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We present first results from the KMOS Ultra-deep Rotation Velocity Survey (KURVS), aimed at studying the outer rotation curves shape and dark matter content of 22 star-forming galaxies at $z\sim1.5$. These galaxies represent `typical' star-forming discs at $z \sim 1.5$, being located within the star-forming main sequence and stellar mass-size relation with stellar masses $9.5\leqslant$log$(M_{\star}/\mathrm{M_{\odot}})\leqslant11.5$. We extract individual rotation curves out to 4 times the effective radius, on average, or $\sim 10-15$ kpc. Most rotation curves are flat or rising between three- and six-disc scale radii. Only three objects with dispersion-dominated dynamics ($v_{\rm rot}/\sigma_0\sim0.2$) have declining outer rotation curves at more than 5$\sigma$ significance. After accounting for seeing and pressure support, the nine rotation-dominated discs with $v_{\rm rot}/\sigma_0\geqslant1.5$ have average dark matter fractions of $50 \pm 20\%$ at the effective radius, similar to local discs. Together with previous observations of star-forming galaxies at cosmic noon, our measurements suggest a trend of declining dark matter fraction with increasing stellar mass and stellar mass surface density at the effective radius. Simulated EAGLE galaxies are in quantitative agreement with observations up to log$(M_{\star}R_{\rm eff}^{-2}/\mathrm{M_{\odot}kpc^{-2}}) \sim 9.2$, and over-predict the dark matter fraction of galaxies with higher mass surface densities by a factor of $\sim 3$. We conclude that the dynamics of typical rotationally-supported discs at $z \sim 1.5$ is dominated by dark matter from effective radius scales, in broad agreement with cosmological models. The tension with observations at high stellar mass surface density suggests that the prescriptions for baryonic processes occurring in the most massive galaxies (such as bulge growth and quenching) need to be reassessed., Comment: 23 pages, 9 figures. Resubmitted to MNRAS after addressing the referee's comments. Abstract slightly modified to compile with the arXiv formatting

Solar System Science with the ELTs was a two-part workshop, Part I of which took place virtually on 28 April 2022, followed by Part II as a hybrid meeting at ESO headquarters on 13–15 June 2022. The main motivation for the meeting was to engage the community of Solar System observers in preparation for the forthcoming extremely large telescopes. A special emphasis was placed on exploring how ESO’s Extremely Large Telescope (ESO’s ELT), alongside the Giant Magellan Telescope (GMT) and the Thirty Meter Telescope (TMT), will fit into the expanding landscape of ground- and space-based facilities and transform Solar System research. The meeting brought together instrument experts and observers at all career stages, working on six continents, and representing the different sub-fields of planetary science. A Zenodo collection of the workshop presentations and discussions was publicly released to the community as a valuable resource to inspire and facilitate the development of the first extremely large telescope observing programmes. Solar System Science with the ELTs was envisaged as the first of the three-part conference series Extremely Big Eyes on the Solar System and set the stage for two further workshops in North America and Asia., Published in The Messenger vol. 189, pp. 48-50, December 2022.

Since 2005 ESO has been working with its community and industry to develop an extremely large optical/infrared telescope. ESO's Extremely Large Telescope, or ELT for short, is a revolutionary ground-based telescope that will have a 39-metre main mirror and will be the largest visible and infrared light telescope in the world. To address specific topics that are needed for the science operations and calibrations of the telescope, thirteen specific working groups were created to coordinate the effort between ESO, the instrument consortia, and the wider community. We describe here the goals of these working groups as well as their achievements so far., Comment: 8 pages, 4 figures

ESO regularly updates its science- driven perspective in order to provide the best facilities and services for its community. As part of this exercise, ESO polled its users between January and February 2020. Questions were inspired by the previous poll, conducted in 2015, to probe any evolution of community opinions and profile, with an emphasis on the future of the Very Large Telescope (VLT) and the VLT Interferometer (VLTI). Of the approximately 17700 registered users targeted, 10% had accounts in both the ESO and European ALMA portals, another 14% were registered in the ALMA portal only, and the remaining 76% were registered in the ESO portal only. Some 3700 email addresses, predominantly associated with the ESO portal, were invalid. From the remaining approximately 14000 user accounts, 1673 complete responses were received, a response rate comparable to that of the 2015 poll. The present poll was split into three parts: 1) profile of respondent; 2) current and future observing facilities; 3) ESO in the coming decade. Here we summarise the results and provide some highlights from the poll., Published in The Messenger vol. 184, pp. 8-14, September 2021.

Design and construction of the instruments for ESO’s Extremely Large Telescope (ELT) began in 2015. We present here a brief overview of the status of the ELT Instrumentation Plan. Dedicated articles on each instrument are presented elsewhere in this volume., Published in The Messenger vol. 182, pp. 3-6, March 2021.

The Extremely Large Telescope (ELT) is at the core of ESO���s vision to deliver the largest optical and infrared telescope in the world. Following on from our previous Messenger articles we continue with the description of the optical elements of the ELT. In this article we focus on the quintenary mirror (M5), the field stabilisation unit. In combination with the M4 mirror, M5 is vital to delivering the sharp diffraction limited images needed for science by correcting for the vibrations of the telescope, wind shaking and the atmosphere. We describe the main characteristics of the M5, as well as the challenges and complexity of this unique field stabilisation unit and its design and manufacturing status., Published in The Messenger vol. 185, pp. 3-6, December 2021.

MOONS is the new Multi-Object Optical and Near-infrared Spectrograph currently under construction for the Very Large Telescope (VLT) at ESO. This remarkable instrument combines, for the first time, the collecting power of an 8-m telescope, 1000 fibres with individual robotic positioners, and both low- and high-resolution simultaneous spectral coverage across the 0.64-1.8 micron wavelength range. This facility will provide the astronomical community with a powerful, world-leading instrument able to serve a wide range of Galactic, extragalactic and cosmological studies. Construction is now proceeding full steam ahead and this overview article presents some of the science goals and the technical description of the MOONS instrument. More detailed information on the MOONS surveys is provided in the other dedicated articles in this Messenger issue., Comment: 8 pages, 5 Figures, Published on the ESO Messenger No. 180

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The Extremely Large Telescope (ELT) is at the core of ESO’s vision to deliver the largest optical and infrared telescope in the world. Following on from our previous Messenger article describing the primary mirror (M1), here we focus on the secondary (M2) and the tertiary (M3) mirrors of the ELT, outlining the complexity and challenges involved, and the current manufacturing status., Published in The Messenger vol. 176, pp. 13-15, June 2019.

The Extremely Large Telescope (ELT) is at the core of ESO’s vision to deliver the largest optical and infrared telescope in the world. Continuing our series of Messenger articles describing the optical elements of the ELT, we focus here on the quaternary mirror (M4), a true technological wonder; it is the largest deformable mirror ever made. In combination with M5, M4 is vital to delivering the sharp (diffraction-limited) images needed for science by correcting for atmospheric turbulence and the vibrations of the telescope itself. Here we describe the main characteristics of M4, the challenges and complexity involved in the production of this unique adaptive mirror, and its manufacturing status., Published in The Messenger vol. 178, pp. 3-4, December 2019.

The Extremely Large Telescope (ELT) is at the core of ESO’s vision to deliver the largest optical and infrared telescope in the world. With its unrivalled sensitivity and angular resolution the ELT will transform our view of the Universe: from exoplanets to resolved stellar populations, from galaxy evolution to cosmology and fundamental physics. This article focuses on one of the most challenging aspects of the entire programme, the 39-metre primary mirror (M1). 2017 was a particularly intense year for M1, the main highlight being the approval by ESO’s Council to proceed with construction of the entire mirror. In addition, several contracts have been placed to ensure that the giant primary mirror will be operational at first light., Published in The Messenger vol. 171, pp. 20-23, March 2018.

This poster present dynamical measurements from the KMOS (K-band Multi-Object Spectrograph) Deep Survey (KDS), which is comprised of 78 typical star-forming galaxies at z = 3.5 in the mass range 9.0 < log(M*) < 10.5. We fit spatially and spectrally convolved mock datacubes to the observed data, in order to make beam-smearing corrected measurements of the intrinsic velocity dispersions and rotation velocities of 33 galaxies in the sample classed as spatially resolved and isolated. The results suggest that the rotation-dominated galaxies in the sample are offset to lower velocities at fixed stellar mass and have higher velocity dispersions than star-forming galaxies in the local and intermediate redshift universe. Only 1/3 of the galaxies in the sample are dominated by rotation, which hints that random motions are playing an increasingly significant role in supporting the dynamical mass in the systems. When searching for evolution in scaling relations, such as the stellar mass Tully-Fisher relation, it is important to take these random motions into account.

We analyze the redshift- and luminosity-dependent sizes of dropout galaxy candidates in the redshift range z ~ 7-12 using deep images from the 2012 Hubble Ultra Deep Field (UDF12) campaign, which offers two advantages over that used in earlier work. First, we utilize the increased signal-to-noise ratio offered by the UDF12 imaging to provide improved measurements for known galaxies at z ≃ 6.5-8 in the HUDF. Second, because the UDF12 data have allowed the construction of the first robust galaxy sample in the HUDF at z > 8, we have been able to extend the measurement of average galaxy size out to higher redshifts. Restricting our measurements to sources detected at >15σ, we confirm earlier indications that the average half-light radii of z ~ 7-12 galaxies are extremely small, 0.3-0.4 kpc, comparable to the sizes of giant molecular associations in local star-forming galaxies. We also confirm that there is a clear trend of decreasing half-light radius with increasing redshift, and provide the first evidence that this trend continues beyond z ≃ 8. Modeling the evolution of the average half-light radius as a power law, ∝(1 + z)^s , we obtain a best-fit index of s = -1.30^(+0.12)_(-0.14) over z ~ 4-12. A clear size-luminosity relation is evident in our dropout samples. This relation can be interpreted in terms of a constant surface density of star formation over a range in luminosity of 0.05-1.0L^*_(z=3). The average star formation surface density in dropout galaxies is 2-3 orders of magnitude lower than that found in extreme starburst galaxies, but is comparable to that seen today in the centers of normal disk galaxies.

We use the UKIDSS Ultra-Deep Survey, the deepest degree-scale near-infrared survey to date, to investigate the clustering of star-forming and passive galaxies to z ~ 3.5. Our new measurements include the first determination of the clustering for passive galaxies at z > 2, which we achieve using a cross-correlation technique. We find that passive galaxies are the most strongly clustered, typically hosted by massive dark matter halos with M_halo > 5 x 10^12 M_sun irrespective of redshift or stellar mass. Our findings are consistent with models in which a critical halo mass determines the transition from star-forming to passive galaxies. Star-forming galaxies show no strong correlation between stellar mass and halo mass, but passive galaxies show evidence for an anti-correlation; low-mass passive galaxies appear, on average, to be located in the most massive halos. These results can be understood if the termination of star formation is most efficient for galaxies of low stellar mass in very dense environments., Accepted for publication in MNRAS. 16 pages, 9 figures, 1 table

We have analysed a sample of 25 extremely red H-[4.5]>4 galaxies, selected using 4.5 micron data from the Spitzer SEDS survey and deep H-band data from the Hubble Space Telescope (HST) CANDELS survey, over ~180 square arcmin of the UKIDSS Ultra Deep Survey (UDS) field. Our aim is to investigate the nature of this rare population of mid-infrared (mid-IR) sources that display such extreme near-to-mid-IR colours. Using up to 17-band photometry (U through 8.0 microns), we have studied in detail their spectral energy distributions, including possible degeneracies in the photometric redshift/internal extinction (zphot-Av) plane. Our sample appears to include sources of very different nature. Between 45% and 75% of them are dust-obscured, massive galaxies at 3300 microJy, which at 35) sources at zphot3 galaxies to be discovered with the future James Webb Space Telescope., Accepted for publication in the ApJL, 6 pages including 1 table and 4 figures. Table 1 has been expanded to provide information for all galaxies in the sample

This paper presents the results from the first wide and deep dual narrow-band survey to select H-alpha (Ha) and [OII] line emitters at z=1.47+-0.02 (using matched narrow-band filters in the H and z' bands), exploiting synergies between the UKIRT and Subaru telescopes. The Ha survey at z=1.47 reaches a flux limit of ~7x10^-17 erg/s/cm^2 and detects ~200 Ha emitters over 0.7deg^2, while the much deeper [OII] survey reaches an effective flux of ~7x10^-18 erg/s/cm^2, detecting ~1400 z=1.47 [OII] emitters in a matched co-moving volume of ~2.5x10^5 Mpc^3. The combined survey results in the identification of 190 simultaneous Ha and [OII] emitters at z=1.47. Ha and [OII] luminosity functions are derived and both are shown to evolve significantly from z~0 in a consistent way. The star formation rate density of the Universe at z=1.47 is evaluated, with the Ha analysis yielding 0.16+-0.05 M_sun/yr/Mpc^3 and the [OII] analysis 0.17+-0.04 M_sun/yr/Mpc^3. The measurements are combined with other studies, providing a self-consistent measurement of the star formation history of the Universe over the last ~11Gyrs. By using a large comparison sample at z~0.1 (from the SDSS), [OII]/Ha line ratios are calibrated as probes of dust-extinction. Ha emitters at z~1.47 show on average 1 mag of extinction at Ha, similar to the SDSS sources at z~0. Although we find that dust extinction correlates with SFR, the relation evolves by about ~0.5 mag from z~1.5 to z~0, with z~0 relations over-predicting the dust extinction corrections at high-z by that amount. Stellar mass is found to be a much more fundamental extinction predictor, with the relation between mass and extinction being valid at both z~0 and z~1.5. Dust extinction corrections as a function of optical colours are also derived, offering simpler mechanisms for estimating extinction in moderately star-forming systems over the last ~9Gyrs [Abridged]., Comment: Accepted for publication in MNRAS. Revised version following the reviewer's report. 21 pages, 23 figures

This paper presents the results from the first wide and deep dual narrow-band survey to select H-alpha (Ha) and [OII] line emitters at z=1.47+-0.02 (using matched narrow-band filters in the H and z' bands), exploiting synergies between the UKIRT and Subaru telescopes. The Ha survey at z=1.47 reaches a flux limit of ~7x10^-17 erg/s/cm^2 and detects ~200 Ha emitters over 0.7deg^2, while the much deeper [OII] survey reaches an effective flux of ~7x10^-18 erg/s/cm^2, detecting ~1400 z=1.47 [OII] emitters in a matched co-moving volume of ~2.5x10^5 Mpc^3. The combined survey results in the identification of 190 simultaneous Ha and [OII] emitters at z=1.47. Ha and [OII] luminosity functions are derived and both are shown to evolve significantly from z~0 in a consistent way. The star formation rate density of the Universe at z=1.47 is evaluated, with the Ha analysis yielding 0.16+-0.05 M_sun/yr/Mpc^3 and the [OII] analysis 0.17+-0.04 M_sun/yr/Mpc^3. The measurements are combined with other studies, providing a self-consistent measurement of the star formation history of the Universe over the last ~11Gyrs. By using a large comparison sample at z~0.1 (from the SDSS), [OII]/Ha line ratios are calibrated as probes of dust-extinction. Ha emitters at z~1.47 show on average 1 mag of extinction at Ha, similar to the SDSS sources at z~0. Although we find that dust extinction correlates with SFR, the relation evolves by about ~0.5 mag from z~1.5 to z~0, with z~0 relations over-predicting the dust extinction corrections at high-z by that amount. Stellar mass is found to be a much more fundamental extinction predictor, with the relation between mass and extinction being valid at both z~0 and z~1.5. Dust extinction corrections as a function of optical colours are also derived, offering simpler mechanisms for estimating extinction in moderately star-forming systems over the last ~9Gyrs [Abridged]., Accepted for publication in MNRAS. Revised version following the reviewer's report. 21 pages, 23 figures

(Abridged) This paper presents an environment and stellar mass study of a large sample of star-forming (SF) galaxies at z=0.84 from the HiZELS survey, over 1.3 deg^2 in the COSMOS and UKIDSS UDS fields. By taking advantage of a truly panoramic coverage, from the field to a rich cluster, it is shown that both mass and environment play crucial roles in determining the properties of SF galaxies. The median specific SFR declines with mass in all environments, and the fraction of galaxies forming stars declines from ~40%, for M~10^10M_sun to effectively zero at M>10^11.5M_sun, confirming that mass-downsizing is generally in place by z~1. The fraction of SF galaxies also falls as a function of local environmental density from ~40% in the field to approaching zero at rich group/cluster densities. When SF does occur in high density regions, it is merger-dominated and, if only non-merging SF galaxies are considered, then the environment and mass trends are even stronger and largely independent, as in the local Universe. The median SFR of SF galaxies is found to increase with density up to intermediate (group or cluster outskirts) densities; this is clearly seen as a change in the faint-end slope of the H-alpha LF from steep (-1.9), in poor fields, to shallow (-1.1) in groups and clusters. Interestingly, the relation between median SFR and environment is only found for low to moderate-mass galaxies (below ~10^10.6M_sun), and is not seen for massive SF galaxies. Overall, these observations provide a detailed view over a sufficiently large range of mass and environment to reconcile previous observational claims: mass is the primary predictor of SF activity at z~1, but the environment, while enhancing the median SFR of (lower-mass) SF galaxies, is ultimately responsible for suppressing SF activity in all galaxies above surface densities of 10-30 Mpc^-2 (groups and clusters)., Accepted for publication in MNRAS, 18 pages, 16 figures, revised version following the reviewer's report

We use the UKIDSS Ultra-Deep Survey to trace the evolution of galaxy clustering to z = 3. Using photometric redshifts derived from data covering the wavelength range 0.3 - 4.5 um we examine this clustering as a function of absolute K-band luminosity, colour and star-formation rate. Comparing the deprojected clustering amplitudes, we find that red galaxies are more strongly clustered than blue galaxies out to at least z = 1.5, irrespective of rest-frame K-band luminosity. We then construct passive and star-forming samples based on stellar age, colour and star-formation histories calculated from the best fitting templates. The clustering strength of star-forming galaxies declines steadily from r_0 ~ 7 h^-1 Mpc at z ~ 2 to r_0 ~ 3 h^-1 Mpc at z ~ 0, while passive galaxies have clustering strengths up to a factor of two higher. Within the passive and star-forming subsamples, however, we find very little dependence of galaxy clustering on K-band luminosity. Galaxy `passivity' appears to be the strongest indicator of clustering strength. We compare these clustering measurements with those predicted for dark matter halos and conclude that passive galaxies typically reside in halos of mass M > 10^13 M_sun while luminous star-forming galaxies occupy halos an order of magnitude less massive over the range 0.5 < z < 1.5. The decline in the clustering strength of star-forming galaxies with decreasing redshift indicates a decline in the hosting halo mass for galaxies of a given luminosity. We find evidence for convergence of clustering in star-forming and passive galaxies around z ~ 2, which is consistent with this being the epoch at which the red sequence of galaxies becomes distinct., Accepted for publication in Monthly Notices of the Royal Astronomical Society. 11 pages containing 8 Figures and 1 table. The source contains additional results tables

We present the largest area survey to date (1.4 deg2) for Lyman-alpha emitters (LAEs) at z~9, as part of the Hi-z Emission Line Survey (HiZELS). The survey, which primarily targets H-alpha emitters at z < 3, uses the Wide Field CAMera on the United Kingdom Infrared Telescope and a custom narrow-band filter in the J band to reach a Lyman-alpha luminosity limit of ~10^43.8 erg/s over a co-moving volume of 1.12x10^6 Mpc^3 at z = 8.96+-0.06. Two candidates were found out of 1517 line emitters, but those were rejected as LAEs after follow-up observations. This improves the limit on the space density of bright Lyman-alpha emitters by 3 orders of magnitude and is consistent with suppression of the bright end of the Lyman-alpha luminosity function beyond z~6. Combined with upper limits from smaller but deeper surveys, this rules out some of the most extreme models for high-redshift Lyman-alpha emitters. The potential contamination of narrow-band Lyman-alpha surveys at z>7 by Galactic brown dwarf stars is also examined, leading to the conclusion that such contamination may well be significant for searches at 7.7 < z < 8.0, 9.1 < z < 9.5 and 11.7 < z < 12.2., To appear in proceedings of "UKIRT at 30: A British Success Story"

The MOONS instrument possesses an exceptional combination of large multiplexing, high sensitivity, broad simultaneous spectral coverage (from optical to near-infrared bands), large patrol area and high fibre density. These properties provide the unprecedented potential of enabling, for the very first time, SDSS-like surveys around Cosmic Noon (z ~ 1–2.5), when the star formation rate in the Universe peaked. The high-quality spectra delivered by MOONS will sample the same nebular and stellar diagnostics observed in extensive surveys of local galaxies, providing an accurate and consistent description of the evolution of various physical properties of galaxies, and hence a solid test of different scenarios of galaxy formation and transformation. Most importantly, by spectroscopically identifying hundreds of thousands of galaxies at high redshift, the MOONS surveys will be capable of determining the environments in which primeval galaxies lived and will reveal how such environments affected galaxy evolution. In this article, we specifically focus on the main Guaranteed Time Observation (GTO) MOONS extragalactic survey, MOONRISE, by providing an overview of its scientific goals and observing strategy., Published in The Messenger vol. 180, pp. 24-29, June 2020.

This White Paper presents the scientific motivations for a multi-object spectrograph (MOS) on the European Extremely Large Telescope (E-ELT). The MOS case draws on all fields of contemporary astronomy, from extra-solar planets, to the study of the halo of the Milky Way and its satellites, and from resolved stellar populations in nearby galaxies out to observations of the earliest 'first-light' structures in the partially-reionised Universe. The material presented here results from thorough discussions within the community over the past four years, building on the past competitive studies to agree a common strategy toward realising a MOS capability on the E-ELT. The cases have been distilled to a set of common requirements which will be used to define the MOSAIC instrument, entailing two observational modes ('high multiplex' and 'high definition'). When combined with the unprecedented sensitivity of the E-ELT, MOSAIC will be the world's leading MOS facility. In analysing the requirements we also identify a high-multiplex MOS for the longer-term plans for the E-ELT, with an even greater multiplex (>1000 targets) to enable studies of large-scale structures in the high-redshift Universe. Following the green light for the construction of the E-ELT the MOS community, structured through the MOSAIC consortium, is eager to realise a MOS on the E-ELT as soon as possible. We argue that several of the most compelling cases for ELT science, in highly competitive areas of modern astronomy, demand such a capability. For example, MOS observations in the early stages of E-ELT operations will be essential for follow-up of sources identified by the James Webb Space Telescope (JWST). In particular, multi-object adaptive optics and accurate sky subtraction with fibres have both recently been demonstrated on sky, making fast-track development of MOSAIC feasible., Significantly expanded and updated version of previous ELT-MOS White Paper, so there is some textual overlap with arXiv:1303.0029

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.