A set of equations linking the time-spread of a laser altimeter echo-profile, commonly known as the pulse-width, to the variance of topography within the pulse-footprint are tested by comparing pulse-width data to surface characteristics measured from high-resolution Digital Terrain Models. The research is motivated by the advent of high-resolution Digital Terrain Models over Mars, which enables the calibration of Mars Orbiter Laser Altimeter pulse-widths, and evolves to include lunar and terrestrial data in an attempt to validate the theory and develop new methods. Analysis of Mars Orbiter Laser Altimeter pulse-width data reveals mixed results. Over homo- geneously rough terrain, at kilometre-scales, these pulse-widths show some correlation to surface characteristics, once poor pulse data has been removed. However, where roughness is highly vari- able over short baselines, little correlation is observed, which is attributed to a mix of georeferencing errors and instrument methods. In a similar study, Lunar Orbiter Laser Altimeter pulse-widths are shown to produce only poor correlations with surface characteristics over local study sites. Instead, the observed correlations differ from orbit to orbit, with the majority of those used appearing to contain poor quality pulse- width data - attributed to the instrument methods - and only 14 % revealing correlations similar, or better, than observed over Mars. Finally, an examination of the relationship between footprint-scale surface characteristics and pulse-width estimates derived from smoothed Ice, Cloud, and land Elevation Satellite echo-profiles enables different pulse-width thresholds to be tested. Here, pulse-widths measured using a 10 % Peak Energy threshold are shown to produce greater correlations than those observed using the Mars Orbiter Laser Altimeter and the Lunar Orbiter Laser Altimeter data, which use a Full Width Half Maximum threshold. To conclude, pulse-widths can show strong correlations to surface roughness and slope within the pulse-footprint. However the assumption that detrended surface roughness can be derived by applying a slope contribution effect is shown to be unfounded. The principal recommendation is for future instruments to use a full echo-profile in estimating pulse-width values at a 10 % Peak Energy threshold, providing both efficient noise removal and a better correlated dataset.

No description available.

The location of Brightest Cluster Galaxies (BCGs), at the centre of the clusters of galaxies, suggests a strong link between the formation and evolution of the BCG and that of the host cluster; with their unique environment distinguishing BCG evolution from that of massive field ellipticals. In this thesis I explore some of the contributing factors to the unique evolution of BCGs. In particular, I investigate the interaction of gas cooling from the intracluster medium (ICM) and the BCG, in fuelling star formation and AGN activity in BCGs, as well as the properties of the multi-phase gas itself. I also investigate the stellar mass growth of BCGs through galaxy--galaxy mergers. I attempt to constrain the prevalence of BCGs undergoing star formation and/or AGN activity by conducting a multi-wavelength photometric census of 981 BCGs, from an X-ray selected sample of clusters at z < 0.5. It is found that at least 14 per cent of the BCGs have colours which deviate from those expected for a passively evolving galaxy. A strong association is discovered between BCG colours and optical line emission, indicating the presence of multi-phase gas and a strong association is also discovered between BCG colour and the X-ray luminosity of the host cluster, with implications regarding the proportion of active BCGs and the selection of a particular sample of clusters. These results demonstrate that a significant fraction of BCGs are in fact active, contrary to their ``red and dead'' reputation. The theme of AGN activity in BCGs is continued via an investigation searching for clusters around some 3500 ROSAT selected AGN. The aim is to address the ambiguity that exists between clusters and AGN in low resolution X-ray imaging, which disfavours the detection of the inherently rare systems where a strong AGN is hosted by a BCG. I identify 22 candidate systems with significant overdensities of red galaxies, with several being independent rediscoveries of such systems. Six best candidate systems are found where the cluster and AGN X-ray emission are likely to be comparable. Identification of such systems will ultimately aid in our understanding of the role of AGN feedback in this unique environment. The stellar mass assembly of BCGs at z < 0.25 is also explored, targeting 23 merger--like BCGs, drawn from a large parent cluster sample, with wide-field integral field spectroscopy. The stellar kinematics are used to determine a bound probability for companion cluster galaxies and average merger timescales are estimated. Due to selection effects the average BCG stellar mass growth cannot be constrained tighter than between 9(+/-3) and 57(+20/-17) per cent, with typical values in the literature of 10-20 per cent. Nevertheless, the techniques utilised in this analysis should help lay the groundwork for subsequent studies; demonstrating the power of using a statistically significant number of IFU observations to study BCG mergers. Spatially resolved optical line emission is also explored in ten cluster cores. A variety of morphologies and kinematic profiles are discovered, and the properties of each individual system are discussed in turn. The most striking results relate to two systems where the ionised gas lies offset from the BCG. An X-ray observation of A2566 confirms the X-ray peak is offset from the BCG and coincident with the offset line emission, which, along with previous observations, suggest cooling of the ICM can occur in isolation of, and away from, the BCG -- likely related to sloshing of the ICM. A 40 kpc filament is discovered in A2533, offset from the BCG and spatially coincident with star formation and dust lane features in the continuum. An ALMA observation also finds cold molecular gas, which almost perfectly traces the warm ionised gas. Without a high resolution X-ray observation a definitive link between the offset emission and the ICM cannot be established for this system, however, we predict the X-ray peak will be offset, analogous to A2566. Such systems allow the rare opportunity of studying cooling flows in isolation of the role of AGN feedback within BCGs.

A number of theories which invoke a general magnetic field in the Galaxy have been proposed in the last ten years, but until recently no attempt has been made to measure the force or flux-density of this field directly. Two separate attempts have been made to measure the magnetic flux-density in five different regions of the Galaxy with the inverse Zeeman effect of hyperfine-structure on the 21-cm hydrogen line. A search was made for circularly polarized radiation on the line edge following a suggestion of Bolton and Wild. The difference in power received between the two opposite senses of polarization was recorded continuously as the receiver scanned in frequency across the line. In the first attempt which is described in Chapter 2, a special receiver and primary-feed were designed, constructed and used with the 250 ft. radio-telescope. The narrow deep Orion-arm absorption-feature in Cassiopeia-A was studied and an upper limit of 5 x la-5 gauss was set on the radial component of flux-density in the absorbing region.

This thesis is concerned with two separate astronomical investigations _ firstly the determination of the line of sight interstellar magnetic field from measurements of the Zeeman splitting of the 21 cm spectral line from interstellar neutral hydrogen clouds, and secondly the search for temporal variations in the emission in the 18 cm spectral lines of' the ground state of' the OH radical from six galactic regions.

In this Thesis we describe the properties of early-type galaxies in the context of hierarchical galaxy formation. We use two variants of the GALFORM model originally introduced by Cole et al.: the Baugh et al. and the Bower et al. models. We test the prescription defined by Cole et al. to calculate the sizes of bulges, by comparing GALFORM predictions with local observational data. We find that the model reproduces successfully several tight correlations observed for early-type galaxies: the relation between velocity dispersion and luminosity, the velocity dispersion-age relation and the Fundamental Plane. However, there is an important disagreement between the models and observations: in the model, the radii of the luminous spheroids are smaller than expected. We analyse how the physical ingredients involved in the calculation of the sizes influence these results. We explore the physics of massive galaxy formation in the models, by predicting the abundance, properties and clustering of luminous red galaxies (LRGs). Without adjusting any parameters in the two models, we find a good agreement between the GALFORM model and observations. We find that model LRGs are mainly elliptical galaxies, with stellar masses around 2 x 10(^11) h-(^1) M(_ʘ) and velocity dispersions of 250 kms-(^1). The models predict the correlation function of LRGs to be a power law down to small scales, which is in excellent agreement with the observational estimates. Finally, we predict the abundance, colour and clustering of submillimeter galaxies (SMGs), which are thought to be the progenitors of local massive early-type galaxies. At the wavelengths where these galaxies are detected, 850 um, the predictions using the standard GALFORM model are inaccurate, hence the time consuming GRASIL code is used in addition to GALFORM. We develop a new method, based on artificial neural networks, to rapidly generate galaxy spectra from a small set of properties.

In this thesis I study the spatial distribution of galaxies, haloes and dark matter particles using a suite of state-of-art cosmological N-body simulations of the growth structure in the Universe. The subjects investigated are conceptually divided into three areas. One line of research, which is made up of Chapters 2 and 3, is to explore the power and limitations of measurements of the imprint of baryonic acoustic oscillations in the clustering of galaxies. I look at how the appearance of the power spectrum is altered by different effects such as nonlinear evolution or redshift space distortions. In these chapters I also explore the best way to analyse survey data and how well new datasets, from both spectroscopic and photometric surveys, will be able to constrain the dark energy equation of state. In a second strand, I study dark matter haloes and their substructures. In Chapter 4， I look at the dependence of the clustering strength of dark haloes on the concentration of the sample. I was able to go beyond the traditional 2-point statistics to extend previous analyses to higher order statistics thanks to the development of a novel way to extract the higher order bias parameters. In Chapter 5, I then zoomed into smaller scales to study a number of properties of the population of substructures within dark haloes. In particular, I consider the mass distribution of substructures as well as their radial distribution and orientation. I also demonstrate that mergers between substructures do indeed occur, which result from objects that are dynamically or geometrically linked before accretion. In the final line of research, presented in Chapters 6 and 7, I develop ideas about how to add more realism to current theoretical predictions for galaxy clustering, and how it would be possible to use low-resolution dark matter simulations to investigate uncertainties in future observations.

In this work we have studied the relationship between the kinematics and shapes of Early Type Galaxies (ETGs) in rich clusters. In particular we were interested to extend the kinematic morphology density relation to the richest clusters. We obtained data from FLAMES/GIRAFFE to probe the stellar kinematics of a sample of 30 ETGs in the massive cluster Abell 1689 at z = 0.183, to classify them as Slow Rotators (SRs) or Fast Rotators (Frs). To date, this is the highest redshift cluster studied in this way. We simulated FLAMES/GIRAFFE observations of the local SAURON galaxies to account for the bias introduced compared to the ATLAS3D sample, which we used as a local comparison. We find that the luminosity function of SRs in Abell 1689 is the same as that in ATLAS3D, down to the faintest objects probed (MK ≈ -23). The number fraction of SRs over the ETG population in Abell 1689 is fSR = 0.15 +/- 0.03, consistent with the value found in the Virgo Cluster. However, within the cluster, fSR rises sharply with the projected number density of galaxies, rising from fSR = 0.01 in the least dense bin to fSR = 0.58 in the densest bin. We conclude that the fraction of SRs is not determined by the local number density of galaxies, but rather by the physical location within the cluster. This might be due to dynamical processes which cause SRs (on average more massive) to sink in the gravitational potential of the cluster. Next we explore the distribution of projected ellipticity ε in galaxies belonging to a sample of clusters from SDSS (z ε = 0.4 (a proxy for FRs) varies from cluster to cluster. We find some significant variations. We go on to probe the projected shape as a function of projected cluster-centric radius. In both samples we find that on average galaxies have progressively rounder projected shapes at lower cluster-centric projected distance. In the SDSS sample we show that this trend exists above and beyond the trend for brighter galaxies to be more common near the centre of clusters (bright galaxies are on average rounder). In order to disentangle the trend for SRs (which are rounder) to be more common near the centre of clusters, we isolate a subsample of FRs only, by considering only galaxies with ε > 0.4. We find that even the intrinsically flat FRs are on average rounder at lower projected cluster-centric distance. We conclude that the observed trend is due either to the dynamic heating of the stellar discs being strongest near the centre of clusters, or due to an anti-correlation of the bulge fractions with the cluster-centric distance.

This research thesis uses multiwavelength observations to investigate a sample of the 3CRR catalogue, as well as a separate radio-loud source, PKS J231O-437, with the general aim of modelling the energy released as synchrotron radiation. The minimum energy magnetic fields are calculated for six of the 3CRR objects, and any correlations between these and source power are discussed in the conclusions. Chapter One introduces active galaxies and jets, explaining what is meant by 'radio-loud', and the classifications used to categorise them, as well as a summary of the characteristics of their host galaxies. It then goes on to cover Unified theories, and how BL Lac objects (one of which, PKS J2310-437, is investigated as a case study) fit into this scheme. The introduction finishes with a section on emission mechanisms, synchrotron radiation, Doppler boosting and minimum energy calculations. Chapter Two is a case study, looking at the BL Lac object, PKS J231O-437. This is a radio and X-ray loud active galaxy which appears to have little optical emission, either nuclear or from jets. ESO NTT and Spitzer data are used to investigate any nuclear or jet flux emitted in five optical and [our infrared bands, with the aim of better categorising this unusual source. Chapters Three and Four are the main body of this research thesis. Using data from Spitzer's lRAC instrument, as well as X-ray and radio data, the underlying electron spectrum of the observed jets is modelled with the aim of discovering the electron spectral break. This is expected to lie in the mid-infrared region; the wavelength range observed by IRAC. This break is then used to calculate the minimum energies and magnetic fields of the jets. Chapter Three covers the observations, data reduction and results, and Chapter Four consists of the data analysis, modelling and discussion of results. Chapter Five concludes the work, summarising the work on the 3CRR sources and PKS J231 0-437, then bringing them together. The chapter finishes with a section on how further investigations could be carried out. The Appendices contain the initial ELLIPSE parameters used for the 3CRR galactic modelling; all of the 3CRR Spitzer images post-galactic subtraction; and three-colour images of the eight sources in which jets were detected, plus one of 3C 231, a starburst galaxy.

This thesis describes the characterisation of non-Gaussianity in the Cosmic Microwave Background (CMB) from observations made with the Very Small Array (VSA) and the Cosmic Background ~mager (CBI). The VSA and the CBI are interferometric instruments designed to image the CMB at angular scales correspondIng to mUltipoles up to .e = 3500. An overview of radio interferometry is given. The experimental challenges related to the obse~vation of the CMB are discussed, and how interferometry is particularly well suited to deal with them. The VSA and the CBI are described. The data reduction processes in both instruments are outlined, as well as the measures adopted to control systematic effects and remove contamination of instrumental and astrophysical origin. The characterisation of non-Gaussianity for this thesis was based on the bispectrum, for which a weighted variance estimator and two normalised estimators were implemented. Null hypothesis tests show that, overall, the VSA data set and the CBI field deep20hr are consistent with Gaussianity. A theoretical bispectrum was used, together with the normalised bispectra estimates from the data to place limits on the non-linear coupling parameter fNL. We combined fNL limits from 32 VSA fields to find a combined limit of IfNLI < 2732. A subset of the VSA data was used to explore the possibility of detecting a bispectrum signal from bright point sources. There is not evidence to suggest that the estimators used in this thesis can be used to detect such signal in the VSA data in a consistent maner. Additions and improvements to the non-Gaussianity tests applied in this work are discussed.