In this thesis I investigate the formation and evolution of the galaxies that eventually form the colour-magnitude relation (CMR) in local galaxy clusters. I survey galaxies that lie on the CMR in nine massive clusters at z~0.2, environments in which the build-up of the faint end of the CMR is still underway. I show that there are relatively few dwarf galaxies on the CMR in the outer, low-density regions of clusters, but that their fraction increases towards higher-density regions as the cluster environment transforms infalling, blue, star-forming galaxies into red, passive, CMR galaxies. However, in the highest density regions, at the very centres of clusters the relative fraction of dwarf galaxies on the CMR is suppressed, evidence that, dwarf galaxies in the highest density regions at z~0.2 are dynamically disrupted. I then use 1.1-mm observations of a massive cluster at z~0.54 to search for active, star-forming cluster galaxies, which would transform into CMR galaxies at lower redshifts as the star-formation terminates. I detect 36 sources in observations of 0.1 deg² of the cluster centre and identify counterparts to ~50% of these submillimetre galaxies (SMGs) using radio, 24-μm and IRAC data. Photometric redshifts suggest that at most two of the SMGs are potential cluster members. If this is the case they each have far-infrared luminosities of ~5x10¹¹ solar luminosities and star-formation rates (SFRs) of ~50 solar masses per year - a significant fraction of the combined SFR of the cluster. I next consider 126 SMGs detected in an 870-μm survey of the Extended Chandra Deep Field South (ECDFS). I derive a photometric redshift distribution of 74 robust radio, 24-μm and IRAC-identified counterparts that peaks at z=2.2. An analysis of sources within the positional error circles of unidentified SMGs identifies a population of likely counterparts with a redshift distribution that peaks at z=2.5±0.3 and likely comprises ~60% of the unidentified SMGs. The remainder are not detected in our IRAC imaging and likely lie at z≳3. In total, I find that ~30% of all SMGs are at z≳3, and the median redshift of all S₈₇₀μm>4 mJy SMGs is z=2.5±0.6. The contribution of SMGs to the global SFRD also peaks at z~2 and SMGs with S₈₇₀μm≳4 mJy and S₈₇₀μm≳1 mJy provide ~5% and ~50% of the global total at z~2, respectively. Analysis of the projected real-space cross-correlation function of SMGs at z=1-3 with IRAC-selected galaxies shows that SMGs are strongly clustered and reside in dark-matter halos of mass (6⁺¹²₋₅)x10¹² solar masses. This halo mass is comparable to that of quasars and the mass at which major mergers are most efficient at triggering starburst activity. I conclude that SMGs at z~2 have star-formation rates, stellar masses and clustering properties that suggests that they are the likely progenitors of the massive CMR galaxies that dominate local clusters.

We use a galaxy formation model to study the nature and evolution of emission line galaxies. In particular, we focus on the properties of Ly-alpha and H-alpha emitters, due to their many cosmological applications being considered for current and future observational studies. By combining a semianalytical model with a large N-body simulation we predict the clustering of Ly-alpha emitters. With increasing redshift, Ly-alpha emitters are found to trace progressively rarer, higher density regions of the Universe. We measure the clustering of Ly-alpha emitters by constructing mock catalogues of surveys finding a good agreement between the model and the observational measurements. Furthermore, we use the mock catalogues to study the sample variance of current and forthcoming Ly-alpha surveys. Current surveys should be extended significantly in solid angle to allow a robust measurement of the clustering of Ly-alpha emitters, particularly at z>8. On the other hand, future space-based galaxy surveys will map the galaxy distribution using H-alpha emitters or H-band selected galaxies at 0.5<z<2 to constrain the nature of the dark energy by measuring the large-scale structure of the Universe. Therefore, we investigate the abundance and clustering of galaxies found using these two selections. H-alpha emitters are found to avoid massive dark matter haloes, whereas H-band selected galaxies are found in the highest mass haloes. By using mock catalogues, we predict the effectiveness of measuring the large scale structure of the Universe for a range of survey configurations using both galaxy selections. Finally, we study the escape of Ly-alpha photons from galaxies using a Monte Carlo radiative transfer code. We simulate galactic outflows in a semianalytical model to study the physical properties of Ly-alpha emitters in a cosmological context. We find that the escape fraction of Ly-alpha emitters can vary greatly depending on the properties of the galaxies, although our results depend on the outflow model used. Our results suggest the need to consider additional physical effects to understand the observed properties of Ly-alpha emitters.

Future galaxy redshift surveys will make high precision measurements of the cosmic expansion history and the growth of structure which will potentially allow us to distinguish between different scenarios for the accelerating expansion of the Universe. In this thesis we study the nonlinear growth of cosmic structure in different dark energy models, using ultra-large volume N-body simulations. We measure key observables such as the growth of large scale structure, the halo mass function and baryonic acoustic oscillations. We study the power spectrum in redshift space in $\Lambda$CDM and quintessence dark energy models and test predictions for the form of the redshift space distortions. An improved model for the redshift space power spectrum, including the non-linear velocity divergence power spectrum, is presented. We have found a density-velocity relation which is cosmology independent and which relates the non-linear velocity divergence spectrum to the non-linear matter power spectrum. We provide a formula which generates the non-linear velocity divergence $P(k)$ at any redshift, using only the non-linear matter power spectrum and the linear growth factor at the desired redshift. We also demonstrate for the first time that competing cosmological models with identical expansion histories - one with a scalar field and the other with a time-dependent change to Newton's gravitational constant - can indeed be distinguished by a measurement of the rate at which structures grow. Our calculations show that linear theory models for the power spectrum in redshift space fail to recover the correct growth rate on surprisingly large scales, leading to catastrophic systematic errors. Improved theoretical models, which have been calibrated against simulations, are needed to exploit the exquisitely accurate clustering measurements expected from future surveys.

In this work we add a Dirac right-handed neutrino superfield to the Minimal Supersymmetric Standard Model (MSSM). We discuss the interactions of the right- handed (RH) sneutrino and its mixing with its left-handed counterpart. We study the possibility of this RH sneutrino to be the lightest supersymmetrie particle (LSP). We obtain that this dark matter candidate is a non-thermal relic, and generally has a small relic density. This we argue makes it an interesting candidate for addressing the Ω(_DM)/ Ω(_b) problem. We then discuss a lepton-number conserving leptogenesis scenario, in which an Affleck-Dine inspired mechanism generates a left-right asymmetry in the sneutrino sector. The left-handed part of this asymmetry eventually genesis mechanism, as the right-handed part of the left-right asymmetry becomes the observed dark matter density.

We investigate improved, more physical methods for modelling key processes in galaxy formation that take place in the interstellar medium, and study their effects on the observed properties and evolution of galaxies. The topics we investigate are: (i) improvements to the relation between the star formation rates (SFRs) and the cold gas contents of galaxies; (ii) how to predict the atomic and molecular gas masses in galaxies with different properties, (iii) how to predict the emission of widely used molecular tracers, such as carbon monoxide (CO); and (iv) the gas outflows from galaxies driven by supernovae and their dependence on local and global properties of galaxies. We perform these studies using the semi-analytic model of galaxy formation GALFORM, and fully embed our calculations in a cosmological scenario, the Lambda cold dark matter paradigm. This is done with the dual aims of understanding how the physical processes above affect galaxy formation and evolution in a statistical fashion, and to improve and extend the predictive power of galaxy formation models. We find that by calculating the SFR from the molecular gas content and relating the molecular-to-atomic mass ratio in the interstellar medium to the hydrostatic pressure in the midplane of the disk, we can explain the observed atomic gas mass function and clustering of galaxies selected by their atomic hydrogen mass, the SFRs of local and high-redshift galaxies, the evolution of the molecular hydrogen gas fraction and the global atomic hydrogen abundance of the universe, and the local scaling relations between gas contents and other galaxy properties. We also find that by coupling GALFORM with a radiative transfer and interstellar chemistry code describing photon dominated regions, our new model can explain the observed emission of CO from different types of galaxy. Finally, based on a physical description of the dynamical evolution of bubbles created by supernovae in the interstellar medium, we find that the outflow rate driven by supernovae depends strongly on the surface density of gas plus stars and the gas fraction. We critically revise the phenomenological prescriptions widely used to describe supernova feedback in the literature and propose new physically motivated prescriptions.

The momentum spectrum and positive-negative ratio of cosmic ray mesons in the near vertical direction at sea- level, have been measured. The statistical accuracy and maximum detectable momentum are higher than have previously been attained by other workers using similar methods. This has been made possible by the modification of a Geiger counter spectrograph and addition of flash-tube arrays. Past particles have been selected electronically, and their trajectories recorded automatically by cameras which photograph the flash-tubes. A precise differential u-meson momentum spectrum has been derived in the momentum range 5 - 1000 GeV/c, after the usual instrumental corrections. In the lower momentum region, 5 - 10 GeV/c, there is good agreement with the spectrum determined with the Geiger counters alone. The measurements in the range 10 - 100 GeV/c are consistent with a T-meson production spectrum of constant exponent, γ = 2.64 ± 0.05. More accurate methods of measurement of the flash-tube data at higher momenta lead to a maximum detectable momentum of the instrument, based on the probable error of deflection measurements, of 657 ± 112 GeV/c. In the momentum range 70 to 700 GeV/c these independent measurements lead to a value of Y = 2,67 ± 0.10 and it must be concluded that there is little change in the exponent of the ₸-meson production spectrum in the whole range of measurement. The positive-negative ratio of μ-mesons at sea- level has been found to increase from about 1.25 at 250 GeV/c to about 1.5 at 250 GeV/c where the results are the first measurement made at such high momenta. The measurements have been used to study the energy loss processes of γ-mesons and also to study the production of ₸-mesons in the primary interactions.

Theories of convection below cloud-base are reviewed, together with experimental techniques and evidence. It is concluded that, over land in sunny weather, a forced convection layer is probably overlain by one in which the heat flux is carried by buoyant plumes which may change their form at a few hundred metres. If space charge is considered as carried by air movement, the convection current i(_2) in forced convection is given by where k is von Karman's constant, z the height, u the mean horizontal wind-speed, and σ the space-charge density. In free convection where h is a number equal to about 0.9, H the heat flux, T the absolute temperature, Cp the specific heat and P the density of air, and g the acceleration due to gravity. Buoyant plumes will probably have space-charge density excesses, of magnitude much less than 1 pC m(^-3). Measurements of space-charge density with filtration apparatus show pulses lasting about 40 s, and about 40 pC m(^-3) high: these seem to be associated with free convection, but are probably not coincident with buoyant elements. The hori2sontal diameters and separations of the pulses are proportional to wind speed. The turbulence theory could be used to determine the charge given to the air by melting ice by measuring the space-charge density gradient over melting snow, A calculation from earlier results gives a charge of about 0.16 uC kgm(^-1) melted, similar to values obtained by other methods. Measurements of potential gradient near a small group of deciduous trees in stormy weather are provisionally explained in terms of point discharge, starting at about 1000 V m(^-1) and reaching 0.5 uA at 1650 V m(^-1). Observations in fog show negative space charge originating at power lines, confirming earlier work, and suggest the use of space charge measurements to study atmospheric diffusion from a point source.

Adaptive Optics (AO) can greatly enhance the resolution of astronomical images, achieving close to diffraction-limited performance in the near infrared; however there are a number of areas where significant improvements can be made, one of them being the very limited field of view that current AO systems can achieve. ‘Wide-field AO’ encompasses those techniques devised to widen the corrected field of view, from a few tens of arcseconds in ‘classical AO’ systems to several arcminutes in Multi-Object AO (MOAO). This thesis researches some topics within ‘wide-field AO’ for astronomy, concentrating its experimental work in some of the key technologies required to implement MOAO: open-loop models to run deformable mirrors (DM) in a MOAO system and a ‘Figure Sensor’ to measure the shape of a DM with required accuracy and at high-speed, in order to incorporate it into the AO control system.

Blazars are the principal extragalactic sources of very high energy gamma-ray emission in the Universe. These objects constitute a sub-class of Active Galactic Nuclei whose emission is dominated by Doppler boosted non-thermal radiation from plasma outflowing at relativistic speeds from the central engine. This plasma outflow happens in the form of large-scale collimated structures called jets, which can extend for Mpc in length and transport energy from the central engine of the galaxy to the larger scale intergalac- tic medium. Over thirty such sources have been discovered to date by ground-based gamma-ray telescopes such as H.E.S.S., and PKS 2155-304 is the prototypical southern-hemisphere representative of this population of objects. In this thesis I have studied in detail some aspects of the temporal variability of the jet emission from PKS 2155-304, combining coordinated observations across the electromagnetic spectrum, from optical polarimetric measurements to X-ray and ground-based gamma-ray data. The temporal properties of the dataset allowed us to derive important physical information about the structure and emission mechanisms of the source and put constraints to the location of the sites of VHE emission and particle acceleration within the jet. We have also derived a sensitive statistical measure, called Kolmogorov distance, which we applied to the large outburst observed from PKS 2155-304 in July 2006, to derive the most stringent constraints to date on limits for the violation of Lorentz invariance induced by quantum-gravity effects from AGN measurements.

The aim of this Thesis is to study the development of pulsar wind nebulae in the TeV regime and in doing so uncover more sources which have as yet not been observed at these wavelengths. It is found that the extent of pulsar wind nebula in the TeV gamma-ray increases with its age while no developmental relationship is seen concerning the luminosity or spectral index of the nebulae when observed in the TeV gamma-ray regime due to uncertainties in the measurements available. TeV gamma-ray upper limits are calculated for several nebulae observed in the X-ray regime allowing the strength of their magnetic fields to be constrained but only one new source, which was previously confused with its companion, was discovered, the Eel Nebula. Predictions of the fluxes of many of the sources for which upper limits are derived in this work have been calculated from observations of their emission in X-rays and some of these sources should be uncovered with the next generation CTA instrument.