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Galaxy evolution is an interplay of physical processes across a wide range of cosmological size scales, from star formation and black hole growth on sub-pc scales, to interactions with their environments on Mpc scales. The region surrounding individual galaxies within their host halos is known as the Circumgalactic Medium (CGM), and connects galaxies to the wider Intergalactic Medium (IGM). The CGM acts as both a reservoir of inflowing gas and a repository for outflowing gas as it is transported outwards via galactic feedback. Quasar absorption line surveys have revealed the CGM to be a complex, multiphase environment in which ions tracing cool and hot gas are present within the same absorber systems. Cosmological simulations are a powerful tool for building a theoretical understanding of these interconnected processes and resulting observations. They provide a 3D view of galaxies and their host halos, in which we intrinsically know the physical conditions of the constituent dark matter and baryons. As such, simulations are useful both for testing galaxy evolution models against the real universe, and for interpreting complex observations in a physical context. In this thesis I present detailed comparisons of simulations to observations of star formation and quenching in galaxies, and of absorbers in galactic halos in an effort to constrain physical models. I use Simba, a suite of state of the art cosmological simulations with realistic sub-grid physical models based on high resolution zoom simulations, including novel treatments of dust evolution and of black hole growth and feedback. I investigate the nature of gas in galaxies and their halos, and show comparisons with observations. In addition, I isolate the impacts of galactic feedback and ionising radiation on the results by varying elements of the input physical models. In Chapter 3, I present radial profiles of star forming and green valley galaxies in Simba at z=0 and compare with observations of MaNGA spatially resolved spectroscopy. My analysis shows strong central depressions in star formation rate (SFR), specific SFR (sSFR), and gas fraction in Simba's green valley galaxies and massive star-forming systems, qualitatively as observed, owing to Active Galactic Nuclei (AGN) X-ray feedback, which pushes central gas radially outwards. These effects are less pronounced at higher redshift, owing to less powerful AGN feedback. I also present a comparison of galaxy half light radii to observations at various redshifts, finding that predictions for star-forming galaxy sizes are accurate but that quenched galaxies are impacted by numerical heating. In Chapter 4, I characterise the low redshift CGM in Simba and examine the impact of differing feedback prescriptions. Low mass galaxies live in multiphase, diverse halos, whereas high mass galaxies live in halos dominated by hot gas. Halo baryon fractions are generally < 50% of the cosmic fraction due to stellar feedback at low masses, and 'jet-mode' AGN feedback at high masses. I present a comparison of absorption statistics to the COS-Halos and COS-Dwarfs surveys: Simba reproduces HI absorption well around star forming galaxies and broadly reproduces absorption of selected metal lines, including the observed dichotomy in OVI absorption between star forming and quenched galaxies. These predictions of metal line absorption are sensitive to the choice of photo-ionising background. Varying the galactic feedback prescription shows that stellar feedback enriches the CGM, while AGN feedback sets the gas temperature phase. In Chapter 5 I extend this analysis with a theoretical perspective of the CGM in Simba using a sample of CGM absorbers from a representative sample of Simba galaxies, selected across a range of stellar masses and sSFR. Absorbers are more abundant around low mass, star forming galaxies; the CGM of green valley galaxies is more similar to that of quenched galaxies. The absorber overdensity depends on the sSFR of the galaxy, while the absorber temperature is set by galaxy stellar mass. Absorption from low ions arises from cold, dense CGM gas, whilst absorption from higher ions traces hotter, more diffuse gas. I also examine the proportion of absorption arising from collisionally ionised gas, and from gas that is associated with satellite galaxies. Finally, in Chapter 6 I develop a tree-based machine learning mapping between the observable properties and the underlying physical conditions of the absorbers in the CGM absorber sample from Chapter 5. Such a mapping has the potential to be used to interpret CGM observations within a full cosmological context, assuming the Simba galaxy evolution model.

The study of gaseous haloes holds the key to understanding gas flows in and out of galaxies, which in turn determines how galaxies form and evolve. However, recent observations have revealed them to be very complex, with the presence of significant amounts of multiphase gas, driven by a range of physical process within galaxies as well as by the larger-scale environment. Simulations that realistically model this gas are therefore crucial to interpreting this new data, and ultimately helping us understand how galaxies assemble. However, many cosmological simulations sacrifice resolution in gaseous haloes to reduce their computational cost, meaning their ability to accurately resolve some of the key physical processes, such as turbulence and instabilities, can be limited. Using cosmological simulations, in this thesis I have investigated how gaseous haloes evolve over time. I have implemented a new shock refinement scheme to boost numerical resolution in gaseous haloes. Applied to a massive cluster progenitor, I found significant increases in cold gas mass in filaments and clumps, leading to more widespread star formation. In the hot halo there is a notable boost in turbulent velocities, leading to a doubling of non-thermal pressure support. With the FABLE suite, I studied how the hydrostatic mass bias and turbulent pressure support level in galaxy clusters change as they undergo major mergers and are host to powerful feedback episodes. I found that clusters rarely tend to be in hydrostatic equilibrium for long, with variations being driven by both merger activity and interestingly, at higher redshift, AGN feedback. Such insights could be important for future cluster mass estimates from X-ray and SZ observations, for use as cosmological probes. Finally, I simulated the growth of an ultramassive black hole of mass ∼ 10^10 M⊙ by z = 6. I have studied its impact on the gaseous halo around it, including how powerful AGN feedback can disrupt inflowing cold filaments and increase the thermal pressure of the surrounding gas. I found that strong AGN-driven outflows can deposit significant quantities of metals at very large distances from the central galaxy, which could be a unique signature of the presence of such ultramassive black holes in the very early Universe. Many of the effects predicted by the simulations described in this thesis have the potential to be observed (or ruled out) in the coming decade or two, with an incoming wealth of observational data from observatories like JWST, Athena, CMB-S4, SKA, and LISA. These data, combined with further developments in theory and simulation, will therefore revolutionise our understanding of gaseous haloes.

Understanding the physical processes responsible for ceasing, or 'quenching', star formation in galaxies is one of the most important unsolved questions in the field of galaxy evolution. Over the past two decades multiple mechanisms were suggested as potential drivers of the transition between the star-forming and quiescent galaxy categories, painting a very complex picture of quenching and its potential physical drivers. In this thesis we take on the challenge of identifying and characterising the physics of galaxy quenching by combining traditional statistical methods with machine learning techniques to embrace the complexity of all physical processes at play. We first show how both gas fraction and star formation efficiency (SFE) decrease in Sloand Digital Sky Survey (SDSS) galaxies at z = 0 as they depart from the star-forming Main Sequence (MS) towards quiescence. We further show that both quantities correlate similarly strongly with the departure from the MS, implying the need for any physical model of quenching to invoke a change in both gas fraction and SFE. We then move on to extract theoretical predictions of the observable consequences of Active Galactic Nucleus (AGN) feedback quenching from three state-of-the-art cosmological simulations: EAGLE, Illustris and IllustrisTNG. Our machine learning (ML) classification reveals supermassive black hole mass (MBH) as the most predictive parameter in determining whether a galaxy is star forming or quenched at redshift z = 0 in all three simulations. This prediction is met overwhelmingly well in the observations, where it is true for a range of indirect estimates of MBH via proxies as well as its dynamical measurements. In simulations we further demonstrate that it is the integrated power output of the AGN, rather than its instantaneous activity, which causes galaxies to quench. We thus mark our most important contribution to the field by providing direct evidence in favour of the AGN quenching paradigm, together with suggestions on how to best observe the effect supermassive black holes have on their galactic hosts. Finally, we analyse the trends in molecular gas content with MBH, finding that the SDSS observations more closely follow trends predicted by IllustrisTNG, rather than the Illustris suite. In our current ongoing work we also analyse spatially resolved properties of the cold ISM, rigorously testing the ability of current cosmological simulations to successfully recover realistic ISM on kpc scales. As a result of our study we further conclude that a viable AGN feedback prescription can be achieved by a combination of preventative feedback and turbulence injection which together quench star formation in central galaxies.

Over the past two decades, detailed studies in the nearby Universe have shown that accreting supermassive black holes (SMBHs; or active galactic nuclei; AGN) can have a significant effect on their host galaxies, suppressing star formation and regulating their growth (known as AGN feedback). One of the most striking examples of AGN feedback in action comes from detailed studies of local AGN which exhibit powerful bi-polar jet outflows that can deposit significant energy into the galaxy halo, heating the surrounding gas and thereby regulating their own growth and suppressing star-formation activity. Therefore, studying the properties of AGN and the galaxies in which they reside is crucial in understanding and further developing our current models of galaxy formation and evolution. AGN can be split into two distinct categories, based on the accretion efficiency of the SMBH: radiative-mode AGN, and jet-mode AGN. Radiative-mode AGN are associated with efficient accretion, typically from cold gas, resulting in the formation of a geometrically thin, optically thick accretion disk that is typically surrounded by a dusty obscuring structure; these AGN are known to drive powerful outflows. Jet-mode AGN are associated with inefficient accretion, typically from hot gas, and display powerful bi-polar synchrotron radio jets that emit the bulk of their energetic output into the surrounding medium in the form of mechanical energy; these AGN are identified as such based on radio observations, showing no signs of AGN activity (e.g. accretion disk or torus) at other wavelengths. Based on the nature of the excitation lines, the jet-mode and radio-loud radiative-mode populations are also known as low-excitation radio galaxies (LERGs) and high-excitation radio galaxies (HERGs), respectively. However, our understanding of these AGN and their feedback effect is built primarily from detailed local Universe observations. Determining the physical mechanisms underpinning triggering and fuelling of AGN and how this affects AGN feedback activity across cosmic time is crucial but lacking. In this thesis, I address this shortcoming using deep observations carried out by the LOw Frequency ARray (LOFAR) telescope: the LOFAR Deep Fields; this forms the deepest radio continuum survey to date at low frequencies. I generated key science-enhanced datasets using this survey and studied the cosmic evolution of AGN feedback from low-luminosity radio-AGN within the past 10 Gyrs and how this feedback affects the growth and evolution of galaxies. In the first science chapter of the thesis, I detail the pipeline I developed to generate new, more robust multi-wavelength catalogues in the LOFAR Deep Fields. The existing catalogues in the literature either did not include the deepest available datasets in each survey field, or were created using different methodologies for detecting sources and measuring their fluxes; all this meant the catalogues were not sufficiently robust for the scientific aims of the thesis. To overcome these issues, I generated new catalogues in two of the Deep Fields by combining information from the ultraviolet to the mid-infrared wavelengths to detect sources and extract their properties in a clean and homogeneous manner. These are some of the best-studied regions of the sky and therefore these catalogues are also expected to provide a legacy value beyond the aims of the LOFAR surveys. Then, in the next chapter, using the multi-wavelength catalogues generated, I identify the host-galaxy counterparts of the radio-detected sources in the LOFAR Deep Fields. Host-galaxy identification and characterisation is crucial, in particular for radio surveys, in determining the photometric redshifts and physical properties (e.g. stellar masses, luminosities, star-formation rates) of the radio-source host galaxies, greatly expanding the scientific scope of the survey. I identified the host-galaxy counterparts of the LOFAR sources using a combination of the statistical Likelihood Ratio method and a visual classification scheme, using a workflow to decide the most appropriate method of identification for each source. This process results in a value-added catalogue of over 80 000 radio sources with multi-wavelength counterparts identified for > 97% of them. In this chapter, I then also investigate the properties of host galaxies of the faint radio population in the LOFAR Deep Fields. In the fourth chapter I focus on studying the evolution of the radio-AGN population and their properties in the LOFAR Deep Fields and how feedback from these AGN evolves across cosmic time. Of particular interest, and the focus of this chapter are the LERGs, which dominate at low radio luminosities and are thought to play a key role in the formation of massive galaxies in the local Universe; however, the evolution of this population beyond z ∼ 1 is not well known. In this chapter, I present the first robust measurement of the LERG luminosity functions out to z ∼ 2.5 and characterise the evolution of their host galaxy properties. This population shows relatively mild evolution across the redshifts examined; this is explained by the different evolution of the LERGs hosted in star-forming galaxies and those hosted in quiescent galaxies. The evolution of the quiescent LERGs show a strong decline in their space densities with increasing redshift, in accordance with the available host galaxies, while there is also an increase in the characteristic luminosity. I also find that unlike in the local Universe, the bulk of the LERGs are hosted by star-forming galaxies at higher redshifts and that the AGN in these galaxies appear to be fuelled by a different mechanism, likely associated with the cold gas, as compared to the LERGs in quiescent galaxies. In the final chapter I present the conclusions and look towards further exploration of this dataset. In particular, I discuss the characterisation of 3% of the radio-sources that were found to be completely invisible at optical and near-infrared wavelengths; an investigation of the far-infrared and radio properties of this subset found that the vast majority of these sources are likely high-redshift star-forming galaxies hosting a radio-AGN. To understand the nature of these extreme sources at early epochs, I present preliminary analysis from recent sub-millimetre follow-up via the sub-millimetre array (SMA) and the James Clerk Maxwell Telescope (JCMT). In addition, I also discuss the spectroscopic follow-up of the radio-AGN population found in the previous chapter with the upcoming multi-object WEAVE spectrograph on the William Herschel Telescope to study the prevalence of AGN activity as a function of different galaxy properties out to high redshifts. Finally, I also describe plans to compare the observational results found in the previous chapters with predictions from the latest cosmological simulations.

A number of theoretical mechanisms have been invoked to explain the transformation of star forming galaxies into quenched galaxies, such as the removal of gas by active galactic nuclei- (AGN) and star formation-driven galactic outflows, and the heating of the galaxy halo and subsequent halting of gas accretion caused by virial shocks and preventative AGN feedback. Nonetheless, we still lack a clear understanding of which mechanism is the most important for quenching galaxies. The goal of this thesis is to study galaxy quenching from an observational perspective and to address the following question: why do galaxies stop forming stars? In the first part of this thesis I examine the relationship between molecular gas (observed with ALMA and NOEMA) and star formation on spatially resolved scales in seven green valley MaNGA galaxies. I find that both the star formation efficiency (SFE) and gas fraction of green valley galaxies is suppressed relative to typical star forming galaxies. These two effects are equally important for suppressing star formation in the outer disc, but it is not possible to rank their effect towards the strongly quenched galaxy centre, where SFE is only constrained to an upper limit. I also show that the significant reduction in gas fraction in the central regions is driven by an increase in stellar mass surface density rather than a decrease in molecular gas surface density, which disfavours quenching mechanisms that eject gas from galaxies. In the second part of this thesis I develop a 2D inclined rotating disc model to estimate the kinematic properties of 1862 MaNGA galaxies, and I use a random forest analysis to explore the relationship between galaxy kinematics and quenching. I find that the average velocity dispersion is overwhelmingly the most important kinematic parameter for predicting galaxy quenching. Furthermore, a full and partial correlation analysis shows that many commonly discussed correlations between galaxy properties (such as stellar mass) and quenching are spurious, and indeed at fixed velocity dispersion these correlations are almost entirely removed. I interpret this finding in the context of the BH-σ relation and argue for a scenario in which quenching occurs due to preventative feedback from AGN. In the third part of this thesis I attempt to directly probe preventative feedback from AGN by analysing a deep ALMA band 4 observation of HE0515-4414 to search for the Sunyaev-Zel'dovich (SZ) signal tracing the quasar's hot halo gas. I find marginal evidence (~3.3σ) of large scale (~300 kpc) heating in the visibility plane, as well as ~3.2σ evidence of localised heating to the south west of the central quasar in the image plane. Furthermore, I use SZ maps from the FABLE simulation to demonstrate that ALMA and the ACA are effective at detecting the SZ signal in band 3, and I discuss the optimal strategy for future observations.

The study of galaxy formation and evolution is a cornerstone in astrophysics, as galaxies connect together all scales of the Universe. The physical processes that govern galaxies therefore needs to be fully understood if we are to understand how our Universe works. The various morphologies of galaxies we see today indicate that there are multiple processes at play, that act both on and within galaxies. In our currently accepted paradigm, galaxies are expected to assemble mass through merging and gas accretion, therefore these are critical processes that must be understood across the range of galaxy masses. We can now combine observational data from wide-are surveys with state of the art cosmological simulations to study how these processes drive galaxy evolution across cosmic time. In this thesis we have used cosmological simulations (Horizon-AGN and NewHorizon) to study how physical processes shape galaxies. Firstly, we explore an unusual population of extremely massive (M∗ >1011M0) spheroids, in the Horizon-AGN simulation, which exhibit anomalously low ex-situ mass fractions. This indicates that they form without recourse to significant merging, contrary to the common belief. These systems form in a single minor-merger event (with typical merger mass ratios of 0.11 - 0.33), where the satellite orbit is virtually co-planar with the disc of the massive galaxy. The merger triggers a catastrophic change in morphology, over only a few hundred Myrs, coupled with strong in-situ star formation. While this channel produces a minority (∼5 per cent) of such galaxies, our study demonstrates that the formation of at least some of the most massive spheroids need not involve major mergers - or any significant merging at all - contrary to what is classically believed. We also look at how extremely massive disc galaxies form in both simulations and in the nearby Universe. We show that extremely massive (M∗ > 1011.4 M0) discs are created via two channels. In the primary channel (accounting for 70% of these systems and 8% of massive galaxies) the most recent, significant merger (mass ratio > 1:10) between a massive spheroid and a gas-rich satellite 'spins up' the spheroid by creating a new rotational stellar component, leaving a massive disc as the remnant. In the secondary channel (accounting for 30% of these systems and 3% of massive galaxies), a system maintains a disc throughout its lifetime, due to an anomalously quiet merger history. These massive discs have similar black-hole masses and accretion rates to massive spheroids, providing a natural explanation for why some powerful AGN are surprisingly found in disc galaxies. In an observational follow-up we use UV-optical and HI data of massive galaxies, from the SDSS, GALEX, DECaLS and ALFALFA surveys to test the predictions from Horizon-AGN. Observed massive discs form ∼13 per cent of the population, in good agreement with the simulation (∼11 per cent). ∼64 per cent of massive discs exhibit tidal features indicative of recent minor mergers in the deep DECaLS images. The incidence of these features is at least four times higher than in low-mass discs, indicating that minor mergers play a significant role in the formation of these systems. The empirical star-formation rates agree well with Horizon-AGN's predictions and, for a small galaxy sample with HI detections, the HI masses/fractions are consistent with the range predicted. The good agreement between theory and observations indicates that extremely massive discs are indeed remnants of recent minor mergers between spheroids and gas-rich satellites. We also look into the origins of dwarf low surface brightness galaxies (LSBGs), which are expected to dominate the galaxy number density. Using NewHorizon, a high-resolution cosmo- logical simulation, we study the origin of LSBGs and explain why, at similar stellar mass, they exhibit a large observed spread in surface brightness. NewHorizon galaxies populate a well- defined locus in the surface brightness - stellar mass plane, with a spread of ∼3 mag arcsec−2, in agreement with deep SDSS Stripe data. We find that galaxies with fainter surface brightnesses today are born in regions of higher dark-matter density. This results in faster gas accretion and more intense star formation at early epochs. The stronger resultant supernova feedback flattens gas profiles at a faster rate which, in turn, creates shallower stellar profiles (i.e. more diffuse systems) more rapidly. A small minority of dwarfs depart from the main locus towards high surface brightnesses, making them detectable in past wide surveys (e.g. standard-depth SDSS images). These systems have anomalously high star-formation rates, triggered by recent, fly-by or merger-driven starbursts. We note that objects considered extreme/anomalous at the depth of current datasets, e.g. 'ultra-diffuse galaxies', actually dominate the predicted dwarf population and will be routinely visible in future surveys like LSST. Finally, we look at a population of galaxies that go against our current theoretical paradigm. Recent observations have found local dwarfs with extremely low dark matter content, potentially bringing the validity of the standard model into question. We use NewHorizon to demonstrate that sustained stripping of dark matter, in tidal interactions between a massive galaxy and a dwarf satellite, naturally produces dwarfs that are dark-matter-deficient. The degree of stripping is driven by the closeness of the orbit of the dwarf around its massive companion, and produces dwarfs with halo-to-stellar mass ratios consistent with the findings of recent observational studies. ∼30 per cent of dwarfs show some deviation from normal dark matter fractions due to dark matter stripping, with 10 per cent showing high levels of dark matter deficiency (Mhalo/M*<10). The creation of these galaxies is, therefore, a natural by-product of galaxy evolution and their existence is not in tension with the standard paradigm. This thesis examines galaxy populations that appear to go against the currently accepted paradigm, in both the massive and dwarf galaxy regime. We show that galaxy evolution is a very complicated problem and that it is possible to form different galaxy populations through many processes. By using a cosmological simulation based on ACDM we also show that the existence of these populations do not pose a challenge to this model and are, in fact, readily explained by it.

We are now in an era of spatially resolved spectroscopic observations for thousands of galaxies. Labelled integral field spectroscopy, a natural product is detailed kinematics of both stars and gas enabling accurate estimators of a galaxy's angular momentum, and hence, kinematic classifications. This presents a significant step forward in how we understand and classify galaxies, previously being reliant on their visual form; morphology. In tandem, significant progress has also been made in theory with realistic, cosmological simulations becoming a reality. These high resolution simulations, coupled with hydrodynamics, have produced populations of thousands of galaxies; replicating a wide variety of properties of actual galaxies in our observable Universe. Both will be crucial in further understanding how galaxies evolve to what we find in the local Universe. This thesis uses the natural synergy between integral field spectroscopy and cosmological hydrodynamical simulations, to help understand the angular momentum content of galaxies in the local Universe. We investigate the relationship between thousands of galaxies' stellar and gas kinematics using both real and mock observations, to better understand the reliability of such simulations, and, how they can intuit their evolutionary histories. In this thesis, we investigate how the rotational direction of stars and gas can become decoupled (kinematic misalignment) and how this is related to the galaxy's morphology and the angular momentum content of the surrounding dark matter halo (Chapter 2). We also demonstrate the relationship between kinematic misalignment and stellar angular momentum, and how both are impacted by the role of feedback from supermassive black holes (Chapter 3), and, their large-scale environment. In particular, we investigate how the magnitude and direction of angular momentum in galaxies is modulated by their position within the cosmic web (Chapter 4), and, how kinematic misalignment is related to the assembly history of their dark matter halo (Chapter 5). Finally this thesis investigates the potential to recover the dynamics of dark matter within different large-scale environments (Chapter 6), motivating a novel application of the axisymmetric Jean's equations using whole galaxies as tracers. This work helps lay the foundation for using integral field spectroscopy and cosmological simulations, in tandem, as a powerful tool in building a holistic picture of galaxy evolution.

Star-forming galaxies can be transformed into passive systems through a multitude of mechanisms that quench star formation, such as the halting of cold gas accretion (known as starvation) and the rapid removal of gas in AGN-driven winds. However, it remains unclear which mechanism is the most significant, primary driver of the star-forming–passive bimodality. Leveraging on the statistical power of the Sloan Digital Sky Survey, we have investigated how galaxy quenching depends on both the internal properties of galaxies (i.e. stellar mass) and external factors (i.e. environment), how galaxy quenching has evolved across cosmic time and how quenching operates within galaxies. Building upon an innovative technique for assessing the relative impact of different quenching mechanisms through comparisons of the levels of chemical enrichment in star-forming, green valley and passive galaxies, we have analysed the chemical properties of tens of thousands of galaxies in the local Universe to unveil the primary quenching mechanisms in galaxies. We find that the significant difference in stellar metallicity between passive galaxies and their star-forming progenitors implies that for galaxies at all masses, quenching must have involved an extended phase of starvation. In order to best match the observed properties of local passive galaxies, some form of gas ejection has to be introduced in our models, with outflows becoming increasingly more important with decreasing stellar mass. Through an analysis of the local population of green valley galaxies, we find that quenching operates more slowly in the local Universe than at high redshift. By separating star-forming, green valley and passive galaxies, we further find that the environment leaves a much weaker imprint on the stellar populations of galaxies than was previously thought. Satellite galaxies are only marginally more metal-rich and older than central galaxies of the same stellar mass, with stellar metallicities that show only a weak dependence on halo mass, local overdensity and projected distance from their central. Finally, we find, using integral field spectroscopy from the SDSS-IV MaNGA galaxy survey, that passive galaxies are substantially more metal-rich than star-forming galaxies at all radii, with the stellar metallicity difference decreasing with increasing radial distance. Therefore, starvation is a primary driver of quenching at all radii in galaxies, playing a prominent role in quenching the central regions of galaxies, but playing an increasingly less important role in quenching their outskirts.

Galaxy evolution at radio wavelengths is often measured using luminosity functions which are commonly based on the luminosity (L) and redshift (z) of individual sources as well as the overall distribution for a sample. However, an important factor when K-correcting radio sources to their rest-frame luminosity is the spectral index (α). This is often assumed to be a constant value for the entire sample. In reality, there is a distributioninαwhich affects the rate at which sources drop below the flux limit of thesurvey. If not accounted for, the differing rates at which sources become unobservable can be mistaken as a genuine decline in source numbers and affect the evolution of the radio luminosity function (RLF). To tackle this, I estimate RLFs incorporating theα-distribution for both active galactic nuclei (AGN) and star forming galaxies (SFGs). Data from the Low-Frequency Array (LOFAR) and the Very Large Array (VLA) are used to formulate 150 MHz RLFs for a sample of AGN. MeerKAT and VLA data are used to measure and model the 1.4 GHz RLFs for a sample of SFGs. Markov Chain Monte Carlo sampling is used to find parameters to fit models based onρ(L,z) andρ(L,z,α) for comparison. The main findings of this work are that the accurate modelling of theα-distribution has a significant effect on not only the shape of the RLF,but the value of the evolution parameter k, parameterised as (1 +z)k in pure evolution and pure density evolution. This is true for both AGN and SFGs. The AGN RLF model has higher values of k when accounting for theα-distribution. Steep spectrum sources drop out of the flux limit of a survey earlier and therefore drive the RLF to evolve faster. The SFG RLF model has lower values of k when α is accounted for, since high values of k are found to compensate for the absence ofαinformation. Since the aim of RLFs is to measure the evolution of galaxies, it is imperative that the α-distribution be included to obtain accurate estimates of the strength of any evolution. Future work would aim to improve on this further through including an-other factor that affects the visibility of a source; the angular or projected linear size of the source. In this thesis, observations of the same field but using different antenna configurations have shown that high-resolution,long baseline imaging needs to be supplemented with short baseline observations to fully capture all scales of emission and all sources. Therefore, a radio telescope with an abundance of both short and long baselines is necessary. MeerKAT is such a telescope, as will be the SKA. Therefore, my work has set out the way forward for towards properly understanding the evolution of radio sources in the Universe.

The work in this thesis uses 38 orbits worth of Hubble Space Telescope (HST), Wide Field Camera 3 (WFC3) infrared F140W imaging and G141 grism data on 10 galaxy clusters at z~1 to study how the quenching of star formation in galaxies and galaxy size growth operates in different environments at this redshift. The unique capabilities of space-based slitless spectroscopy with the G141 grism allows for the construction of spatially resolved Hα maps, providing the possibility to directly observe environmental quenching at z~1 for the first time. This allows us to understand the detailed physics behind environmental quenching mechanisms and how they operate on galaxies at this high redshift. The quenching of star formation leads to the build-up of quenched (or 'quiescent') galaxies in the Universe. Observations have also shown that quiescent galaxies grow disproportionately more in size than stellar mass from high to low redshifts. Many studies have argued that minor mergers are responsible for this size growth. To test this hypothesis, it is possible to use the cluster environment as a laboratory. Cluster galaxies have high peculiar velocities, making mergers between them rare. Since minor mergers are expected to increase galaxy size more than they do stellar mass, the most direct way to test this is to measure the stellar mass-size relations in both the cluster and field environments at fixed redshift and compare them to see if there is a significant offset in size. If the predictions of minor mergers driving galaxy size growth are true, cluster galaxies should find themselves inhibited from size growth and will therefore be significantly smaller than field galaxies at fixed stellar mass. In Chapter 2 of this thesis, we do this experiment at z~1, finding that quiescent cluster galaxies are smaller than quiescent field galaxies at fixed stellar mass. This supports the case for minor mergers driving size growth in quiescent field galaxies. Nevertheless, the process whereby large star-forming galaxies quench and join the quiescent population at the large size end has also been suggested as an explanation for the size growth of quiescent galaxies. Using ancillary spectroscopy of our 10 clusters from the Gemini Cluster Astrophysics Spectroscopic Survey (GCLASS), we pick out 23 spectroscopically confirmed recently quenched galaxies in the clusters and study their position on the stellar mass-size relation in Chapter 3. We find that they follow a mass-size relation lying midway between the star-forming and quiescent relations. This result provides direct evidence showing galaxies which quench later are on average larger than the bulk of the quiescent galaxy population at fixed stellar mass and redshift. This work showed that at least in the cluster environment, recently quenched galaxies will induce a rise in the average size of quiescent galaxies with decreasing redshift. Finally, this thesis attempts to tackle one of the biggest unanswered questions in galaxy evolution: how does quenching operate in the high-redshift Universe? Surveys such as GASP and VESTIGE have already allowed us to build a comprehensive understanding of environmental quenching in the local Universe. Obtained using the WFC3 G141 grism, we use spatially resolved Hα maps of cluster and field galaxies at z~1 to directly observe where star formation is occurring in these galaxies and where it is not. In Chapter 4, we measure the stellar mass-size relations of z~1 star-forming cluster and field galaxies in F140W and Hα. The lack of a clear environmental quenching signature in this work hints at the rapidity of environmental quenching in the high-redshift Universe, and/or a complete change in the physics of environmental quenching.

The recent discovery of an 800 million solar mass black hole powering a quasar at a redshift corresponding to 690 million years after the Big Bang is the latest in a growing list of observations of super-massive black holes (SMBHs) that were most likely seeded with masses larger than those expected from the remnants of the first generation of stars. This thesis investigates the consequences of the seeding of SMBHs by massive black holes on galaxy evolution through a combination of analytic modelling techniques. Firstly, I analytically model the growth of gravitational instabilities in an isolated proto-galaxy disc as it progresses into a fully-formed galaxy in the presence of a massive seed black hole formed directly through isothermal collapse. The model shows for the first time how the gravitational effects of a seed black hole lead to an increase in the stability of the disc and an increase in the star formation timescale in the region of the disc close to the black hole. This gravitational imprint of the black hole on the galactic disc has the effect of suppressing star formation. To investigate if this has a lasting effect on the properties of seed hosting galaxies, I evolve the disc galaxy model from the epoch of seed formation down to z ~ 6. I show how star formation in seed hosting galaxies is further regulated by a combination of gravitational stability and the accretion of gas onto the black hole, leading to a scenario where the resulting ratio of black hole to stellar mass at z = 6 is significantly higher than observed in the local universe. I also investigate how the growth of massive seed black holes is regulated by the mass and momentum transport in the disc. The inward accretion of gas towards the central massive black hole and therefore the accretion of gas onto the black hole itself is a function of the stability of the disc. The stabilising effect of the black hole therefore has the potential to regulate the inflow of gas, depending on the relative masses of the galaxy disc and black hole. I find that even in the regime where the inflow rate is not affected by the presence of the black hole, viscosity driven accretion is too inefficient for even massive seeds to grow into a SMBHs by z ~ 6. This indicates the isolated growth of SMBHs is not possible. Indeed, merger events or other processes which are efficient at dissipating angular momentum are required to provide the necessary rapid accretion of gas for SMBHs to form. Finally, I study the dynamical heating of a dark matter halo through the accretion of massive black hole systems. Modelled as both a black hole embedded in its own subhalo and as a naked black hole, the infall of the black hole system acts as a perturber to the density of the central halo, converting potential energy to heat the gas of the central halo through dynamical friction. The timescale over which this infall occurs decreases with a larger perturber mass relative to the central halo mass. The total energy released through black hole accretion during the period of infall is strongly dependent on the black hole growth model. Generally, the total energy from black hole growth exceeds the total energy from dynamical friction. However, the energy released through dynamical friction reaches a maximum when the perturber's proximity to the centre of the central halo is minimised, generally after black hole accretion has ceased. There is therefore a period of time where dynamical friction is the primary source of heating within a halo, potentially contributing to the luminosities of some distant quasars and leading to over-estimates in inferred black hole masses.

The formation and evolution of galaxies is governed by a set of complex non-linear physical processes. When we observe a galaxy at a particular epoch, we see a unique spatial distribution of stars, gas and dust, and can use the light emitted by these components to infer the chemical composition and dynamics of the galaxy. The spatial distribution of the different components, as well as the galaxy chemistry and dynamics, is shaped by the history of both the internal and external physical processes involving the galaxy until the time of observation. Although no two galaxies appear the same, the study of galaxy evolution is an attempt to understand generally the physical processes which lead to the observed distribution of galaxy properties at any stage across the history of the Universe. Many of these processes are still poorly understood, particularly in terms of the timescales over which they operate and their importance in the energetics of the galaxy. Much progress has been made in this area in both the local and distant Universe over recent years, thanks in particular to multi-object integral-field spectrographs, which have allowed for the spatial mapping of representative samples of the galaxy population. This thesis presents studies of the spatially resolved dynamical and chemical properties of high-redshift star-forming galaxy samples, using integral-field spectroscopic observations with the K-band Multi-Object Spectrograph (KMOS). In Chapter 2 I describe the data reduction pipeline developed to process these observations. Specifically, I have added processing steps which extend this pipeline beyond the standard recipes and describe these in the chapter. In Chapter 3, using a sample of 77 star-forming galaxies from the KMOS Deep Survey (KDS) at a median redshift of z ≃ 3:5, I demonstrate that the intrinsic, beam-smearing corrected velocity dispersions are ubiquitously high, with a sample median value of 70.8kms-1. At this redshift, the KDS sample is the largest from which these observations have been made and the measurements indicate that the trend of increasing intrinsic velocity dispersions continues out to at least z ≃ 3:5. In Chapter 4, by compiling 16 high-redshift comparison samples from the literature, I study the evolution of the stellar mass Tully-Fisher relation, demonstrating clearly that recent literature discrepancies can be explained by differing sample selection criteria. By also examining the rotation-velocity fields of the KDS galaxies, I discuss the possibility that a significant portion of gravitational support is provided by random motions, as evidenced by the redshift decline of the ratio of rotation velocity to velocity dispersion. This leads to the formulation of a 'total velocity' containing both velocity dispersion and rotation velocity terms. Combining the intrinsic velocity dispersion values with the rotation velocities of the galaxies is necessary to trace the galaxy potential wells at intermediate and high redshift. When this is done, the evolution of the normalisation of the total-velocity versus stellar-mass relation is consistent with a steady decline over cosmic time. Finally, using multi-band KMOS observations from the KMOS LEnsed galaxies Velocity and Emission line Review (KLEVER) survey, I explore the spatial distribution of emission-line ratios across individual galaxies at z ≃ 2:3, finding significant variation in the dust content and gas excitation conditions between galaxy cores and outskirts. The majority of KLEVER galaxies are observed to have negative Balmer decrement gradients (centrally concentrated dust distributions), with more-negative gradients belonging to the galaxies with higher stellar mass, lower Hα velocity dispersions and lower Hα luminosities. Similarly, the dust-corrected ratio of the [O iii]λλ4960; 5007/[O ii]λλ3727; 3729 emission lines (which may be used as a proxy for metallicity) for the majority of KLEVER galaxies has a radial profile with a positive gradient (i.e. higher metallicity cores), with more-positive gradients also correlating with higher stellar mass, lower Hα velocity dispersions and lower Hα luminosities. This work is still preliminary and requires further work to strengthen and build on the conclusions. The fundamental objective of the work presented throughout this thesis is to understand the spatially-resolved dynamical and chemical structure of high-redshift star-forming galaxies and to draw conclusions regarding how they evolve into the star-forming galaxies we observe in the local Universe.

The work in this thesis concerns the host galaxies of a class of luminous, yet heavily-obscured, quasars at z$\sim$2 - a peak epoch of both star formation and black hole accretion. Here, we seek to characterise the star-forming properties of these obscured quasars to improve our understanding of galaxy-quasar coevolution. A key issue facing host galaxy studies among populations of the most luminous quasars is being able to disentangle the galaxy emission from that of the quasar. With combined observations from the Dark Energy Survey (DES), the VISTA Hemisphere Survey (VHS) and the UKIDSS Large Area Survey (ULAS), we exploit the quasar dust extinction in our sample to demonstrate that the quasar and galaxy emission can be separated via SED-fitting in these systems. By isolating the galaxy emission in this way, we estimate instantaneous SFRs for the galaxies in our sample, based on the restframe UV emission. In general, we find obscured quasars to reside in prodigiously star forming hosts with 25 $\lesssim$ SFR$_{\rm{UV}}$ $\lesssim$ 365 M$_{\rm{\odot}}$yr$^{-1}$. Furthermore, we show that the most luminous quasars reside in the most actively star-forming galaxies, potentially indicating the same gas supply is fuelling both star formation and accretion on to the black hole. Having isolated the galaxy emission via SED-fitting, we test our ability to model the restframe-UV emission of obscured z$\sim$2 quasar hosts in 2D. Until now, morphological studies of luminous quasar hosts have typically been limited to low redshifts or relied on space-based imaging. By making use of a multi-band modelling code however, we demonstrate that it is possible to accurately infer several galaxy properties (i.e. the position of the galaxy in the image, (X,Y), its radius, R$_{\rm{eff}}$, axis ratio, q$_{\rm{GAL}}$, angle of orientation, $\theta$, and S\'{e}rsic index, $n$), based on current ground-based imaging, accross the full range of galaxy and quasar luminosities considered in our sample. This potentially opens the door to future ground-based morphological studies of obscured quasars at high redshift. At sub-mm wavelengths, thermal emission from cold dust peaks, meaning these wavelengths can be used to probe the dust heating by star formation, effectively giving a measure of the obscured star formation in the galaxy. Using targeted observations from SCUBA-2, we trace the 850$\mu$m emission in a sample of obscured quasars, finding evidence for prodigious star formation $ > $ 2400 M$_{\rm{\odot}}$yr$^{-1}$ in three of the 19 quasars in our sample. The detection rate of our obscured quasar sample is found to be consistent with that of both more heavily-obscured Hot-DOGs and UV-luminous quasars, once the samples have been matched in luminosity and redshift. Furthermore, we find evidence that several of the obscured quasars lie in overdense regions of the sky ($\sim$ 3 times denser than sub-mm blank fields).

There is a strong consensus within the scientific literature that the most powerful radio galaxies are the result of gas-rich, major mergers causing large amounts of material to fall on to the black hole at the centre of the resulting galaxy, thus producing an immensely powerful radio jet. However, such galaxies are extremely rare and are not representative of the general radio galaxy population. Most radio galaxies have low power, and their basic properties and origins are poorly constrained. One of the most popular suggestions is that they are bona-fide detections of jet-mode active galactic nuclei (AGN), a class of AGN thought to maintain the dearth of star formation in early-type galaxies (ETGs), after most of the fuel for star formation has been removed by an earlier event. If true, then all ETGs must regularly go through such an active phase, and low-powered radio galaxies should be much the same as their radio-quiet (quiescent phase) ETG counterparts. To test this hypothesis, a complete sample of 11 nearby low-powered radio galaxies was constructed and observed with a suite of instruments. We focus here on the spatially-resolved stellar kinematics, stellar populations, and ionized gas distribution, kinematics and ionization derived from integral-field spectroscopic (IFS) observations with the Visible Multi-object Spectrograph (VIMOS) and archival data from the Multi-unit Spectroscopic Explorer (MUSE), both on the Very Large Telescope (VLT). We compare the characteristics and properties (accessible with V-band IFS data) of our sample of low-power radio galaxies to those of ordinary (i.e. optically-selected) ETGs from the Atlas3D and MASSIVE IFS surveys. For the stellar component of our sample galaxies, we use the kinematic maps to identify regular/non-regular rotators and kinematic substructures. In our sample 4 galaxies are regular rotators and two (with a tentative third) galaxies were found to contain kinematically decoupled cores (KDCs). We use the lambdaR specific angular momentum parameter from Atlas3D to classify the galaxies according to the fast/slow rotator classification scheme. We found a similar fraction (45+/-13%) of slow rotators to the combined Atlas3D and MASSIVE samples, corrected for mass distribution. We also find that fast rotators tend to have aligned kinematic and photometric position angles, while the slow rotators can have any angle between the two position angles. The best-fitting stellar populations show our sample to be typical massive ETGs: i.e. mostly old, metal rich and alpha-element enhanced. We found and measure the radial stellar population gradients and found averages of Deltalog age = 0.014 ± 0.007 dex-1 and Delta[Fe/H] = -0.03±0.01 dex arcsec-1. The KDCs found previously were observed to be large and contain old stellar populations and are the result of galaxy mergers. Some literature suggests that if the AGN is fuelled by accreted cold gas then it might be expected to form stars within the accretion disc. However we see no evidence of a very young stellar population right at the centre of our sample galaxies. For the ionized gas components of our sample galaxies, the estimated gas masses were found to be in the range of 104 - 106 Modot, which is the upper end of the range expected from optically-selected ETGs. This was the only suggestion we find that our sample galaxies may be intrinsically different than optically-selected ETGs. We detected spatially extended gas in 4 of our sample, with a range of kinematics. Two galaxies had ionized gas kinematics misaligned to that of the stars, suggesting an external origin to the gas, while the kinematics of one was aligned with that of its stars (consistent with an internal origin). The final galaxy was unsettled and thus not clear. Using the classic Baldwin-Phillips-Terlevich (BPT) diagnostic plots, as well as similar alternatives, for galaxies with observations outside of the wavelength range required for the BPT plots, we find the dominant ionization source for each galaxy. We find that 9 of our sample galaxies are low-ionized nuclear emission region galaxies (LINERs; 5 of which can be attributed to the radiation field from the AGN), 1 is a Seyfert II and 1 a passive (line-less) galaxy. All of the properties found are consistent with that of optically selected ETGs with a similar mass distribution. We thus find no conclusive difference between the stellar and ionized gas properties all of these ETGs except for a tentative suggestion of slightly higher ionized gas masses in our radio galaxies. If confirmed, the latter may be gas built up during the quiescent phase of ETGs, ultimately triggering the active (radio) phase itself then re-removing such gas from the galaxy. Some of the sample galaxies have clear evidence of merger events (e.g. large KDCs), but others have a complete lack of evidence of a merger, suggesting that radio galaxies can form without the requirement of a merger event. Indeed, it is well known that NGC 612 harbours a large extended gas disc with kinematics that are consistent with an internal origin of the gas. As such, in rare cases, it is possible that radio galaxies can be fuelled through entirely secular processes.

Bars are common in disc galaxies along with many associated structures such as disc-like bulges, boxy/peanut bulges, rings, etc. They are a sign of maturity of disc galaxies and can play an important role in their evolution. In this thesis, I investigate the specific role bars play in quenching the star formation in, and shaping of their host galaxies. In order to test how bars affect their host galaxies, I study the discs, bars and bulges of what is currently the largest sample of barred galaxies (~3,500), selected with visual morphologies from the Galaxy Zoo project. I perform multi-wavelength and multi-component photometric decomposition, with the novel GALFITM software. With the detailed structural analysis I obtain physical quantities such as the bar- and bulge-to-total luminosity ratios, effective radii, Sérsic indices and colours of the individual components. I find a clear difference in the colours of the components, the discs being bluer than the bars and bulges. An overwhelming fraction of bulge components have Sérsic indices consistent with being disc-like bulges. I compare the barred galaxies with a mass- and environment-matched volume-limited sample of unbarred galaxies, finding that the discs of unbarred galaxies are bluer compared to the discs of barred galaxies, while there is only a small difference in the colours of the bulges. I suggest that this is evidence for secular evolution via bars that leads to the build-up of disc-like bulges and to the quenching of star formation in the galaxy discs. I identify a subsample of unbarred galaxies that are better fitted with an additional component, identified as an inner lens/oval. I find that their structural properties are similar to barred galaxies, and speculate that lenses might be former bars. Using the decompositions, I identify a sample of 271 late-type galaxies with curious bars that are off-centre from the disc. I measure offsets up to 2.5 kpc between the photometric centres of the stellar disc and stellar bar, which are in good agreement with predictions from simulations of dwarf-dwarf tidal interactions. The median mass of these galaxies is 109.6 M⊙, and they are similar to the Large Magellanic Cloud, which also has an offset bar. Very few high mass galaxies with significant bulges show offsets, thus I suggest that the self-gravity of a significant bulge prevents the disc and bar from getting displaced with respect to each other. I conduct a search for companions to test the hypothesis of tidal interactions, but find that a similar fraction of galaxies with offset bars have companions within 100 kpc as galaxies with centred bars. Since many of these galaxies appear isolated, interactions might not be the only way to produce an offset bar. One suggested alternative is that the dark matter haloes surrounding the galaxies are lopsided, which distorts the potential, and imprints the lopsidedness and offsets onto the galaxy discs. I investigate the asymmetries in the kinematics of a subsample of such galaxies using data from the MaNGA survey, and find that the perturbations in the haloes are ~ 6% for both galaxies with off-centre and centred bars. I also measure the amplitude of non-circular motions in the outer discs due to an oval potential and find only minor departures from circularity, suggesting that the dark matter haloes are consistent with being spherical (axis ratio q ≳ 0.96). Therefore, the lopsidedness of the dark matter haloes cannot be the origin of the offsets. Either small companions are missed due to the incompleteness of the Sloan Digital Sky Survey spectroscopic survey, or interactions with dark matter satellites might explain the offsets. Modeling the kinematics of these galaxies, I find that the Hα gas rotation is centred closer to the centre of the bar than the centre of stellar rotation, suggesting that, in general, the bars are located closer to the dynamical centres of these galaxies than the discs. This implies that the discs are offset in these galaxies, not the bars. If offsets are characteristic of low mass galaxies only, high mass galaxies show vertically extended bars, known as boxy/peanut bulges. I investigate, for the first time, the formation and evolution of these structures associated to bars, from z≈0 to z=1. I compare two samples of moderately inclined galaxies with masses M* > 1010 M⊙, imaged by the Sloan Digital Sky Survey and the Hubble Space Telescope. Using a novel technique to classify bar isophotes, and based on the visual inspection of three expert astronomers, I find an evolving fraction of galaxies having boxy/peanut bulges from 30% at z≈0 to ~ 0% at z=1, and a strong correlation with stellar mass. I find 26 galaxies (15 at higher redshifts) in the phase of bar buckling, the mechanism proposed to form boxy/peanut bulges. The peak redshift of buckling is z≈0.75, where the bar buckling fraction is 4 times higher than in the local Universe. My observations suggest that many, if not all, of the boxy/peanut bulges are formed via buckling, ~ 2 Gyr after bar formation, with the buckling phase lasting for approximately 0.8 Gyr. I discuss my findings in the context of the evolution of barred galaxies and propose ideas for future work - applying similar decomposition techniques to higher redshift, and better resolution datasets, using integral field spectroscopic data to study the stellar populations of barred galaxies in greater detail, as well as a novel project to identify large nuclear discs in galaxies.

Supermassive black holes (BHs) and their host-galaxies are thought to evolve in tandem, with the energy output from the rapidly-accreting BH regulating star formation and the growth of the BH itself. The goal of better understanding this process has led to much work focussing on the properties of quasars at high redshifts, $z\gtrsim 2$, when cosmic star formation and BH accretion both peaked. At these redshifts, however, ground-based statistical studies of the quasar population generally have no access to the rest-frame optical spectral region, which is needed to measure H$\beta$-based BH masses and narrow line region outflow properties. The cornerstone of this thesis has been a new near-infrared spectroscopic catalogue providing rest-frame optical data on 434 luminous quasars at redshifts $1.5 \lesssim z \lesssim 4$. At high redshift, $z \gtrsim 2$, quasar BH masses are derived using the velocity-width of the CIV broad emission-line, based on the assumption that the observed velocity-widths arise from virial-induced motions. However, CIV exhibits significant asymmetric structure which suggests that the associated gas is not tracing virial motions. By combining near-infrared spectroscopic data (covering the hydrogen Balmer lines) with optical spectroscopy from SDSS (covering CIV), we have quantified the bias in CIV BH masses as a function of the CIV blueshift. CIV BH masses are shown to be over-estimated by almost an order of magnitude at the most extreme blueshifts. Using the monotonically increasing relationship between the CIV blueshift and the mass ratio BH(CIV)/BH(H$\alpha$) we derive an empirical correction to all CIV BH-masses. The correction depends only on the CIV line properties and therefore enables the derivation of un-biased virial BH mass estimates for the majority of high-luminosity, high-redshift, spectroscopically confirmed quasars. Quasars driving powerful outflows over galactic scales is a central tenet of galaxy evolution models involving 'quasar feedback' and significant resources have been devoted to searching for observational evidence of this phenomenon. We have used [OIII] emission to probe ionised gas extended over kilo-parsec scales in luminous $z\gtrsim2$ quasars. Broad [OIII] velocity-widths and asymmetric structure indicate that strong outflows are prevalent in this population. We estimate the kinetic power of the outflows to be up to a few percent of the quasar bolometric luminosity, which is similar to the efficiencies required in recent quasar-feedback models. [OIII] emission is very weak in quasars with large CIV blueshifts, suggesting that quasar-driven winds are capable of sweeping away gas extended over kilo-parsec scales in the host galaxies. Using data from a number of recent wide-field photometric surveys, we have built a parametric SED model that is able to reproduce the median optical to infrared colours of tens of thousands of AGN at redshifts $1 < z < 3$. In individual objects, we find significant variation in the near-infrared SED, which is dominated by emission from hot dust. We find that the hot dust abundance is strongly correlated with the strength of outflows in the quasar broad line region, suggesting that the hot dust may be in a wind emerging from the outer edges of the accretion disc.

In this thesis, I develop and combine strong lensing and dynamical probes of the mass of early-type galaxies (ETGs) in order to improve our understanding of their dark and luminous mass structure and evolution. Firstly, I demonstrate that the dark matter halo of our nearest brightest cluster galaxy (BCG), M87, is centrally cored relative to the predictions of dark-matter-only models, and suggest an interpretation of this result in terms of dynamical heating due to the infall of satellite galaxies. Conversely, I find that the haloes of a sample of 12 field ETGs are strongly cusped, consistent with adiabatic contraction models due to the initial infall of gas. I suggest an explanation for these differences in which the increased rate of merging and accretion experienced by ETGs in dense environments leads to increased amounts of halo heating and expansion, such that the signature of the halo's initial contraction is erased in BCGs but retained in more isolated systems. Secondly, I find evidence that the stellar-mass-to-light ratio declines with increasing radius in both field and cluster ETGs. With M87, I show that the strength of this gradient cannot be explained by trends in stellar metallicity or age if the stellar initial mass function (IMF) is spatially uniform, but that an IMF which becomes increasing bottom-heavy towards the galaxy centre can fully reproduce the inference on the stellar mass. Finally, I use the sizes, stellar masses and luminous structures of two samples of massive ETGs at redshift z ~ 0.6 to set constraints on the mechanisms of ETG growth. I find that ETGs in dense cluster environments already lie on the local size-mass relation at this redshift, contrary to their isolated counterparts, and suggest that this may be evidence for their accelerated growth at early times due to the higher incidence of merger events in clusters. I also show that massive compact ETGs at this redshift are composed of a compact, red, spheroidal core surrounded by a more extended, diffuse, bluer envelope, which may be a structural imprint of their ongoing inside-out growth. Overall, the studies presented in this thesis suggest a coherent scenario for ETG evolution which is dominated by hierarchical processes.

Within the currently well-established ΛCDM cosmological framework we still lack a satisfactory un- derstanding of the processes that trigger, regulate and eventually quench star formation on galactic scales. Gas flows (including inflows from the cosmic web and supernovae-driven outflows) are con- sidered to act as self-regulatory mechanisms, generating the scaling relations between stellar mass, star formation rate and metallicity observed in the local Universe by large spectroscopic surveys. These surveys, however, have so far been limited by the availability of only one spectrum per galaxy. The aim of this dissertation is to expand the study of star formation and chemical abundances to resolved scales within galaxies by using integral field spectroscopy (IFS) data, mostly from the ongoing SDSS- IV MaNGA survey. In the first part of this thesis I demonstrate the ubiquitous presence of extended low ionisation emission-line regions (LIERs) in both late- and early-type galaxies. By studying the Hα equivalent width and diagnostic line ratios radial profiles, together with tracers of the underlying stellar popula- tion, I show that LIERs are not due to a central point source but to hot evolved (post-asymptotic giant branch) stars. In light of this, I suggest a new classification scheme for galaxies based on their line emission. By analysing the colours, star formation rates, morphologies, gas and stellar kinematics and environmental properties of galaxies with substantial LIER emission, I identify two distinct popula- tions. Galaxies where the central regions are LIER-like, but show star formation at larger radii are late types in which star formation is slowly quenched inside-out. This transformation is associated with massive bulges. Galaxies dominated by LIER emission at all radii, on the other hand, are red-sequence galaxies harbouring a residual cold gas component, acquired mostly via external accretion. Quiescent galaxies devoid of line emission reside in denser environments, which suggests environmental effects as a likely cause for the existence of line-less galaxies on the red sequence. In the second part of this dissertation I focus on the study of resolved chemical abundances by characterising the gas phase oxygen and nitrogen abundance gradients in a large sample of star forming galaxies. I analyse the deviations from an exponential profile at small and large radii and the dependence of the gradients on stellar mass. These findings are interpreted in the context of the inside-out paradigm of disc growth. I then demonstrate the necessity of gas flows, which are responsible for the observed flattening of the metallicity and N/O ratio gradients at large radii. Finally, I present a case study based on one nearby galaxy (NGC 628), in which I combine IFS and cold gas data to derive a spatially resolved metal budget and estimate the mass of metals lost by the galaxy throughout its life- time. By using simple physically-motivated models of chemical evolution I infer the average outflow loading factor to be of order unity.

Environment is known to have a significant impact on the evolution of galaxies. This is most evident in the local Universe, where the oldest and most massive galaxies are found at the of massive galaxy clusters. Current theory predicts that galaxies will form earlier and evolve more rapidly in the densest regions of the Universe. What is not clear is how rapidly the of environment start to have an impact on galaxies, at what stage can we detect physical differences between galaxies in dense regions and those in the field? By the time galaxies are assembled in virialised clusters the effects are clear, but at higher redshift (z ≳ 2), in the unvirialised progenitors of clusters (protoclusters) the effects are harder to detect. In this thesis I study the impact of environment in a z =3.1 protocluster in the SSA22 field. I consider the fraction of mergers in the protocluster, comparing it to the fraction of mergers in field at a similar redshift. My classification is based on the morphology of Lyman break (LBGs), using HST ACS/F814W imaging, which probes the rest frame UV. I find a marginal enhancement of the merger fraction, 48±10 per cent for LBGs in the protocluster compared 30±6 per cent in the field, suggesting that galaxy-galaxy mergers are one of the key driving accelerated star formation and AGN growth in protocluster environments. Having considered the fraction of mergers in the protocluster I then turn my attention to the physical properties of LBGs. I use multiwavelength data and spectral energy distribution fitting to determine the mass of LBGs in the protocluster and in the field. I find no statistical evidence for an enhancement of mass in the protocluster, suggesting that the protocluster environment has not impacted the average mass of LBGs at this redshift. It is possible that the protocluster LBG population may become more massive than LBGs in the field at lower redshift, or the galaxies may cease to be detectable by the Lyman break method before a mass difference between the protocluster galaxies and field is observable. Finally I consider the Lyman-α blobs (LABs) within the protocluster. These are large (~10- 100kpc) scale regions of diffuse Lyman-α emission, thought to be associated with overdense regions. 35 LABs have been detected in the SSA22 protocluster, indicating the presence of large clouds of gas in the circumgalactic medium. A debate has arisen regarding the powering mechanism of the LABs, particularly between star forming processes (e.g. Lyman-α escaping from a star forming galaxy or photoionizing radiation escaping from a star forming galaxy or active galactic nuclei) and a cold accretion model. The latter involves gas gravitationally cooling as it falls into the centre of a dark matter halo to feed a central galaxy. Some of this energy heats the cold gas, which then emits Lyman-α as it cools. The cold gas accretion theory gained popularity because some LABs appear not to contain a luminous galaxy or AGN which could explain the observed emission. One suggestion is that the central galaxy could be hidden by dust and that this could explain the lack of a detection in UV or optical. I therefore use SCUBA2 850μm imaging to search for submm sources (dusty star forming galaxies) in the LABs. I detect submm sources in only two of the LABs at 3.5δ, however, stacking all the LABs gives an average flux density of S850 = 0.6±0.2mJy. This suggests that on average the LABs do contain a submm source which could be a dusty galaxy. However, stacking the LABs by size indicates that only the largest third (area ≳ 1800kpc²) have a mean detection, at 4.5δ, with S850 = 1.4±0.3mJy, suggesting that different mechanisms may dominate the larger and smaller LAB populations. I explore two possible mechanisms for powering the LABs, cold accretion and central star forming galaxies. I find that central star formation is more likely to be the dominant source of emission, with cold accretion playing a secondary role.

In this thesis we explored the use of nuclear stellar discs as tracers of the merging history of early-type galaxies. These small structures, just a few tens to a few hundreds of parsecs across, are a common but poorly studied feature of early-type galaxies. They are formed during or shortly after merging events due to the infall of gas, which settles in a disc and leads to the formation of new stars. Initial simulations showed that they should not survive a following major merger and could, therefore, be used to trace the epoch when their host galaxies experienced their last major merger event. We produced the first census of nuclear discs and established that their incidence is 20%, fairly independent of the host-galaxy mass or galactic environment. Furthermore, we have more than doubled the sample of nuclear discs with known photometric properties, finding that they give a hint of possessing different characteristics from those of large, galactic discs. Using these nuclear discs as clocks for the assembly history of galaxies requires dating their stellar populations. By combining the use of integral-field spectroscopy with the a priori knowledge of the relative bulge- and disc-light contribution to the observed spectra, as determined by a photometric disc-bulge decomposition, we have shown that it is possible to reduce the degeneracies that affect the study of two superimposed populations and thus that the age of stellar discs can be measured more precisely. To illustrate our method, we present VLT-VIMOS data for NGC 4458, a low-mass slowly rotating early-type galaxy with a disc that we found to be at least 5-6 Gyr old. The presence of such an old central disc in such a small, slowly-rotating and, mostly likely, round galaxy is particularly puzzling and presents a challenge to existing models. Disc fragility is central to our studies and we have expanded the limited initial simulations to study it in more detail. By means of N-body simulations, we have reproduced the final stages of a galaxy encounter by exposing a nuclear disc rotating in the gravitational potential of its host bulge and central supermassive black hole to the impact of a secondary massive black hole. We explored not only major mergers (1:1 mass ratio), but also large minor mergers (1:5 and 1:10), across a variety of collision angles, and assessed the survival of the disc, as perceived by current observational limits, both for photometry and spectroscopy. As expected, the discs do not survive a major merger whereas it is in general possible to detect their presence after a 1:5 or 1:10 encounter, in particular when looking at kinematic signatures with spectroscopy. This thesis has demonstrated that nuclear discs constitute both a common and accurate tool for constraining the assembling history of nearby early-type galaxies. The advent of more sensitive integral-field spectrographs, such as MUSE, will make measuring the stellar age of nuclear discs not only more precise, but also more economical in terms of telescope time. This will allow embarking on a more systematic age dating campaign for nuclear stellar discs across a wider range of type, mass and galactic environments for their host galaxies. Combining such a census with a larger set of numerical simulations aimed at calibrating better the range of merger event that would erase any photometric or kinematic signature of a nuclear disc, should finally allow us to put firm constraints on the merging history of early-type galaxies.

In this thesis we use the Tully-Fisher relation (TFR), the correlation between a galaxy's luminosity and its rotation velocity, to probe the luminous and dark matter in galaxies over the last ≈ 8 Gyr. First, we use samples of galaxies spatially resolved in Hα emission with integral field unit observations from the K-band Multi-Object Spectrograph (KMOS) Redshift One Spectroscopic Survey (KROSS) at z ≈ 1 and the Sydney-Australian-Astronomical-Observatory Multi- object Integral-Field Spectrograph (SAMI) Galaxy Survey at z ≈ 0. We match the data quality, analysis methods and sample selection between the two surveys to conduct a direct comparison of the absolute K-band magnitude (MK) and stellar mass (M*) TFRs at z ≈ 1 and z ≈ 0, free of any difference in biases between them. We measure no evolution of the MK TFR zero-point for star- forming disk-like galaxies since z ≈ 1, but an increase by 0.2 ± 0.2 dex of the M* TFR zero-point for the same galaxies over the same period. This implies the total mass-to-stellar mass ratio of those galaxies has decreased by a factor of ≈ 0.4 since z ≈ 1 at fixed rotation velocity, whilst their K-band stellar mass-to- light ratio has increased by a factor of ≈ 1.6. Moderate rates of star formation in galaxies and continued gas accretion since z ≈ 1 can explain these changes. Second, we take a step toward an independent measure of the TFR evolution over the same period using carbon monoxide (CO) emission from galaxies as an alternative kinematic tracer. We present the M* and Wide-Field Infrared Survey Explorer absolute Band 1 magnitude (MW1) TFRs for galaxies from the CO Legacy Database for the Galex Arecibo SDSS Survey (COLD GASS) as z ≈ 0 benchmarks that are pre-requisites to extend the CO TFR to z &gsim; 1. We find no significant offsets between the COLD GASS TFR zero-points and those of similar z ≈ 0 studies. The slope of the M* COLD GASS TFR agrees with those of similar z ≈ 0 studies, but the MW1 TFR slope is slightly shallower than previous studies at a similar redshift. We attribute this to the fact that the COLD GASS sample comprises galaxies of various (late-type) morphologies. Nevertheless, our work provides a robust reference point with which to compare future CO TFR studies.

In this thesis I investigate galaxy evolution by measuring the luminosity functions of galaxies across a wide range in redshift. I measure the abundances of high redshift galaxies in deep HST imaging of the GOODS-North field from the CANDELS survey. I follow this evolution to lower redshift by measuring the luminosity functions of galaxies in ground-based imaging of the XMM-LSS field from the VIDEO survey with optical data from the CFHTLS. First, at high-redshift, I identify 22 candidate z ≈ 7 and 6 candidate z ≈ 8 − 9 galaxies. By comparing the number of candidate galaxies with those found in the GOODS-South field, I determine that cosmic variance is not the dominant source of uncertainty on the number counts. I constrain the Schechter parameters for the UV luminosity function at z ≈ 7 and z ≈ 8 − 9, finding evidence for evolution in the number density of high redshift galaxies. Next, I present the Ks-band luminosity functions in the 1 degree2 and 4.5 degree2 overlaps between the VIDEO-XMM field and the CFHTLS-D1 and CFHTLS-W1 fields. I measure the luminosity functions with the 1/Vmax method over the range 0.2 &LT; z &LT; 3 in VIDEO-CFHTLS-D1, and over the range 0.2 &LT; z &LT; 1.5 in the shallower VIDEO-CFHTLS-W1 field. I find the evolution of these luminosity functions is best described by luminosity dependent density evolution, where the characteristic magnitude has dimmed at a constant rate since z = 3, while the density has increased since z = 3, first rapidly from z = 3 to z ≈ 1.5 and then more slowly from z ≈ 1.5 to z = 0.2. I measure a significant upturn at the faint end of the luminosity function at low redshift. Finally, I compare the VIDEO-CFHTLS-D1 and VIDEO-CFHTLS-W1 luminosity functions with predicted K-band luminosity functions from the Horizon-AGN simulation. I find both an over-prediction in the numbers of faint galaxies and an under-prediction in the numbers of bright galaxies, implying that the feedback from supernovae is insufficient while the feedback from AGN is over-sufficient.

In this thesis, I present the results of a new search for, and study of, luminous galaxies in the first billion years of cosmic time. This work is primarily based on a new selection of bright (L≫L*) Lyman-break galaxies (LBGs) at z ≅6 and z≅7 in the UltraVISTA first and second data releases (DR1, DR2) and the UKIDSS (UKIRT Infrared Deep Survey) UDS DR10 (Ultra Deep Survey). The UltraVISTA survey provides deep Y, J,H andKs near-imaging over 1.5 deg² of the Cosmic Evolution Survey (COSMOS) field and the UKIDSS UDS provides J,H and K band data overlapping with the Subaru XMM-Newton Deep Survey (SXDS), with both fields also containing deep optical and mid-infrared imaging essential for the clean detection of z > 5 galaxies. The fields combined provide an unprecedented 1.65 deg² of deep multiwavelength data with which to securely select LBGs using a photometric redshift fitting technique, which can additionally remove probable low-redshift galaxy interlopers and galactic dwarf stars that can contaminate ground-based samples. At z ≅7, the DR1 of the UltraVISTA survey was used to select a sample of ten high-redshift galaxy candidates, which extended to a 5σ limiting magnitude of Y + J ~ 25 (AB magnitude, 2-arcsec diameter circular aperture) over 1 deg². A stack of the four most robust objects from the sample indicated that they were massive (M*≅5 × 109M ʘ), had blue rest-frame UV slopes (β ≅−2.0±0.2) and were highly star-forming (SFR ≅25–50Mʘ yr−1) when compared to previous, fainter, samples of galaxies at z = 7. The number counts of z≅7 galaxies selected within the UltraVISTA DR1 survey was higher than that expected from extrapolations of the rest-frame UltraViolet (UV) luminosity function (LF) from fainter data, a result that was strongly confirmed with an improved search for z ≅7 galaxies using the UltraVISTA DR2 imaging and the UDS field. A total of 34 galaxies at 6.5 < z < 7.5 were found in the combined fields, which included the previously identified robust galaxies from the DR1 imaging. This expanded sample allowed the first determination of the rest-frame UV LF in the range −23.0 < MUV < −21.5 at z ≅7, and the results reveal a power-law decline to bright magnitudes in contrast to the commonly assumed exponentially declining Schechter function extrapolated from fainter data. The excess of galaxies observed at bright magnitudes cannot be accounted for by gravitational lensing or by significant contamination of the sample by Active Galactic Nuclei (AGN) . The observed LF is well described by a double power law, which at the bright end follows the form of the underlying dark matter halo mass function, suggesting that the physical mechanism that inhibits star formation activity in massive galaxies (e.g. AGN feedback or some other form of ‘mass quenching’) has yet become efficient at z ≅7. The deeper imaging data confirm that the z ≅7 LBGs show blue rest-frame UV slopes (median β = −2.0) and are massive (up to M*≅1010M ʘ). Furthermore, an analysis of the ground-based imaging shows that the majority are resolved consistent with larger sizes (r1/2 ≅1–1.5 kpc) than displayed by less massive galaxies. Finally, a new search for z ≅6 galaxies within the UltraVISTA and UDS datasets was undertaken, resulting in a sample of 266 LBGs (−22.7 < MUV < −20.5) galaxies with which to investigate the rest-frame UV LF. The potential contamination by galactic brown dwarfs was investigated quantitatively using a simple model of the Galaxy, showing that the expected contamination rate of the sample was < 3 per cent, and that the stars can be effectively removed by fitting standard stellar spectra to the observed photometry. The galaxy surface density in the UltraVISTA/COSMOS field exceeds that in the UDS/SXDS by a factor of ≅1.4, indicating strong cosmic variance between the two fields. The number counts of galaxies we find are a factor of 2 lower than predicted by the recent LF determination by Bouwens et al., and the derived rest-frame UV LF at z ≅6 revealed that an under dense UDS field can account for some of the observed differences between previous analyses. An evolution in the characteristic magnitude between z ≅5 and z≅7 of ∆M*~ 0.5 was found in contrast to other smaller area surveys, and a double power law was shown to equally well describe the LF at z = 6 as compared to the commonly assumed Schechter function. The bright-end of the LF at z ≅6 tentatively shows a steeper decline than found at z ≅7, which could indicate the onset of mass quenching of the most massive galaxies or the rise of dust obscuration. Comparison with the predictions of the latest theoretical models and simulations of galaxies reveals that most models require substantial (A1500 ~ 1.5–2) average dust extinction at the bright end to reproduce the shape of the galaxy UV LF at z ≅7.

My Ph.D. has been composed of work involving the use of far–IR and submm observations of AGN. During this time it has focused on the in- terplay between AGN and their host galaxies and cluster environments. Understanding the role of AGN, and how they affect the evolution of both their host galaxies and surrounding environments, is a pressing concern in cosmological models of the universe, affecting as they do the chemical makeup, star formation rate, and morphology of their host galaxies. In Chapter 2, we focus on attempting to determine whether there is an inherent physical difference between Broad Absorption Line Quasars and non–BAL QSOs using Herschel observations taken at 250, 350 and 500 μm as part of the H–ATLAS (Eales et al. 2010) survey. BAL QSOs have been considered the most visible form of AGN feedback, and therefore are a prime starting point for understanding how galaxy evolution may be affected by the presence of an AGN. By using matched samples of 50 BAL and 329 non–BAL QSOs, we create weighted stacks at each wavelength, finding similar far–IR flux–densities for each sample within the errors. By SED modelling using a simple modified black body (Hildebrand 1983) fit to Mrk 231 and IZw1, we derive likely upper and lower limits for the BAL and non–BAL QSOs in each wavelength, again finding they are consistent within the errors. A bevy of statistical tests run on either population similarly finds no evidence to reject the null hypothesis they are drawn from the same parent population. These results would imply that HiBAL QSOs can be unified with ordinary QSOs within a simple orientation dependent scheme. We cannot make the same distinction for LoBALs or FeLoBALs, which the literature suggests may well be a separate evolutionary phase. In Chapter 3, we determine whether the presence of an AGN correlates to an overdensity of star–forming galaxies in the FIR, as has been found at shorter wavelengths (Falder et al. 2010). For the SHAGs study, 171 AGN were observed and selected at z∼1. By using observations at 250 μm, we are able to trace close to the peak of the grey–body SED created by reprocessing by dust of radiation from young O and B stars. Following data reduction, we determine number counts and correct for completeness within a 1Mpc radius of the central AGN. We find an overdensity on the order of around 0.4 sources per AGN, implying a degree of activity already significantly lower than at higher redshifts. This overdensity appears to be somewhat different between RL AGN and RQQ within 1Mpc. A cor- relation is found between radio luminosity and star formation overdensity, consistent with a stronger dependence found by Falder et al. (2010) at 3.6 μm, and there also appears to be a correlation between stellar mass and star formation overdensity for radio–loud QSOs. The galaxies in the environs of the AGN have LIRG–level luminosities, and are likely the pro- genitors of modern day S0 galaxies, whose population increases steadily from z∼1 to the present day (Postman et al. 2005; Smith et al. 2005). Our work with SCUBA–2, presented in Chapter 4, follows on from a prior sample of X–ray–absorbed QSOs (Stevens et al. 2005). This new sample is composed of more highly–absorbed X–ray QSOs and covers a larger area than the initial sample, so is ideal for an analysis of source counts around AGN at high–redshift. Data from the JCMT have been reduced, and completeness corrections and flux corrections applied to catalogues to determine the number counts around AGN. A comparison background, created using data from the Cosmology Legacy Survey has been used to derive comparison counts. The AGN have been investigated, yet none are detected above 3 at 850 μm, in contrast to the original sample. This may suggest that star formation in their host galaxies has been suppressed. Upon stacking in redshift and BAL classification, no difference in flux– density is apparent and the sources studied here have a similar stacked submm output to an unabsorbed QSO sample created for the original X– ray absorbed QSOs. However, over half of the sources here are BAL QSOs in contrast to the original absorbed QSO sample which contained only 1 BAL QSO. From the work in Chapter 2, one might expect BAL and non–BAL QSOs to have similar flux–densities. We argue that the sources studied in this thesis have likely undergone rapid evolution owing to a strong outflow, and as such star formation has been suppressed sufficiently that the submm emission is below the confusion noise. BAL winds may still be present, but essentially, the show is already over. A similar mechanism may already have occurred in unabsorbed QSOs if all QSOs pass through an X–ray–absorbed phase. With regard to source counts, we find that there is tentative evidence for an overdensity of sources around these AGN. The SFRs of the companion sources have been calculated using several greybody analogues, all of which imply a high degree of activity, suggesting these fields will evolve to become some of the most massive regions at the present epoch, in keeping with current theories of SMGs and high–redshift clusters.

A sample of 296 faint (> 0.5 mJy) radio sources is selected from an area of the Tenth Cambridge (10C) survey at 15.7 GHz in the Lockman Hole. The 10C survey is complete to 0.5 mJy at 15.7 GHz and has a resolution of 30 arcsec. By matching this catalogue to several lower frequency surveys (e.g. including a deep GMRT survey at 610 MHz, a WSRT survey at 1.4 GHz, NVSS, FIRST and WENSS) I have investigated the radio spectral properties of the sources in this sample; all but 30 of the 10C sources are matched to a source in one or more of these surveys. I have found a significant increase in the proportion of flat spectrum sources at flux densities below 1 mJy – the median spectral index between 15.7 GHz and 610 MHz changes from 0.75 for flux densities greater than 1.5 mJy to 0.08 for flux densities less than 0.8 mJy. Thus a population of faint, flat spectrum sources is emerging at flux densities greater than approximately 1 mJy. The spectral index distribution of this sample of sources selected at 15.7 GHz is compared to those of two samples selected at 1.4 GHz from FIRST and NVSS. I find that there is a significant flat spectrum population present in the 10C sample which is missing from the samples selected at 1.4 GHz. The 10C sample is compared to a sample of sources selected from the SKADS Simulated Sky by Wilman et al.; this simulation fails to reproduce the observed spectral index distribution and significantly under predicts the number of sources in the faintest flux density bin. I conclude that it is likely that the observed faint, flat spectrum sources are a result of the cores of FRI sources becoming dominant at high frequencies, rather than the emergence of a new population of starforming galaxies. I have used recent Very Long Baseline Interferometry (VLBI) observations by Middleberg et al. with a resolution of 10 mas to investigate the properties of these faint 10C sources in the Lockman Hole and find that 33 out of the 51 10C sources in the VLBI field (65 percent) are detected by the VLBI observations. The high brightness temperature of these VLBI-detected sources rules out the possibility that this faint, high frequency population is dominated by starbursting or starforming sources and indicates that they must be Active Galactic Nuclei. The sources in the Lockman Hole 10C sample are matched to optical, infrared and Xray data available in the field. A complete sample of 96 sources with high-resolution radio information available is defined; multi-wavelength counterparts are identified for 80 out of the 96 sources in this sample, for which is it possible to derive photometric redshifts. The radioto- optical ratios of these sources show that the 10C sample is almost completely dominated by radio galaxies. 59/80 sources have luminosities greater than the FRI/FRII dividing luminosity. The nature of these radio galaxies is investigated, using the multi-wavelength data to split the sources into high-excitation and low-excitation radio galaxies (HERGs and LERGs respectively). This shows that 34 sources are probably HERGs and 33 are probably LERGs, with 29 which could not be classified at this stage. The properties of these HERGs and LERGs are compared and I find that the HERGs tend to be found at higher redshifts, have flatter spectra, higher flux densities and smaller linear sizes. This study is extended to lower flux densities using new, very deep, observations made with the Arcminute Microkelvin Imager in two fields. I use these observations to extend the 15.7-GHz source count down to 0.1 mJy, a factor of five deeper than the 10C count. These new deeper counts are consistent with the extrapolation of the fit to the 10C count, and do not show any evidence for an upturn. There is therefore no evidence for a new population (e.g. of starforming sources) contributing to the 15.7 GHz source count above 0.1 mJy, and suggesting that the faint, high-frequency population continues to be dominated by radio galaxies. Recent models of the high-frequency source counts under-predict the number of sources observed by a factor of two, consistent with the fact that these models fail to include the dominance of the cores and the faintness of the extended structures of these sources.

The stellar populations harboured by some of the Universe’s earliest galaxies are within observational reach. Determining the details of these stellar populations and their formation histories within the first billion years after the Big Bang is crucial for both understanding the earliest stages of galaxy evolution and for assessing the contribution of early star-forming galaxies to cosmic reionization. This thesis presents observational measurements of the rest-frame UV and optical colours of star-forming Lyman Break galaxies (LBGs) at redshifts 4 < z < 9, and their inferred stellar population parameters. By combining ground-based ~1 deg² surveys with deeper, narrower space-based deep-field surveys, we have constrained the rest-frame UV spectral slope of galaxies over a wide-range of cosmic time (4 < z < 9) and luminosity (−23 < MUV < −17) in a self-consistent way. To do so, we developed simulations to allow the inference of intrinsic colours from noisy, potentially biased observations. With these simulations, a robust UV colour measurement method was devised in preparation for the Hubble Ultra Deep Field 2012 (UDF12) survey. Then, after delivery of the UDF12 data, our technique and simulations were applied to yield the first bias-free measurements of the UV spectral slope of galaxies at z ≈ 7 and 8. We found no support for the previously claimed dominant sub-population of exotically blue, faint galaxies at z ≈ 7. In fact with careful consideration of their errors and selection biases, even the most extreme galaxies we observed can have their colours explained by stellar population synthesis models of unremarkable parameters. Expanding this study to brighter, rarer, galaxies required the inclusion of wide-area ground-based survey data, and consequently a more focused examination of galaxies at z ≈ 5. We selected high signal-to-noise galaxies from four fields, with absolute magnitudes spanning MUV = −22.5 to −17.5, and measured their rest-frame UV spectral slopes. Coupling these measurements with our simulated observations, we were able to determine the width of the intrinsic colour distribution of galaxies at z ≈ 5. We found that brighter galaxies are not only on average redder than their fainter counterparts, but they are also less self-similar in their colours. The redder average UV colours of brighter galaxies can be attributed to those galaxies being either older, or more dust reddened. By pairing these measurements, which are primarily a probe only of the presently forming portion of the stellar population, with those of LBG’s Balmer Breaks, which are more sensitive to bygone star formation, we were able to break this age–dust degeneracy and conclude that, at z ≈ 5, brighter galaxies are more heavily reddened than fainter galaxies even though their stars are no older.

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.

This thesis presents a detailed study of the impact of radio-AGN on star formation and the interstellar medium (ISM) of galaxies across cosmic time. To do this, this thesis uses far-IR/sub-mm data from the Herschel Space Observatory. I create a well-selected sample of 1599 radio sources using the NRAO VLA Sky Survey (NVSS) and Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) data in combination with the UKIRT Infrared Deep Sky Survey - Large Area Survey (UKIDSS - LAS) data. I find that the far-IR luminosities and dust temperatures of radio galaxies are lower in comparison to those of non-radio-detected galaxies. This luminosity deficit grows with increasing stellar mass. I argue that the reasons for these differences is probably due to indirect radio-AGN feedback, i.e. radio jets mechanically heat the halo-environment, preventing external sources of cold gas from entering the host and forming stars. The far-IR luminosity and dust temperature is found to decrease as a function of radio source size. I find the most likely explanation for this is jet-induced star formation while the jets are confined to the ISM. Finally, a method for identifying reliable high-z, star-bursting radio sources in the H-ATLAS is described with which statistically significant studies of radio-jet induced star formation may be undertaken.

I have investigated the properties of the large scale structure of the nearby Universe using data from the Galaxy and Mass Assembly survey (GAMA). I generated complementary halo mass estimates for all groups in the GAMA Galaxy Group Catalogue (G³C) using a modified caustic mass estimation algorithm. On average, the caustic mass estimates agree with dynamical mass estimates within a factor of 2 in 90% of groups. A volume limited sample of these groups and galaxies are used to generate the large scale structure catalogue. An adapted minimal spanning tree algorithm is used to identify and classify structures, detecting 643 filaments that measure up to 200 Mpc/h, each containing 8 groups on average. A secondary population of smaller coherent structures, dubbed `tendrils,' that link filaments together or penetrate into voids are also detected. On average, tendrils measure around 10 Mpc/h and contain 6 galaxies. The so-called line correlation function is used to prove that tendrils are real structures rather than accidental alignments. A population of isolated void galaxies are also identified. The properties of filaments and tendrils in observed and mock GAMA galaxy catalogues agree well. I go on to show that voids from other surveys that overlap with GAMA regions contain a large number of galaxies, primarily belonging to tendrils. This implies that void sizes are strongly dependent on the number density and sensitivity limits of the galaxies observed by a survey. Finally, I examine the properties of galaxies in different environments, finding that galaxies in filaments tend to be early-type, bright, spheroidal, and red whilst those in voids are typically the opposite: blue, late-type, and more faint. I show that group mass does not correlate with the brightness and morphologies of galaxies and that the primary driver of galaxy evolution is stellar mass.

In this thesis I investigate the hosts and cluster environments of a sample of 41 radio galaxies between z = 0.4 and z = 0.6. I use spectroscopic data for a 24 object subsample to investigate their star formation histories via the strength of the 4000A break. I find that the higher radio luminosity or high excitation objects in the sample have evidence for young stellar populations, but the lower radio luminosity or low excitation objects do not. My investigations into the Fundamental Plane (FP) of 18 of the radio galaxies, using the same spectroscopic data as well as data from the literature, show that the Fanaroff- Riley type I objects (FRIs) lie on the FP of local radio galaxies once corrected for passive evolution but the Fanaroff-Riley type II objects (FRIIs) do not. I suggest that an evolution in the size of the host galaxies, aided by a combination of passive evolution and a mass-dependent evolution in the mass-to-light ratios, may explain the observed offsets. Finally, I use wide field multi-band imaging to investigate the cluster environments of the full z ~ 0.5 sample. I find that the environmental overdensity is positively correlated with the radio luminosity and observe a greater number of close companions around the FRIIs than the FRIs (albeit with only nine FRIs in the sample). The cluster environments of the radio galaxies with the greatest host luminosities show tentative evidence for an alignment between the major axis of a galaxy and that of its cluster, whilst there are hints that the objects with the highest radio luminosities have clusters whose major axis is aligned with the position angle of the radio jet. My results suggest a picture in which FRII type radio sources reside in particularly rich cluster environments at z ~ 0.5 but FRI type radio sources in less rich environments. The environment plays a key role in determining both the radio properties of the galaxy and the evolution of its host. The effect of the environment on the emission line properties and star formation histories of the galaxies leads to the overlap seen in the morphological and spectral properties of radio galaxies.

The centrepiece of this thesis is a deep, new, high-resolution 1.4-GHz image covering the United Kingdom Infrared (IR) Telescope IR Deep Sky Survey (UKIDSS) Ultra Deep Survey (UDS) legacy field. Deep pseudo-continuum observations were made using the Very Large Array, prior to its recent upgrade, in its A, B and DnC configurations. The resulting mosaic has a full-width-at-half-maximum synthesised beam width of ≈ 1.7 arcsec and a point-source sensitivity of ≈ 60μJy (6σ ) across the central 0.6 deg2, while conserving flux from sources of extended emission. The full image covers 1.3 deg2. I also present a catalogue containing over 1,000 radio emitters, having chosen the 6-σ threshold by maximising the number of radio sources with secure optical/near-IR counterparts. Most of the sources in the catalogue (≈ 90 per cent) lie in the sub-mJy flux density regime. Deep, complementary data covering a wide range of wavelengths was used to explore this faint radio population, whose nature remains controversial. It was found that 53 per cent of the sample comprise active galactic nuclei (AGN). AGN dominate at & 0.2mJy and remain a significant population down to 0.1mJy; at lower fluxes – the so-called μJy radio population – star-forming galaxies become dominant. The radio sample presented here was also matched to Hubble Space Telescope imaging of the UDS field (which is part of the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey – CANDELS) to classify the faint radio population morphologically. These classifications were done using the Gini–M20 method. It was found that a low fraction of AGN and SFGs are undergoing interactions and mergers, 33 ± 9 and 13 ± 7 per cent, respectively. The merger fraction does not appear to have evolved significantly since z ∼ 3. This suggests that mergers have played a relatively minor role in the assembly of galaxies and super-massive black holes – certainly less significant than previously thought. Finally, I present a study of cosmic star-formation activity as a function of stellar mass and redshift, exploiting panchromatic stacking. Mid-IR–through–radio images, including new data from Herschel, are stacked at the positions of a K-selected (i.e. an approximately mass-selected) sample in the UDS field. Specific star-formation rates (SSFR, i.e. star-formation rate per stellar mass, or the rate at which a galaxy is converting its gas into stars) were derived from UDS radio luminosities measured here and stellar masses from the literature. The SSFR was found to be poorly correlated with stellar mass; it decreases with decreasing redshift; at a given mass, SSFR rises with redshift. These results indicate that at early epochs, galaxies were forming stars more efficiently and at a higher rate.

We present new measures of the rotation curves of disc galaxies from z~0.2 to z~1.7, using deep exposures from both DEIMOS and LRIS spectrographs on the Keck telescopes in combination with multi-band imaging from the Hubble Space Telescope. We do this with a new modelling code, curvation, which has been optimised to extract the rotation velocity measurements from galaxies at intermediate and high redshift. To this end, we conduct a bulge-to-disc de-composition to allow us to de-project observed velocities to extract a model of the intrinsic rotation curve. We demonstrate the improved accuracy and precision of these measurements via a number of tests, but primarily in recovering an intrinsic scatter of the high redshift Tully-Fisher relation which is similar to that found locally. We show for the first time that the stellar mass Tully-Fisher relation is tightly in place at z~1, the normalisation of which has evolved less than 0.02±0.02 dex in stellar mass from z~1.7 to z~0.2. We do however see evidence for evolution in classic B-band Tully-Fisher relation, which is brighter at z~1 by 0.85±0.28 magnitudes than that at z~0.3. This trend is consistent with what was previously known about the evolving star-formation rates of disc galaxies. We then explore the potential drivers of these trends in the Tully-Fisher relation by estimating the baryonic and dark matter content of our galaxies. We also discover a surprising trend in the bulgeless disc galaxies at high redshift, which may be evolving differently from other rotationally supported galaxies. In the context of work which has been conducted at z~2, we discuss our results of a stellar mass Tully-Fisher relation which is strikingly similar over two-thirds of the age of the Universe.

This thesis presents spectroscopic observations of z ≥ 7 galaxy candidates in the Hubble Ultra Deep Field, which were selected with HST WFC3 imaging, using the Lyman-Break technique. Four z-band (z ≈ 7) dropout galaxies were targeted with Gemini/GNIRS, one z-band dropout galaxy and three Y -band (z ≈ 8 − 9) dropout galaxies with VLT/XSHOOTER, and 22 z-band dropouts with VLT/FORS2, where 15 of the latter are strong candidates. No evidence of Lyman-α emission is found, and the upper limits on the Lyman-α flux and the broad-band magnitudes are used to constrain the rest-frame equivalent widths for this line emission. Amongst the targeted objects, observations were made of HUDF.YD3, a relatively bright Y -band dropout galaxy likely to be at z ≈ 8 − 9 on the basis of its colours in the HST ACS and WFC3 images. Lehnert et al. (2010) observed this galaxy using the VLT/SINFONI integral field spectrograph and claim that it exhibits Lyman-α emission at z = 8.55. In observations of this object described in this thesis, which were made with VLT/XSHOOTER and Subaru/MOIRCS, this line was not reproduced despite the expected signal in the combined MOIRCS & XSHOOTER data being 5σ. Hence it appears unlikely that the reported Lyman-α line emission at z > 8 is real. Accounting for incomplete spectral coverage, in total (across all spectro- graphs) 9.63 z-band dropouts and 1.15 Y -band dropouts are surveyed to a Lyman-α rest-frame Equivalent Width better than 75 ̊A. A model where the fraction of high rest-frame equivalent width emitters follows the trend seen at z = 3−6.5 is inconsistent with these non-detections at z = 7−9 at a confidence level of ∼ 91%, which may indicate that a significant neutral HI fraction (χHI) in the intergalactic medium suppresses the Lyman-α line at z > 7. In particular, the lack of detection of Lyman-α emission in this spectroscopy is compared with results at lower redshift by Stark et al. (2010), who derive a mapping between Lyman-α fractions and χHI based on radiative transfer simulations by McQuinn et al. (2007). These results suggest a lower limit of χHI ~ 0.5.

A unique K-band selected high-redshift spectroscopic dataset (UDSz) is exploited to gain further understanding of galaxy evolution at z > 1. Acquired as part of an ESO Large Programme, this thesis presents the reduction and analysis of a sample of ∼ 450 deep optical spectra of a random 1 in 6 sample of the KAB < 23, z > 1 galaxy population. Based on the final reduced dataset, spectrophotometric modelling of the optical spectra and multi-wavelength photometry available for each galaxy is performed using a combination of single and dual component stellar population models. The stellarmass and age estimates provided by the spectrophotometric modelling are exploited throughout the rest of the thesis to investigate the evolution of massive galaxies at z > 1. Focusing on a K-band bright (K < 21.5) sub-sample in the redshift range 1.3 < z < 1.5 the galaxy size-mass relation has been studied in detailed. In agreement with some previous studies it is found that massive, old, early-type galaxies (ETGs) have characteristic radii a factor ~- 1.5 − 3.0 smaller than their local counterparts at a given stellar-mass. Due to the potential errors in spectrophotometric estimates of the stellarmasses at high redshift velocity dispersion measurements are derived for a sub-sample of massive ETGs at z > 1.3 in order to calculate dynamical mass estimates. To date, only a handful of objects at z > 1.3 have individual velocity dispersion estimates in the literature. Here the largest single sample (13 objects) of velocity dispersion measurements at high redshift is presented. The results for the sub-sample of objects with dynamical mass estimates confirm the results based on stellar mass estimates that high redshift massive systems are more compact than their local counterparts. The fraction of K-band bright objects at high redshift that are passively evolving is calculated with specific star-formation rates from the UV rest-frame continuum, [OII] emission and 24μm data. It is concluded that ∼ 58 ± 10% of the K < 21.5, 1.3 < z < 1.5 galaxy population is passively evolving. Various photometric techniques for separating star-forming and passively evolving galaxies are assessed by exploiting the accurate spectral types derived for the UDSz spectroscopic sample. Popular highredshift selection techniques are shown to fail to effectively select complete samples of passive objects with low levels of contamination. Using detailed information available for the UDSz dataset, various techniques are optimised and then used to estimate the passive fraction from the full UDS photometric catalog. The passive fraction results from the full photometric catalog are found to agree well with the results derived from the UDSz sample. With the Visible and Infrared Survey Telescope for Astronomy (VISTA) now starting to produce data, the opportunity has been taken to develop high-redshift galaxy population dividers based on the VISTA filters. Using the first data release from the VISTA Deep Extragalactic Observations (VIDEO) survey (VVDS D1 field), the passive fractions of K-band limited samples have been estimated to compare with results derived in the UDS. Within the errors the passive fraction estimates in the UDS and VISTA VVDS D1 field are found to agree reasonably well. Finally, composite spectra are used to study the evolution of various different galaxy sub-samples as a function of redshift, age, stellar-mass and specific star-formation rate. This work produces an remarkably clean result, showing that the massive, absolute Kband bright, passively evolving ETGs are always the oldest population, with ages close to the age of the Universe at z ∼ 1.4. In contrast, the late-type, low-mass, star-forming galaxies are always found to be much younger systems. This result strongly supports the downsizing scenario, in which more massive systems complete their stellar-mass assembly before lower-mass counterparts.

The role of the Anthropic Principle in astrophysics and cosmology is examined in two principal parts. The first (minor) part takes a chiefly philosophical perspective and examines the manner in which human cognition features into discussions on cosmic origins. It is shown that the philosophical questions raised by the Anthropic Principle and ‘fine-tuning of life’ bear resemblances to problems within the philosophy of mind and we seek a common origin for this surprising parallel. A form of ‘epistemic structural realism’ is defended and used to critique the physicalist identity thesis. It is argued that equating ‘reality’ with mathematical structures, which is the basis of the identity thesis, leads to incoherent conclusions. Similar reasoning is used to critique infinite Multiverse theories. In the second (major) part, we gradually transition into mainstream astrophysics, first presenting a new line of research to explore counterfactual universes using semi-analytic models (SAMs) and offering a preliminary study wherein the cosmological constant is varied and the effects on ‘advanced civilisations’ are examined. The importance of galaxy mergers is highlighted and leads to their study. We first try solving the pattern-recognition problem of locating mergers using the Galaxy Zoo database and produce the largest homogenous merger catalogue to date. We examine their properties and compare them with the SAMs of the Millennium Simulation finding good general agreement. We develop the Galaxy Zoo approach with a new visual-interface design and double the size of the merger catalogue of SDSS mergers in the local Universe.

This thesis explores the evolution of galaxies from the onset of star formation shortly after the Big Bang until the present day. Particular emphasis lies on the redshift range z = 1.4 2.5, the so-called “redshift desert”, as it coincides with the peak epoch of cosmic star formation activity and mass assembly. Most of the information about galaxies and their evolution arrives in the form of their integrated light, i.e. the conglomeration of light emitted by stars of various ages and metallicities. In order to interpret the observed spectra and magnitudes, and to extract the physical parameters we therefore require models. This holds true in particular for galaxies too faint to target them spectroscopically, and for which redshifts and physical parameters derived from only their photometry is the only feasible way to study them in more detail. This thesis is concerned with such models, and describes how GALEV evolutionary synthesis models describe the spectral and chemical evolution of galaxies, accounting for gaseous emission and the increasing initial abundances of successive stellar generations, how they compare to observations and what we can learn from their application. Based on a large model grid, covering all observed galaxy evolution stages, I find that sub-solar metallicities have significant impact on the spectra of galaxies, and can lead to systematic errors and biases if not accounted for. A comparison of models with different metallicities furthermore reveals that photometric redshifts are also systematically biased if sub-solar metallicities are not properly accounted for. I also note that even a small mass-fractions of young stars can dominate the overall spectrum, leading to a large underestimation of the mass and age of the stellar population. The models explain not only the colour evolution of galaxies observed at a range of redshifts, but also their physical parameters. I show that with magnitudes in only a few bands we can successfully explain not only the masses of galaxies, but also their star formation rates and, where available from observations, their metallicities. If additional data are available, the grid of models can be used to refine colour selection criteria and to break degeneracies, e.g. between dust-reddened actively star-forming galaxies and intrinsically old, passively evolving galaxies. Using GAZELLE, a photometric redshift code that is purpose-tailored to harmonise with these models, I can extract accurate redshifts and a wealth of physical parameters from the largest ever sample of observed multi-wavelength photometry of galaxies. I then compare our findings with semi-analytical models that trace the evolution of individual galaxies based on cosmological simulations. In my sample I find a significant population of high-mass galaxies that is not accounted for by this class of models. Furthermore a small percentage of massive, yet starforming galaxies challenges our idea on how these galaxies form and evolve. In an appendix to this thesis I present a complementary approach to reconstruct the evolution of galaxies, using star clusters as tracers. I introduce a new technique to break the age-metallicity degeneracy and obtain individual ages and metallicities for a sample of globular clusters, revealing a merger of two Sb/Sc-type spirals 2 Gyrs ago in NGC 4570, a lenticular galaxy in the Virgo cluster. Also in the appendix I show that, at least in the studied galaxy Arp 78, the initial mass function conforms with our assumptions and does not change in low-density environments as recently predicted. Although studies of galaxy evolution are a major field in astronomy, there is still a lot more to be done to reveal the inner workings of these island universes, and this thesis also addresses how to continue and improve the work presented herein.

In this thesis I investigate the dynamics and stellar populations of a sample of 28 edge-on early-type (S0--Sb) disk galaxies, 22 of which host a boxy or peanut-shaped bulge. I begin by constructing mass models of the galaxies based on their observed photometry and stellar kinematics. Subject to cosmologically motivated assumptions about the shape of dark haloes, I measure in a purely dynamical way their stellar and dark masses. I make a preliminary comparison between the dynamically determined stellar masses and those predicted by stellar population models. I then compare the Tully-Fisher (luminosity--velocity) relations of the spirals and S0s in the sample. I show that S0s are systematically fainter at a given rotational velocity, but the amount by which they are fainter is less than expected by models in which they are the products of truncation of star formation in spirals. This raises the possibility that S0s are smaller or more concentrated than spirals of the same mass. I then study the vertical structure of the boxy and peanut-shaped bulges of a subset of the sample. Among this sample of five galaxies, I find one example in which the stellar populations show no evidence that the bulge and the disk formed in different processes, and in which the bulge is in perfectly cylindrical rotation, i.e. its line-of-sight velocity does not change with height above the disk. This galaxy is probably a pure disk galaxy. However, even with this small sample, I also show that cylindrical rotation and homogeneous stellar populations are not ubiquitous properties of boxy and peanut-shaped bulges. Finally I analyse central and radial trends in the stellar populations of the bulges of full sample of 28 galaxies. I find that, at a given velocity dispersion, the central stellar populations of these barred early-type disk galaxies are identical to those of elliptical galaxies, which suggests that secular evolution does not dominate the centre of these galaxies. However, the radial metallicity gradients are shallower than those of ellipticals. This is qualitatively consistent with chemodynamical models of bar formation, in which radial inflow and outflow smears out pre-existing gradients.

In this work I have examined the spatially resolved properties of the local early- type galaxy population. Using Hubble Space Telescope and ground based pho- tometry I constructed Jeans Anisotropic Multi Gaussian Expansion models of the SAURON sample of early-type galaxies, from which I determined the depth of the local gravitational potential well, quantified by the local escape velocity, Vesc. I found that Vesc correlated tightly with the three Lick indices: Mgb, Fe5015 and Hβ. The Mgb-Vesc relation within individual galaxies is identical to that between different galaxies; the relation is both local and global. The Mgb-Vesc relation is: log Mgb = (0.35 ± 0.01) log Vesc − (0.41 ± 0.03). While the metallicity, [Z/H] is cor- related with Vesc it does not show the same local and global behaviour. Age (t) and alpha enhancement ([α/Fe]) are only weakly correlated with Vesc. A combination of [Z/H] and t is tightly correlated with Vesc, with scatter comparable to the Mgb-Vesc relation, and does show the local and global behaviour. This combination is given by: log Vesc = 0.85[Z/H] + 0.43 log t. Using the volume limited ATLAS3D sample of 260 local ETGs I examined in detail the behaviour of the Mgb-Vesc relation and its dependence on other galaxy properties. I found that systematic deviations from the relation correlate with the local environmental density and molecular gas mass of a galaxy, and with the local [α/Fe] measurement. I found that there is a population of galaxies that do not follow the relation, found only at Vesc < 400 kms−1. These galaxies have negative gradients, high central Hβ indices and young (t < 3 Gyrs) ages. Using stellar population models I demonstrated that these negative gradient galaxies are perturbed from the relation by recent star formation and will return to the relation as they age. I also describe the observation, reduction and analysis of a new sample of ETGs in the core of the Coma cluster, the highest density environment in the local Universe, observed with the SWIFT Integral Field Spectrograph. I determined the fraction of slow rotators in the sample, comparing it to results from the ATLAS3D survey, and found an enhanced slow rotator fraction in the Coma cluster. I also determined the Fundamental Plane of Coma early-type galaxies, given by: log Re = (1.20 ± 0.22) log σe − (0.79 ± 0.09) log⟨Ie⟩.

This thesis is concerned with the targeting of emission line galaxies with FMOS (Fibre Multi-Object Spectrograph) to determine properties of star forming galaxies at redshift ~1.5, and provide measurements of the growth rate of large-scale structure through Redshift Space Distortions (RSDs). I also consider the opportunities of targeting the passive galaxy population at high redshift, through measurements of their continuum. I start with the extensive broad-band photometric data available in the UKIDSS-UDS (United Kingdom Infrared Telescope Deep Sky Survey - Ultra-Deep Survey) field which is used to produce a band-merged catalogue, later used for determining photometric redshifts. In producing this catalogue, I approach the issue of source confusion present in the deep Spitzer imaging using z-band priors on profile position and shape and an iterative Expectation-Maximisation algorithm. Photometric redshift estimates are compared against colour selections as potential targeting techniques for a wide-area redshift survey with FMOS. Different photometry survey areas are considered, and the quality of selection given the available broad-band data tested, by adjusting the photometric catalogue produced for the UDS. The results indicate that the SWIRE (Spitzer Wide area InfraRed Extragalactic Survey) fields are too small to provide adequate sources with a consistent selection mechanism. The CFHTLS (Canada-Frace-Hawaii Telescope Legacy Survey) would have a large enough area given deeper z'-band imaging, and SWIRE-depth coverage in the Spitzer 3.6μm and 4.5μm bands. I present FMOS commissioning data obtained for the UDS field, including the spectroscopic targeting of sources form the High-Z Emission Line Survey (HiZELS). With this data, I am able to test the current quality of flux calibration using cool stars targeted simultaneously and the level of systematic errors left by sky-subtraction. The sample of HiZELS sources selected to place Hα at z~1.45 show low contamination from other emission lines, and only one out of 9 targets assigned a redshift has any indication of AGN activity. Finally, I present longslit observations of faint, passive galaxies at redshift z~1.9, selected as members of a possible cluster, JKCS 041, selected from broad band colours. One object was observed with high enough signal to noise to constrain the position of the 4000 Å / Balmer break, providing a tighter constraint on the photometric redshift of 1.8867 +0.0034 -0.0117.