This thesis is concerned with the interface of cosmology and condensed matter. Although at either end of the scale spectrum, the two disciplines have more in common than one might think. Condensed matter theorists and high-energy field theorists study, usually independently, phenomena embedded in the structure of a quantum field theory. It would appear at first glance that these phenomena are disjoint, and this has often led to the two fields developing their own procedures and strategies, and adopting their own nomenclature. We will look at some concepts that have helped bridge the gap between the two subjects, enabling progress in both, before incorporating condensed matter techniques to our own cosmological model. By considering ideas from cosmological high-energy field theory, we then critically examine other models of astrophysical condensed matter phenomena. In Chapter 1, we introduce the current cosmological paradigm, and present a somewhat historical overview of the interplay between cosmology and condensed matter. Many concepts are introduced here that later chapters will follow up on, and we give some examples in which condensed matter physics has had a very real effect on informing cosmology. We also reflect on the most recent incarnations of the condensed matter / cosmology interplay, and the future of these developments. Chapter 2 presents the Einstein-Klein-Gordon system of equations and their non-relativistic and nonlinear counterparts, the Schrodinger-Poisson, and nonlinear Schrodinger (Gross Pitaevskii)-Poisson systems. We give a more technical overview of the various applications of these systems of equations, as well as discussing the role and interpretation of condensates in the field of cosmology. In Chapter 3 we discuss more qualitatively the fluid-mechanical methods used in a wave-mechanical approach to structure formation, and in formulations of condensed matter models. Taking a lead from the condensed matter side, we look at some of the details of the Gross-Pitaevskii equation, particularly with regard to quantum vortices, and then put this quantum-mechanical system into a cosmological environment by coupling it to the Poisson equation, in an effort to pin down some of the parameters that may be consistent with the existence of vortices in a cosmological Bose-Einstein condensate. In Chapter 4 we turn to high-energy field theory and elucidate further some of the relationships with condensed matter physics that are present. We also critically examine a Bose-Einstein dark matter model in light of these considerations. Chapter 5 rounds off with a discussion and suggestions for further work based upon models we have discussed, as well as some ideas for models that have not yet been mentioned. An appendix discusses techniques for moving from the relativistic Einstein-Klein-Gordon equations to the Schrodinger-Poisson system.

Dark matter plays a fundamental role in theories of the formation and evolution of galaxies. Thus every attempt to model galaxy formation and evolution has to take into consideration the presence of dark halos. Moreover, mergers and accretion appear to be fundamental driving mechanisms in determining the present day properties of galaxies. The aim of this thesis is to study the ultra-fine distribution of dark matter in the Solar neighbourhood, and to investigate the implications for the current and next generation of dark matter directional detectors. For this purpose we develop a model for halo mergers in a Milky Way-like galaxy. The signals expected in lab-based dark matter detection experiments depend on the phase-space distribution on sub-milliparsec scales. With our numerical technique it is possible to resolve structures produced by minor mergers of subhalos with a larger parent halo. This type of substructure is unaccessible to conventional N-body simulations. When applied in a cosmological context,this method becomes a powerful instrument to reproduce and analyse the complete multiple merger history of a Milky Way-like system. The results obtained simulating the Galactic halo suggest that the velocity distribution in the solar neighbourhood after an evolution time corresponding to the lifetime of our galaxy (≃ 14Gyr) is smooth. This result suggests the presence of a huge number of dark matter streams that overlap to form a smooth distribution. Nevertheless, the final velocity distribution has overdensities for all the cases that has been analysed. They are generated by a very large number of merger events, but the current generation of detectors have not the angular resolution required to observe these features. A future generation of detectors with a resolution of ~ 1◦ would start to resolve them, allowing the merger history of the Galaxy to begin to be unravelled using this diagnostic.

This thesis examines many of the ways in which massive galaxies and their super- massive black holes have changed over the past 12 billion years. In a sense, this is an attempt to write a cosmic history of massive galaxies, and in so doing construct a useful catalogue of changes which can be studied to gain insight into galaxy formation and evolution. In particular, this thesis concentrates on two potential drivers for galactic evolution: external influences from galaxy - galaxy interactions (Chapters 2 - 3); and internal influences from AGN feedback (Chapter 4). We find that both of these mechanisms have a profound impact on massive galaxies throughout their lifetimes. In Chapter 2 the major merger history of massive galaxies is probed via close pair statistics and computational morphological approaches. We find that there is a mono- tonic rise in the merger fraction of massive galaxies with redshift out to z = 3, which is best parameterised by a simple power law of the form fm = f0(1 + z)^m, where f0 = 0.008 +/- 0.003 and m = 3.0 +/- 0.4. We compute the total number of major mergers that massive galaxies (with M∗ > 10^11 M⊙) experience from z = 3 to the present to be Nm = 1.7 +/- 0.5. We also note a close accord between morphological and close pair methods at z < 1.5 for standard optically defined CAS mergers and d < 30 kpc close pairs, probably indicative of both methods tracing the underlying merger activity with similar mass ratio and timescale sensitivities. Further, we provide a series of additional tests to the close pair method. In Chapter 3 we extend the study of galaxy interactions to minor mergers, and also compute the morphologically determined major merger fractions of very high redshift massive galaxies. We find that high redshift massive galaxies are frequently highly asymmetric with ∼ 1/4 fitting the CAS definition of a merger at 1.7 < z < 3. We go on to utilise the extraordinary depth and resolution of the HST GOODS NICMOS Survey to probe the minor merger history of massive galaxies. We find that in total massive galaxies experience Nm = (4.5+/-2.1)/τm mergers with galaxies with M∗ > 10^9 M⊙ from z = 3 to the present, where τm is the merger timescale which will vary with mass. From this we compute the total stellar mass increase, due to mergers, of massive galaxies to be ∆M∗ ∼ 3×10^11 M⊙ over the past 12 billion years. This potentially offers a tempting solution for the observed rapid growth of massive galaxies throughout the same epoch. In chapter 4 we investigate in detail the co-evolution of massive galaxies and their supermassive black holes by constructing a complete volume limited sample of 85 AGN with hard band luminosities LX > 2.35 × 10^43 erg s^−1 residing within host galaxies with masses M∗ > 10^10.5 M⊙ at 0.4 < z < 3. Using this data we compute the Eddington limiting (minimum) masses, ME, of the black holes in our sample. By assuming that there is no evolution in the Eddington ratio (μ = LBol/LEdd) and then that there is maximum possible evolution to the Eddington limit, we quantify the evolution in the M∗/MBH ratio as lying in the range 700 < M∗/MBH < 10000, compared to a local value of M∗/MBH ∼ 1000. Furthermore, we find that the active fraction of massive galaxies rises with redshift from 1.2 +/- 0.2 % at z = 0.7 to 7.4 +/- 2 % at z = 2.5. We calculate the maximum timescales for which our sample of AGN can continue to accrete at their observed rates before surpassing the local galaxy-black hole mass relation. We use these timescales to calculate the total fraction of massive galaxies which will be active above our threshold, finding that at least ∼ 40 % of all massive galaxies will be Seyfert luminosity AGN or brighter since z = 3. We find that the energy output due to these objects is sufficient to strip apart every massive galaxy in the universe at least 35 times over. Finally, we use this method to compute the evolution in the X-ray luminosity density of AGN with redshift, finding that massive galaxy Seyferts are the dominant source of X-ray emission in the Universe at z < 3. We conclude in Chapter 5 by summarising these findings and commenting upon the powerful role of both internal and external influences on galaxy formation and evolution over the past 12 billion years.

This thesis investigates the role of environment on galaxy formation and evolution, giving particular focus to the transformation of star forming spirals into passive S0s. The data utilised for this study comes from photometric and spectroscopic observations of galaxies at 0 < z < 1 in different environments from the ESO Distant Cluster Survey. We first study the formation history of (172) cluster ellipticals (Es) and S0s, the oldest types of galaxies in the local universe. We examine their colour-magnitude relation (CMR), and find a very small intrinsic colour scatter. Only 7% of the galaxies are significantly bluer than the CMR. The scarcity of blue S0s indicates that, if they are the descendants of spirals, these were already red when they became S0s. We observe no dependence of the CMR scatter with z or cluster velocity dispersion. This implies that by the time cluster E/S0s achieve their morphology, the vast majority have already joined the red sequence. We estimate the galaxy formation redshift z_F for each cluster and find that while it does not depend on the cluster velocity dispersion, it increases weakly with cluster redshift. This suggests that, at any given z, in order to have a population of fully-formed E and S0s they needed to have formed most of their stars ≃2–4Gyr prior to observation. In other words, the galaxies that already have early-type morphologies also have reasonably-old stellar populations. This is partly a manifestation of the "progenitor bias", but also a consequence of the fact that the vast majority of the E/S0s in clusters (in particular the massive ones) were already red by the time they achieved their morphology. Moreover, E and S0 galaxies exhibit very similar colour scatter, implying similar stellar population ages. We also find that fainter E/S0s finished forming their stars later, consistent with the cluster red sequence being built over time and the brightest galaxies reaching the red sequence earlier than fainter ones. Finally, we find that the E/S0s cluster galaxies must have had their star formation truncated over an extended period ∆t ≿1 Gyr. We then move our focus to the evolution of star-forming galaxies. We investigate the effect of the environment on the transformation of star-forming spirals into passive S0s by studying the properties of the gas and the stars in a sample of 422 emission-line galaxies in different environments. We identify galaxies with kinematical disturbances (in their gas disks), and find that they are more frequent in clusters than in the field. The fraction of kinematically-disturbed galaxies increases with cluster velocity dispersion and decreases with distance from the cluster centre, but remains constant with projected galaxy density. We also studied morphological disturbances in the stellar light, finding that the fraction of morphologically disturbed galaxies is independent of environment. Moreover, there is little correlation between the presence of kinematically-disturbed gas and morphological distortions. For the kinematically-undisturbed galaxies, we find that the cluster and field B-band Tully-Fisher relations are remarkably similar. Additionally, we find that the kinematically-disturbed galaxies show a suppressed specific star formation rate. There is also evidence indicating that the gas disks in cluster galaxies have been truncated, and therefore their star formation is more concentrated than in low-density environments. If spirals are the progenitors of cluster S0s, our findings imply that the physical mechanism transforming cluster galaxies efficiently disturbs the star forming gas and reduces their specific star formation rate. This star-forming gas is either removed more efficiently from the outskirts of the galaxies or it is driven towards the centre (or both). In any case, this makes any remaining star formation more centrally concentrated, helping to build the bulges of S0s. All this evidence, together with the fact that the transformation mechanism does not seem to induce strong morphological disturbances on the galaxies, suggests that the physical processes involved are related to the intracluster medium, with galaxy-galaxy interactions playing only a limited role in clusters. Interestingly, in analogy with the "blue" early-type galaxies found in the CMR study in clusters, we have also found several emission-line E/S0 galaxies with extended rotating star-forming gas disks.

Studies of the history of the Universe are for a large part concerned with mapping the evolution of galaxies over cosmic time. Beginning from the seeds of density perturbations in the early Universe, and building up through gravitational and astrophysical interactions to form the wide diversity seen in the present day, galaxies allow us to observe the distribution of luminous (and dark) matter over a wide range of look-back times. A key process in galaxy evolution is the formation of stars, an activity which is readily observed by indirect means, although the detailed mechanism is not fully understood. One of the most successful methods for tracing star formation is to observe the emission from dust in galaxies. These tiny particles of carbon- and silicon-based solids resemble smoke, pervading the interstellar medium in many (if not all) galaxies, and blocking the short-wavelength radiation from hot, newly-formed stars. They re-radiate this energy as far-infrared radiation (wavelengths ~10-1000 microns), which can be detected from sources throughout the Universe by telescopes such as the Spitzer and Herschel space observatories. The spectral form of this radiation varies from one galaxy to another, depending on many factors such as the activity within the galaxy, the amount of dust, and the sources heating the dust. Hence, with careful interpretation, we can use these observations to trace the star-forming activity and dust mass in different types of galaxies from early times through to the present day. In this thesis I describe three projects, each of which utilises multi-wavelength datasets from large surveys to probe the dust emission from samples of galaxies at different cosmic epochs, and explore the relationship between dust emission and other galaxy properties. The first project samples the most massive galaxies at a range of redshifts spanning the peak era of star formation, and investigates the correlation between far-infrared and radio emission. I use a `stacking' methodology to avoid bias towards the brightest star-forming galaxies, and show that the far-infrared and radio tracers of star formation agree up to high redshifts in typical massive galaxies. In the second project I apply the stacking method to a large sample of low-redshift galaxies selected from a major optical survey spanning the last four billion years of evolution. I make use of the largest ever sub-millimetre imaging survey to produce a detailed and unbiased census of the dust mass in ordinary galaxies as a function of optical brightness, colour and look-back time. I show that the luminosity and temperature of dust is a strong function of galaxy mass and colour, while the dust masses of all galaxy types have decreased rapidly over the time span probed. The final project focuses on a small sample of nearby galaxies and utilises data obtained and reduced by myself to probe the molecular-gas content of galaxies selected to have large dust masses. This study addresses questions about how well the cold dust, traced by the sub-millimetre wavebands of Herschel, is correlated with the cold gas, which provides the fuel for ongoing star formation. The thesis demonstrates the utility of statistical techniques for large surveys, and also contains aspects of data reduction and extensive discussion of the astrophysical interpretation of results. Through these various analyses I show that dust emission can provide a valuable window on the growth of galaxies through star formation. The work contained herein represents significant progress in the field of observational extragalactic astronomy, including work recently published in the scientific literature in two collaborative research papers led by myself, in addition to a third paper that I am currently preparing.

Based on a number of experimentally verified physical observations, it is argued that the standard principles of quantum mechanics should be applied to the Universe as a whole. Thus, a paradigm is proposed in which the entire Universe is represented by a pure state wavefunction contained in a factorisable Hilbert space of enormous dimension, and where this statevector is developed by successive applications of operators that correspond to unitary rotations and Hermitian tests. Moreover, because by definition the Universe contains everything, it is argued that these operators must be chosen self-referentially; the overall dynamics of the system is envisaged to be analogous to a gigantic, self-governing, quantum computation. The issue of how the Universe could choose these operators without requiring or referring to a fictitious external observer is addressed, and this in turn rephrases and removes the traditional Measurement Problem inherent in the Copenhagen interpretation of quantum mechanics. The processes by which conventional physics might be recovered from this fundamental, mathematical and global description of reality are particularly investigated. Specifically, it is demonstrated that by considering the changing properties, separabilities and factorisations of both the state and the operators as the Universe proceeds though a sequence of discrete computations, familiar notions such as classical distinguishability, particle physics, space, time, special relativity and endo-physical experiments can all begin to emerge from the proposed picture. A pregeometric vision of cosmology is therefore discussed, with all of physics ultimately arising from the relationships occurring between the elements of the underlying mathematical structure. The possible origins of observable physics, including physical objects positioned at definite locations in an arena of apparently continuous space and time, are consequently investigated for a Universe that incorporates quantum theory as a fundamental feature. Overall, a framework for quantum cosmology is introduced and explored which attempts to account for the existence of time, space, matter and, eventually, everything else in the Universe, from a physically consistent perspective.

This thesis examines the evolution of massive disc galaxies as a function of cosmic time and environment by analysing a sample of luminous disc galaxies, located in the field and rich clusters at intermediate redshifts. The data utilised for this study are two-dimensional optical spectra obtained with the FORS2 instrument on the VLT, along with imaging from a variety of sources. From these we measure absolute rest-frame B-band magnitudes, stellar scalelengths (r_d,phot), rotation velocities (V_rot), emission-line scalelengths (r_d,spec) and emission-line equivalent widths, resulting in estimates of gas-phase oxygen abundance, current star formation rate (SFR) and dust extinction. We investigate evolution of the field Tully-Fisher relation (TFR) using a sample of 89 galaxies covering the redshift range 0.1-1. We find evidence that these luminous spiral galaxies are increasingly offset from the local TFR with redshift, reaching a brightening of -1.0+-0.5 mag, at a given V_rot, by z ~ 1. We argue that, due to likely selection effects, this observed evolution represents an upper limit. Previous studies have used an observed correlation between TFR residuals and V_rot to argue that low mass galaxies have evolved significantly more than those with higher mass. However, we demonstrate that such a correlation does not necessarily indicate a physical difference in the evolution of galaxies with different V_rot. Interpreting the luminosity evolution derived from the TFR as due to evolution in the SFR of these luminous spiral galaxies, we find that SFR(z) is proportional to (1+z)^(1.7+-1.1). Although the uncertainties are large, this evolution, which is probably an upper limit, appears to be slower than that derived for the overall field galaxy population. This suggests that the rapid evolution of the SFR density of the universe observed since z ~ 1 is not in general driven by the evolution of the SFR in individual bright spiral galaxies. The measured emission-line equivalent widths, diagnostic ratios, oxygen abundances, star formation rates and dust extinctions for a sample of 40 luminous, massive (V_rot > 80 km/s), star-forming, field disc galaxies, with redshifts z=0.2-0.8, cover similar ranges to those observed across a large sample of local galaxies. However, at a given galaxy luminosity, many of our galaxies have oxygen abundances significantly lower than local galaxies with similar luminosities. The galaxies in this luminous, metal-poor subsample exhibit physical conditions similar to those of local faint and metal-poor star-forming galaxies. Lower-metallicity systems are ~2 mag brighter, and have star formation rates an order of magnitude higher, compared with similar metallicity galaxies today. Oxygen abundances are not found to correlate with the emission scale length size of galaxies, and the rotation velocity--metallicity relation, while perhaps present, is unclear. This suggests that massive field galaxies at intermediate redshifts are diverse in terms of their interstellar gas properties and stellar content. To examine variations in the TFR with environment, matched samples of 58 field and 22 cluster galaxies are constructed, selected in a homogeneous manner and covering similar ranges in redshift (0.25 < z < 1.0) and luminosity (M_B < -19.5 mag). The distributions of M_B, V_rot and scalelength are found to be comparable for the two samples. However, we find that the TFR of the cluster galaxies is systematically offset with respect to the field sample by -0.7+-0.2 mag. This offset is significant at 3-sigma and persists when we account for an evolution of the field TFR with redshift. Tests are performed to investigate potential differences in the observed emission lines and derived parameters of the cluster and field samples. However, no such differences which could account for the offset are found. Offsets are also found between cluster and field samples in the relations of M_B and V_rot versus r_d,phot and r_d,spec, although these are difficult to interpret. Our cluster galaxies are found to have ratios of emission-line to stellar scalelengths (r_d,spec / r_d,phot) significantly lower than for our field galaxies: 0.88 +- 0.08 versus 1.15 +- 0.05, respectively. This indicates that star formation is more centrally concentrated in the cluster galaxies. The comparison of interstellar gas properties between 16 bright, star-forming, cluster disc galaxies at intermediate redshifts (0.3 < z < 0.6, <z> = 0.42) and their counterparts in the coeval field, reveals that both samples are generally similar. However, on average the cluster galaxies have emission-line equivalent widths that are significantly lower than for the field galaxies. A contrasting fraction of the distant cluster galaxies, though, appears to have much higher emission-line equivalent widths, comparable to the highest seen in the field. This tentatively implies a bimodality in the star formation rates per unit luminosity of distant cluster galaxies, which is not present for our field sample. However we find no substantial difference in the long term star formation histories of these cluster and field galaxies, as indicated by their gas-phase metallicities. The most likely explanation for the results of our cluster versus field comparison is that spiral galaxies entering intermediate-redshift clusters often experience a short-lived enhancement of their star formation rate, followed by a decline, which we would expect to be accompanied by a transformation to S0 morphology.

In this thesis I use the UKIDSS Ultra-Deep Survey to investigate the evolution in clustering of the galaxy population across the redshift range $0<z<3$. Selected in the K-band, the sample does not suffer as greatly from biases against passive and dusty objects that plague optically-selected samples, and so represents the first analysis of a relatively unbiased galaxy sample above z=1. The unique combination of area (0.77 sq. deg.) and depth (K(AB)<24) allows the analysis of both rare, intrinsically bright objects and faint objects, reaching ~L* at z=3. The UDS data are complemented by similarly deep optical data from Subaru and mid-infrared data from Spitzer. These data have enabled accurate photometric redshifts to be computed, which are used extensively throughout this thesis. The combined optical and infrared data are used to firstly select passive and star-forming samples over a wide range in redshift 1<z<2.5. The results of their number counts and clustering properties motivate a more in-depth study of the respective clustering strengths of passive and star-forming galaxies. The main result of this thesis is that passive galaxies are found to be more strongly clustered than star-forming galaxies to at least z=1.5, irrespective of rest-frame K-band luminosity. Furthermore, within either the passive or star-forming sample, luminosity segregation is found to be very mild. These results therefore indicate that even at fixed stellar mass, passive galaxies are more strongly clustered. Clustering strength is directly related to the mass of the typical host dark matter halo. Galaxies which are observed to be passive at z<1.5 are therefore hosted by more massive halos than their star-forming counterparts. This finding is consistent with downsizing in galaxy formation. Downsizing is also found in the clustering strengths of the star-forming sub-samples. The correlation lengths of star-forming galaxies smoothly decline towards z=0. Galaxies of a given K-band luminosity or stellar mass are therefore found in less massive halos in the low-redshift universe. Passive galaxies on the other hand appear to have constant r0 values over 0<z<1.5. If confirmed, this may indicate a preferred mass of dark matter halo for the transition from star-forming to passive. Above z=1.5 the clustering strengths of passive and star-forming galaxies are found to be more similar. If this trend continues it suggests that they may become equal within 2<z<3. This would therefore constitute the epoch over which the passive/star-forming bimodality becomes distinct. These results are then examined more closely in a marked-correlation function analysis and tested against the one of the latest theoretical galaxy formation models. Due to difficulties in defining a suitable quantity for `passivity' from photometric data, the results from the marked correlation functions are largely inconclusive at this stage. However, the potential in their future use is demonstrated. My results highlight two known issues in the semi-analytic galaxy formation model: the over-production of high-redshift sources and red satellites. In addition I offer tentative evidence for further possible discrepancies, in clustering properties at high-redshift.

In this thesis, we explore the effect of the galaxy environment on the physical size and structure of the stellar distribution for relatively local galaxies (z < 0.3) using Hubble Space Telescope/Advanced Camera for Surveys imaging and data from the Space Telescope A901/2 galaxy evolution survey (STAGES). We determine the effect of the environment on the size of the stellar distribution (i.e. galaxy sizes) by comparing the stellar-mass-size relations in the field and cluster environments for different Hubble-type morphologies. For elliptical, lenticular, and high-mass (M* > 10^10 M_sun) spirals, we find no evidence to suggest that a galaxy's size (i.e. effective radius a_e) is dependent on the environment. This result suggests that internal drivers are responsible for any potential size evolution inherent to these galaxies. However, for intermediate-/low-mass spirals (M* < 10^10 M_sun) we do find some evidence for a possible environmental effect, with the mean galaxy size (<a_e>) being ~15-20 per cent larger in the field than in the cluster. This result is driven by a population of low-mass, large-a_e field spirals (observed to contain extended stellar discs) that are largely absent from the cluster environments. This difference implies that the fragile extended stellar discs of these spiral galaxies may not survive the environmental conditions in the cluster. We expand on this result by investigating the effect of the environment on the structure of galactic discs in spiral and S0 galaxies. Using V-band radial surface brightness mu(r) profiles, we identify break features in the stellar disc (down-bending break - truncation; up-bending break - antitruncation) and evaluate their dependence on the galaxy environment. For both spiral and S0 galaxies, we find no evidence to suggest an environmental dependence on the frequency of these break features. We also find no evidence to suggest an environmental dependence on the scalelength h of pure exponential discs, or the break strength T (outer-to-inner scalelength ratio) of broken exponential discs. These results indicate that the stellar distribution in the outer regions of spiral/S0 galaxies is not significantly influenced by the galaxy environment. In our structural analyses, one interesting observation was that truncated mu(r) profiles (down-bending breaks) are very rare in S0s; whereas in spiral galaxies they are commonplace. We expand on this result by comparing the structural properties of the disc (scalelength h, break strength T, break surface brightness mu_brk) in spiral and S0 galaxies. In these comparisons, we find no evidence to suggest that the scalelength h of pure exponential discs or the break surface brightness mu_brk of broken exponentials is dependent on the galaxy morphology. However, we do find some evidence to suggest that the break strength T is smaller (weaker) in S0s compared to spiral galaxies. This result suggests that some process inherent to the morphological transformation of spiral galaxies into S0s does affect the structure of the stellar disc causing a weakening of mu(r) breaks and may even eliminate truncations from S0 galaxies. In additional structural comparisons, we also find that the fraction of exponential bulges is the same (~20 per cent) in both spiral and S0 galaxies, suggesting that major mergers are not driving this transformation. Finally, we complement our structural analyses with an assessment of whether the excess light in the outer regions of antitruncated (up-bending) mu(r) profiles is caused by an outer exponential disc or an extended spheroidal component: we use bulge-disc decomposition in order to achieve this. For spiral galaxies, in the vast majority of cases, evidence indicates that the excess light at large radii is related to an outer shallow disc. We thus conclude that in the majority of spiral galaxies, antitruncated outer stellar discs cannot be explained by bulge light and thus remain a pure disc phenomenon. However, for S0s, bulge light can have a significant effect in the outer regions of the mu(r) profile. In approximately half of S0 antitruncations, the excess light at large radii can be entirely accounted for by light from an extended spheroidal component. These results suggest that as a galaxy evolves from a spiral into an S0, the galaxy naturally evolves into a more bulge-dominated system. We suggest a fading stellar disc (e.g. caused by gas stripping and the termination of star formation) is consistent with this result. In conclusion, our environmental studies indicate that the environment has little direct affect on the size and structure of a galaxy's stellar distribution. This result implies that physical processes directly affecting the structure of the stellar distribution (e.g. mergers or harassment), are not driving the observed morphology-density relation. With respect to both our environmental and morphological studies, we can conclude that more subtle processes acting on the gaseous component of a galaxy (e.g. ram-pressure stripping) are more likely to play an important role in the origin of the morphology-density relation and the transformation of spirals into S0s.

Submillimetre galaxies are an important element in the history of the universe. There have been great advances in technology in the last ten years that have enabled deeper and more detailed investigations of these distant objects. In thisthesis I describe investigations of the properties of high redshift submillimetre galaxies made using data from multiple surveys and multiple instruments. Firstly I describe the process involved in reducing AzTEC data to produce images. I then present the reduced maps and compare them, along with a source catalogue, to those produced by the AzTEC instrument team. I found both reductions produce broadly similar results with some differences that can be explained by slightly different sets of input maps. I then present an analysis of the fainter objects in one of the AzTEC fields using a stacking technique. This analysis determines the contribution Spitzer detected galaxies make to the background at 1.1mm, the redshift dependence of this contribution and the average dust mass that can be associated with it. I also describe an analysis of the ux ratios Eales et al. (2003)found using the available AzTEC data and Spitzer IRAC imaging. In the the penultimate chapter I describe the frequentist identification technique I used to determine counterparts to SCUBA submillimetre sources in the CUDSS three hour field using Spitzer infrared data.