflationary dynamics and the evolution of cosmic observables, we investigate analytic approximations of superhorizon perturbation evolution. The validity of these analytic results is contingent on reaching a state of adiabaticity which we discuss and illustrate in depth. We then apply our analytic methods to elucidate the types of inflationary dynamics that lead to an enhanced cmb non-Gaussianity, both in its bispectrum and trispectrum. In addition to deriving a number of new simple relations between the non-Gaussianity parameters, we explain dynamically how and why different shapes of inflationary potential lead to particular observational signals. In addition to multiple scalar fields, candidate theories of high energy physics include many possible modifications to the Einstein{Hilbert action. We consider the observational viability of single field chaotic inflation with additional corrections as motivated by low energy effective string theory. These new ingredients allow for consistency of chaotic inflationary models that are otherwise in tension with observational data.

Much of the evolution of galaxies takes place in groups where feedback has the greatest impact on galaxy formation. By using an optically selected, statistically complete sample of 53 nearby groups (CLoGS), observed at radio (GMRT) and X-ray (Chandra and XMM-Newton) frequencies, we aim to characterise the radio-AGN population in groups and examine their impact on the intra-group gas and member galaxies. In this dissertation, low-frequency GMRT radio images of the nearby (<80 Mpc) central brightest group ellipticals from the high richness CLoGS sub-sample are presented for the first time at 235 and 610 MHz. Using the sensitivity to older electron populations at 235 MHz and the resolution of 610 MHz as a key to identify past and current AGN activity, a detailed analysis of the radio properties for each of the central group radio sources is performed, with the results being in addition combined with findings from the X-ray observations.