The properties of galaxies, such as the galaxy red fraction and galaxy stellar mass function, have been shown to depend upon their environment in the local Universe. Large scale photometric surveys such as the DES and in the future Euclid, will be vital to gain insight into the evolution of galaxy properties and the role of environment through cosmic time. Large samples come at the cost of redshift precision and this affects the measurement of galaxy environment. In this thesis an analysis pipeline is constructed to derive galaxy parameters including absolute magnitudes, stellar masses and galaxy environments. The analysis pipeline consists of well established components, such as HYPERZ, that performs SED fitting and components that I have developed and tested, including codes to compute galaxy environment. Five methods to compute galaxy environment are implemented, including three fixed aperture methods, based on spheres, cylinders and cones, the Nth nearest neighbour method and the adaptive Gaussian method. The codes are optimized and parallelized and are executed on Portsmouth’s high performance computer cluster. The codes are thoroughly tested using mock data. Further testing is conducted employing GAMA data, with an external collaborator. The pipeline is applied to two datasets and the results lead to two scientific papers: Etherington & Thomas (2015) and Etherington et al. (in DES collaboration review). The first study is based on a low redshift sample drawn from the SDSS. Spectroscopic and photometric redshifts and also simulated photometric redshifts with a range of uncertainties are employed to study the impact of photometric redshift uncertainty on measures of environment as a function of the aperture parameters. The photometric environments are found to have a smaller dynamic range compared to the spectroscopic measurements because uncertain redshifts scatter galaxies from dense environments into less dense environments. With the optimal aperture parameter values, even for large redshift uncertainties, ∼ 0.1, there is a Spearman Rank Correlation Coefficient of ∼ 0.4 between the photometric measurements and the spectroscopic benchmark environments. This is sufficient to extract an environment signal from large scale photometric surveys. The second study in this thesis is based on the science verification data from the DES. This is the first set of observations from the survey. This study uses ∼3.2 million galaxies from the SPT-East (South Pole Telescope) field that covers approximately 100 sq. deg. of the sky. From the grizY photometry the analysis pipeline is used to derive galaxy stellar masses and absolute magnitudes. The errors on these properties are assessed using Monte-Carlo simulations sampled from the full photometric redshift probability distributions. Galaxy environments are computed using a fixed conical aperture method, for a range of scales. Galaxy environment probability distribution functions are constructed and the dependence of the environment errors on the aperture parameters is investigated. The environment components of the galaxy stellar mass function for the redshift range: 0.15 < z < 1.05 are calculated. For z < 0.75 it is found that the fraction of massive galaxies is larger in high density environment than low density environments. The low and high density components converge with increasing redshift to z ∼ 1.0 where the shapes of the mass function components are indistinguishable. This redshift is important because it marks the transition between an earlier epoch where the mass distribution of galaxies is independent of environment and a later epoch where the mass distribution does depend on galaxy environment. This study shows the build up of high density structures around massive galaxies, through cosmic time. The results in this thesis demonstrate that large scale photometric surveys can produce competitive galaxy evolution science, enabling further investigations of the role of galaxy environment. This is hugely encouraging for current and future experiments.

This thesis explores the properties of galaxies that reside in regions of high density and the influence of the environment in their evolution. In particular, it aims to shed more light on the understanding of how galaxies stop forming stars, becoming passive objects, and the role played by environment in this process. The work presented here includes the study of the properties of galaxies in clusters at two different stages of their evolution: we first look at cluster galaxies that have recently stopped forming stars, and then we investigate the influence of environment on galaxies while they are still forming stars. The first study is based on Integral Field Spectroscopic (IFS) observations of a sample of disk `k+a' galaxies in a cluster at z~0.3. The `k+a' spectral feature imply a recent suppression of star formation in the galaxies, and therefore the study of their properties is crucial to understanding how the suppression happened. We study the kinematics and spatial distributions of the different stellar populations inhabiting these galaxies. We found that the last stars that were formed (i.e., younger stars) are rotationally-supported and behave similar to the older stars. Moreover, the spatial distribution of the young stars also resembles that of the older stellar populations, although the young stars tend to be more concentrated towards the central regions of the galaxies. These findings indicate that the process responsible for the suppression of the star formation in the cluster disk galaxies had to be gentle, without perturbing significantly the old stellar disks. However, a significant number of galaxies with centrally-concentrated young populations were found to have close companions, therefore implying that galaxy-galaxy interactions might also contribute to the cessation of the star formation. These results provide very valuable information on the putative transformation of star-forming galaxies into passive S0s. We then move to the study of the star formation properties and nuclear activity in galaxies in a multi-cluster system at z~0.165. We employ Tuneable Filter observations to map the Halpha and N[II] emission lines. We show the feasibility and advantages of using these type of observations to map emission lines in a large number of objects at a single redshift, and developed a procedure for the reduction and analysis of the data. We find a large number of optical AGN that were not previously detected as X-ray point sources. The probability that a galaxy hosts an AGN is not found to correlate with environment. From the analysis of the integrated star formation properties of the galaxies in the multi-cluster system we observe a significant number of galaxies with suppressed star formation with respect to the field. Although stellar mass is the main driver of the suppression of star formation, once its effect is removed, we find that galaxies in the core regions have reduced specific star formation rates (SSFRs) with respect to the infall regions. Moreover, the environment influences galaxies differently depending on their stellar mass. Galaxies with low masses experience a change in morphology (from irregulars and spirals to early-types) and colour (blue to red) as they fall into regions of higher density. However, many massive spiral galaxies retain their disk morphologies and the visibility of their spiral arms all the way to the core regions. Before becoming passive, these galaxies experience a phase exhibiting red colours and relatively high SSFRs. A significant fraction of the spiral galaxies with relatively high masses go through this phase, which could represent the transition towards becoming S0s. We finish by presenting some interesting results on the spatial distribution of the emission-line regions in the cluster galaxies. We develop a method to create emission-line images, which successfully preserves the flux within the emission lines. Our analysis on the concentrations and sizes of the star-forming regions shows that the star-forming regions of cluster galaxies are generally more concentrated than the underlying stellar populations. However, we find no differences in the spatial distribution of the star formation between galaxies in the infall and in the core regions, but the star formation is more concentrated than in the field galaxies studied in previous works. These results imply that the process responsible for the concentration or truncation of the star formation in the galaxies took place before entering the multi-cluster system of our study.

The structural evolution of cosmic dust analogues has been investigated using in situ synchrotron X-ray powder diffraction (SXPD) at the Diamond Light Source. Amorphous Mg/Ca silicates are produced as analogues of cosmic dust using a modified sol-gel method. They are studied under non-ambient temperature and pressure conditions using in situ powder diffraction, complemented by FTIR and Raman spectroscopy. The solid-state mineralisation of amorphous grains is observed by thermal annealing and the results of this allow the environmental conditions leading to the formation of crystalline dust grains in astrophysical environments to be constrained. The solid-gas carbonation of amorphous Ca-rich silicates is studied using in situ SXPD and analysed using full-profile fitting techniques, while the effect of ex situ carbonation on the short range ordering of amorphous grains is investigated using high energy SXPD and Pair Distribution Function (PDF) analysis. The formation of a metastable calcium carbonate phase (vaterite) is observed and the importance of this in relation to astrophysical environments is discussed. In situ Raman and SXPD data of CO2 clathrate hydrates are presented and the importance of the Raman data obtained here with relevance to future remote sensing missions to Solar System bodies is discussed. This work indicates the importance of laboratory work to the field of astrophysics and provides novel experimental approaches to aid our understanding of astrophysical processes.

This thesis explores the growth of galaxies during the first few billion years of galaxy formation and their potential role as the sources which powered the process of reionization. The data used throughout the thesis is taken from the Cosmic Assembly Near-infrared Extragalactic Legacy Survey (CANDELS). First, we measure new estimates for the galaxy stellar mass function and star formation rates for samples of galaxies at z ~ 4, 5, 6 &7 using data in the CANDELS GOODS South field. The deep near-infrared observations allow us to construct the stellar mass function at z > 6 directly for the first time. We estimate stellar masses for our sample by fitting the observed spectral energy distributions with synthetic stellar populations, including the contributions from nebular line and continuum emission. The observed UV luminosity functions for the samples are consistent with previous observations, however we find that the observed M(UV) - stellar mass relation has a shallow slope more consistent with a constant mass to light ratio and a normalisation which evolves with redshift. We observe stellar mass functions which have steep low-mass slopes (alpha ~ -1.9), steeper than previously observed at these redshifts and closer to that of the UV luminosity function. Integrating our new mass functions, we find the observed stellar mass density evolves from log10(rho) = 6.64 +0.58/-0.89 at z ~ 7 to 7.36 +/- 0.06 solar masses per Mpc^-3 at z ~ 4. Combining the measured UV continuum slopes (beta) with their rest-frame UV luminosities, we calculate dust corrected star-formation rates (SFR) for our sample. We find the specific star-formation rate for a fixed stellar mass increases with redshift whilst the global SFR density falls rapidly over this period. Our new SFR density estimates are higher than previously observed at this redshift. Next, we utilise the same dataset to test a new method for estimating the merger fraction of galaxies in photometric surveys. Using a probabilistic method for estimating close galaxy pairs using photometric redshift probability distributions, we estimate the merger fraction of galaxies at z > 2. For projected separations of 5 <= r <= 20 kpc and 5 <= r <= 30 kpc we measure the merger fraction for mass selected samples of log(M) > 9.5 and log(M)> 10 and merger ratios of 1:4 or less (major mergers). For assumed merger timescales based on hydrodynamical simulations, we estimate the average time between mergers per galaxy (Gamma, Gyr) and the comoving merger rate (R, /Gyr/Mpc^-3). Over the redshift range 2 < z < 4 we find that the average time between mergers per galaxy is approximately constant. Compared to the star-formation rates measured for galaxies at these masses, we conclude that star-formation is the dominant form of growth (by a factor ~10 times) during this epoch. Although we find that the methodology performs well at z ~ 4, more data is required to make robust estimations of the merger fraction at z ~5 or z ~ 6. Similarly, tighter constraints on the observed stellar mass functions are required before we can draw meaningful conclusions from the observed comoving merger rates. Finally, we present a new analysis of the ionizing emissivity (N_ion, /s/Mpc^-3 for galaxies during the epoch of reionization and their potential for completing and maintaining reionization. We use extensive SED modelling -- incorporating two plausible mechanisms for the escape of Lyman continuum photon -- to explore the range and evolution of ionizing efficiencies consistent with new results on galaxy colours (beta) during this epoch. We estimate N_ion for the latest observations of the luminosity and star-formation rate density at z < 10, outlining the range of emissivity histories consistent with our new model. Given the growing observational evidence for a UV colour-magnitude relation in high-redshift galaxies, we find that for any plausible evolution in galaxy properties, red (brighter) galaxies are less efficient at producing ionizing photons than their blue (fainter) counterparts. The assumption of a redshift and luminosity evolution in beta leads to two important conclusions. Firstly, the ionizing efficiency of galaxies naturally increases with redshift. Secondly, for a luminosity dependent ionizing efficiency, we find that galaxies down to a rest-frame magnitude of M_uv ~ -15 alone can potentially produce sufficient numbers of ionizing photons to maintain reionization as early as z ~ 8 for a clumping factor of C = 3.

Galaxy formation is still a current topic in astronomy. An important tool to understanding it is through simulation, which allows galaxies to be studied from all angles and across time. It allows us to explore the gap between observation and theory, but only if the results are sufficiently accurate. In this thesis I look at the majority of the simulation pipeline from running through the various stages of analysis, and some of the limits of their accuracy, and the fidelity of the subsequent analysis tools. It starts by looking at running simulations from initial conditions, and what influence changing parameters and simulation engines has on the outcome. Then I look in detail at how successful subhalo detection is by comparing a number of substructure finders, and examining their strengths and weaknesses. Following this I focus on a single parameter recovered for such haloes, the spin, and how well it was recovered, and what it tells us about the spin of substructures. Following this I investigated the building of merger trees, by writing my own merger tree program, and comparing it with some of the established ones. Then I look at using these processes as input to semi-analytic models, and how mass changes could affect the outcome. Finally I used a number of these tools to investigate the fate of some of the larger haloes formed at early times in an attempt to show where ultra-compact dwarf galaxies are formed and their fate.

In this thesis we investigate the evolution of galaxies since z = 3. There are several methods to measure the star formation rate (SFR) of galaxies, they all however have drawbacks. Several studies have investigated the SFR at high redshifts using SFR trac­ers that suffer from uncertainties, either from the tracer used, or from the uncertainties correcting for the effects of dust. We have new measurements of the Ha emission line for a sample of galaxies at =~1; Ha is a more accurate SFR-tracer than other com­monly used tracers, but until now had been technically difficult to measure at : > 0.85. We investigate methods to correct these observations for dust and we use these mea­surements to investigate the relation between SFR, stellar mass and colour. We find that there is a drop in the fraction of massive (M, > 1011 M.) star-forming galaxies at = < 0.9 and that the fraction of all galaxies that are star-forming drops steadily and significantly with redder (U — B) colours. We find that the M„-SFR (galaxy main sequence, GMS) is flatter than previously measured and that for the most massive galaxies, star formation shuts off abruptly at =~1.

The main aim of this thesis is to understand and investigate some essential phys- ical processes leading to dust grain growth and their interactions in plasmas. This is achieved by applying both analytic and numerical models. Three main situations are explored: dust grains growth in presence of electrostatic and electromagnetic fields, dust grains interaction in submicron scales, and collective effects of dust grains above thundercloud. The evolution and character of plasma dust has wide-ranging implications for astro- physics and laboratory plasmas, including plasma processes and fusion devices. The local electromagnetic fields can influence the conditions for dust growth, leading in some cases to naturally occurring prolate-spheroidal dust shapes. However, presence of magnetic fields can have significant effects on dust growth. Results for dust growth by ion accretion under the combined influence of an applied magnetic field and the evolving electrostatic field arising from the charged grain in 1D and 3D have been presented. The calculations show that most ions starting near the grain surface ulti- mately collide with it, while those starting further away execute orbital motion around the magnetic field lines and drift toward the grain. Moreover, the energy spectrum for impacting ions shows discrete structure in presence of a parallel oriented magnetic field. Finally, we note that the magnetic field influences the spatial deposition pattern of ions, leading to increasing ions fluxes at the grain ends. Microdischarge plasmas is an electrical discharges which occurs in geometries in range of sub-millimetre length scales. However, a much extreme situation than mi- crodischarge plasma where small size charged dust grains can cause breakdown for the neutral gas when dust inter space reach to sub-micro scales. The interactions of charged dust grains in plasma where molecules of Oxygen gas are present and the ef- fect on the discharge of the ambient gas is investigated in presence of magnetic field. The particle in cell model was used to simulate electrons motion in addition to using Monte Carlo method to simulate the electrons collisions with neutrals. The importance of the magnetic field was explored by varying the parameter (p) which gives the rela- tive size of the electric field to the magnetic field. The distribution of electrons kinetic energies was investigated in two cases when (p = 103) and (p = 102). At the first case the gained energy increased dramatically, however, the gained energy did not ex- ceed further than the metastables threshold as a result of consuming electrons energy in metastable collisions. When magnetic field is increased (p = 102), gained energy is fluctuated as a results of contribution in gyromotion orbits and electrons only involved in metastable collisions. However, a number of metastable in this case is lower than (p = 103) case. The electron beam can occur just after sprites. The presence of charged dust above thundercloud are thought to have a basic role in the electron beam formation in which the electrons avalanche in sprite event leaving an environment of negative charged dust and positive ions. This environment was simulated in a model like hollow cathode with a column of positive ions inside. The particle in cell method was used to simulate particles motion. Results for electrons evolution in such this environment with and without presence of positive ions were presented. Electrons in environment without positive ions evolve upwards gaining lower final energy. For the case when positive column is presented, electrons evolve upwards in a long path and do not biased to sidewalls. The trajectory of the electron shows an oscillator motion. The period of such motion depends on the electron’s original position. Electrons gain higher energy in a shorter time comparing to the case when the ions column is not simulated.

The majority of matter in the Universe is dark. World wide efforts to understand this dark component of the Universe are underway and the current evidence suggests the existence of a non-relativistic, non-baryonic and weakly interacting massive particle (WIMP). This weakly interacting dark matter should occasionally couple to baryonic matter, primarily through nuclear interactions. The predicted event rates are low (< O(1) events/kg/day). The energy deposited is also expected to be low (<~ 50 keV), and so distinguishing a WIMP signal above the radioactive and cosmic backgrounds is a difficult challenge. The ZEPLIN{III device was designed to meet this challenge and achieve a competitive sensitivity to WIMP-nucleon interactions. The ZEPLIN{III detector is a two phase time projection chamber using liquid xenon as a target. The instrument was designed to detect dark matter by measuring scintillation and ionisation. Measuring two signals produced by incident radiation allows for discrimination between event types. This allows separation of the main component of the background radiation (primarily electron recoils) from any population of WIMP events that may be present in the data. The ZEPLIN-III detector completed its first science run in 2008, achieving a discrimination power of 1:7800 between nuclear and electron recoils, the highest of any liquid xenon detector. This result limited the WIMP-nucleon cross section to less than 8:4 X 10-8 pb at 90% confidence level (double sided) for a WIMP mass of 55 GeV/c2. The ZEPLIN-III detector then entered an upgrade phase. The two main improvements included the installation of a new ultra-low background PMT array, significantly reducing the main source of background events, and the addition of a veto detector. The veto detector significantly increased the detector's ability to reject WIMP-like background signals, which may be produced by background neutron events. The veto detector also aided background discrimination by detecting 28% of γ-ray events from the fiducial volume of ZEPLIN-III. The second science run of ZEPLIN-III began in June 2010 and continued until May 2011. During the second science run the discrimination power was 1:280 between nuclear and electron recoils. A total of 8 events were observed in the WIMP search region, which is consistent with background expectations. Assuming a null detection allowed the exclusion of the scalar cross-section above 4:8 10-8 pb near a WIMP mass of 51 GeV/c2. This result was combined with the result from a re-analysis of the first science run using more recent results for the relative scintillation yield, Leff, to give a total limit on the spin independent cross-section of 3:9 X 10-8 pb at 90% confidence near 52 GeV/c2 WIMP mass for the ZEPLIN-III experiment. The WIMP-neutron spin-dependent cross-section limit is 8:0 X 10-3 pb at 50 GeV/c2 at 90% confidence for the combined first and second science runs. At the time of publication, these were the world's second best, and best results, respectively.

This work investigates the properties of Early-Type Galaxies (ETGs; elliptical and lenticulars) containing thermal dust emission, with aims of linking the formation and evolution of these galaxies with their current dust properties. Three different proxies for morphology are considered for selecting ETGs, and these are tested against three sets of visually classified galaxies. We find that classifying ETGs as those galaxies in the optical Red Sequence results in samples with ≳35% contamination by late-types, and ≲82% completeness. Concentration and Sérsic index proxies result in slightly improved contamination levels of ≳30% and ~60-70% completeness. These results lead to the conclusion that morphological proxies cannot be used to create fully robust samples of ETGs. Therefore, we choose to use visual inspection to identify ETGs at low redshifts.

Stellar feedback processes have been suggested as a mechanism for explaining various properties of galaxies, especially dwarf galaxies, which have weaker potentials and thus lower escape velocities for galactic winds. In this thesis, I present work done during my DPhil to better understand these processes. I begin by discussing the techniques used to simulate galaxies as collections of astrophysical fluids in a cosmolog- ical context, and present some methods for interpreting the results of such simulations. I then present two projects aimed at furthering our understanding of feedback in dwarf galaxies. The first project is the investigation of a suite of simulations of satellites of a Milky Way-class halo. We discuss the formation of high-redshift dwarf galaxies and the effect that supernova feedback and reionisation have on the gas content and star formation history of these objects. We find that neither process has a dramatic effect on the star formation rates in high redshift dwarf galaxies that have already begun forming stars prior to reionisation. We do find, however, that the population of satellites is dramatically altered by the presence of cooled gas in the host halo, which increases the tidal stripping of satellites that pass close to the host. The second project concerns detailed simulations of a 15 solar mass star throughout its evolution, studying photoionisation, wind and supernova feedback from this star in various environments. Preliminary results are given for these simulations, which are compared to the results of previous authors.