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Until recently, obtaining rest-frame optical spectra of galaxies at z > 1 was a time consuming and challenging observation due to the difficult nature of near-infrared (near-IR) spectroscopy. However, with the advent of second generation ground-based near-IR spectrographs (e.g. KMOS, MOSFIRE), and the new low resolution near-IR grisms on the Hubble Space Telescope (HST), we have entered a new era in the study of high redshift galaxies. This thesis explores the physical properties of star-forming galaxies in the redshift range 1 < z < 3 by utilising a custom reduction of the 3D-HST near-IR grism spectroscopic survey. One of the most important observational constraints on the evolution of galaxies is the mass-metallicity relation (MZR), which is sensitive to both the star-formation history and various inflow/outflow processes. I use the 3D-HST spectra to provide a new constraint on the MZR at 2:0 < z < 2:3, and moreover measure the O/H abundance directly from the oxygen and hydrogen emission lines ([OII], [OIII] and Hβ) as opposed to the more common method at high redshift of inferring O/H from the N/H ratio (via [NII] and Hα). I show that the traditional form of the MZR is recovered from the 3D-HST data, with metallicity increasing with the stellar mass of a galaxy. However, the absolute metallicity values I derive are inconsistent with previous N/H-based measurements of metallicity at these redshifts. Moreover, I show that the 3D-HST data is inconsistent with the `fundamental metallicity relation' (FMR), and that, contrary to previous claims, this local Universe relation may not hold out to z & 2. To investigate this metallicity discrepancy further, I measure the evolution of the [OIII]/Hβ nebular emission line ratio in the 3D-HST spectra over the redshift range 1:3 < z < 2:3. I compare this observed line ratio evolution with state-of-the- art theoretical models which take into account the independent evolution of the ionization parameter, electron density and metallicity of star-forming regions with redshift. The homogeneous 3D-HST dataset allows me to perform a consistent analysis of this evolution which takes into account line luminosity selection effects. I show that, according to models, the observed [OIII]/Hβ evolution cannot be accounted for by pure metallicity evolution. Instead I am able to infer that the line ratio evolution is more consistent with, at the very least, an evolution to stronger ionizing conditions at high redshift, and perhaps even denser star-forming regions. I explore how this result can also explain the observed discrepancy between high redshift metallicity measurements. In light of this finding, I revisit the MZR at z >~ 2 and employ a purely theoretical approach to inferring metallicities from nebular lines, which is able to account for an evolution in ionization conditions. I then use a selection of galaxies from the local Universe, which mimic the properties of high redshift galaxies, to derive a more robust ionization sensitive, conversion, between N/H and O/H. With this new conversion which I am able to bring the previous inconsistent metallicity measurements at z >~ 2 back into agreement. Finally, I am able to show that, in this new formalism, the metallicity evolution between z = 2 and z = 3 is perhaps not as large as previously reported. To conclude I discuss ongoing work as part of the KMOS Deep Survey (KDS) being undertaken with the near near-IR Multi-Object Spectrograph KMOS on the VLT. I describe the observations and data reduction that has been completed to date and describe how this instrument will allow me to extend the work presented in this thesis to z > 3. I also introduce FIGS, a new HST near-IR grism survey seeking to spectroscopically identify galaxies at 5:5 < z < 8:5 and work I have begun in exploring this dataset.

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.

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.

This thesis presents multi-frequency data, galaxy identifications, estimated redshifts, and derived physical properties for the sub-millimetre source sample produced by the SCUBA HAlf Degree Extragalactic Survey (SHADES). SHADES is the largest, complete, sub-millimetre survey undertaken to date, and the aim of this work is to exploit this survey to study the evolution of sub-mm selected galaxies at high redshift, explore their possible connectionwith localmassive ellipticals, and to test current models of galaxy formation. The SHADES sample was selected from 850 micron images made with the submillimetre camera SCUBA at the James Clerk Maxwell Telescope. These submillimetre maps cover a total area of 720 arcmin2 split between two well-studied extra-galactic survey fields, the Lockman Hole East and the Subaru/XMMNewton Deep Field (SXDF). The resulting sample of 120 sub-millimetre sources is the focus of this thesis. Here the wealth of information provided by deep radio, optical, near-infrared and mid-infrared imaging of the two SHADES fields is exploited to complete the identification of the SHADES sample, and then to derive a robust redshift estimate for every sub-millimetre source. Where possible this is achieved from the optical+ infrared photometry using a new two-component redshift estimation code developed specifically to deal with starbursting galaxies with potentially highly stochastic star-formation histories. The effectiveness of this code is demonstrated via comparison with the small subset of SHADES source which possess robust spectroscopic redshifts. For those galaxies which are too faint for effective redshift constraints to be provided by the existing optical+infrared photometry, the information on the long-wavelength spectral energy distribution provided by the radio+submm photometry is utilised to provide cruder constraints or limits on redshift. The result is the first complete and unbiased estimate of the redshift distribution of the bright extragalactic sub-millimetre galaxy population. It is found that the brightest sub-mm sources are confined to the redshift range 2 < z < 4, while more moderate luminosity sources span the full range of redshift out to z ∼ 5. The fits to themulti-frequency photometry provided by the redshift estimation technique are also used to derive estimates of the stellar mass, and star-formation history of each SHADES galaxy. The average derived stellar mass is ∼ 3 × 1011 M⊙ and it is found that the violent starburst powering the sub-millimetre emission typically contributes less than 10% of the stellar mass of the galaxy which has been assembled prior to the “current” starburst event. The distributions of redshift, stellar mass, and star-burst ages are compared with the predictions of a range of galaxy models, including the suite of models originally used to motivate the SHADES survey in van Kampen et al. (2005), and themost recent incarnation of the Durhamsemi-analytic galaxy formationmodels described by Swinbank et al. (2008). It is found that the redshift distribution and sub-mmflux versus redshift for bright sub-mmgalaxies can be reproduced best by one of the van Kampen models, which is based on semi-analytic modelling with a Chabrier IMF. We can rule out the non-semi-analytic prediction models and the Durham semi-analytic model with a top-heavy IMF. However the stellar masses are systematically underpredicted by all of the models. Either the stellar masses derived from the SHADES data have been systematically over-estimated, or the models need to be modified (perhaps by the inclusion of AGN feedback) to allow larger galaxy masses to assembled prior to z ∼ 2. Finally, it is demonstrated that themass in place prior to the observed starburst cannot have been produced by an analogous super-burst at higher redshift, but rather requires to have been assembledmore gradually over a timescale of ∼ 1−2 Gyr. It is thus concluded thatmassive galaxies undergo theirmost violent phase of star formation at redshifts 2 < z < 4, but that the enormous starbursts which lead to detection in current sub-millimetre surveys can only take place in the potential well provided by an already massive galaxy. This supports a scenario in which bright sub-millimetre galaxies are indeed the progenitors of the massive elliptical galaxies found in the local Universe.