This thesis studies how the morphologies of a large sample of clusters of galaxies can be used to constrain models of the dynamical evolution of the cluster, the evolution of the cluster galaxies, and the underlying cosmological scenario. Chapter 1 gives the introduction to this thesis and Chapter 2 describes the ROSAT PSPC instrumentation together with the data analysis techniques used. In Chapter 3, the morphology of each cluster is found using isophotal shape analysis on the smoothed image. The morphology is parameterised by the axial ratio, centroid variation and radial fall-off parameter (). The distributions of these parameters for the sample are compared with those predicted by N-body simulations from Mohr et al. (1995) using three different cosmologies. The results from this comparison favour high- cosmologies (i.e., closed universe), with a degree of galactic wind injection into the Intra-Cluster-Medium. However, it should be stressed that the parameters used in the low- simulations are likely to have enhanced the discrepancy between the sample data and the low- models, leading to a biased result. In Chapter 4, the morphology of each cluster is found using radial surface brightness profile fitting, yielding best-fit values for the core radius, and . The correlations of these parameters and other X-ray (e.g. luminosity, temperature) and optical (e.g. galaxy velocity dispersion) parameters are compared to results from previous studies. Analytical models by David et al. (1991b) for the interaction between evolving galaxies and the ICM using a range of Initial Mass Function exponents (x) for the evolving galaxies are also investigated. These comparisons indicate that the most likely scenario is one with an IMF exponent of ~ 1, with galactic winds enriching the energy and Iron content of the ICM.

We present the results of several investigations into the nature of Narrow Line Seyfert 1 Galaxies (NLS1s). These investigations comprise optical spectroscopy, with particular attention paid to the Coronal Line Region (CLR), short term monitoring in the B band, and a search for optically thin gas in the Broad Line Region of AGN. Optical spectra have been obtained for 19 NLS1s. A large database of spectral features is presented, including upper limits for coronal lines when 3 detections were not obtained. These will provide a valuable resource for testing models of the EUV continuum. There is some evidence of broad wings to H in NLS1s. The Narrow Line Region shows evidence of high electron temperatures and low electron densities. The Coronal Line Region consists of gas in a decelerating outflow. No simple relation between coronal line strengths and the ROSAT PSPC photon index is seen. NLS1s do not show evidence of variability in the B band over timescales of 1 week. The B band continuum appears not to share a common origin with the highly variable soft X-ray flux. The O I 8446 line is systematically narrower and more asymmetric than H in AGN generally. The difference in FWHM becomes more pronounced with decreasing line width. This indicates that optically thin gas is present in the BLR, and is a more important component of it in NLS1s, where it extends closer to the core of the line. These results favour models in which NLS1s are characterized by a relatively high accretion rate onto a relatively small black hole. They also imply the presence of a highly ionized, optically thin inner BLR and a less highly ionized, optically thick outer BLR. The strong soft excess in NLS1s causes the inner BLR to extend further outwards than in 'normal' Seyfert 1s.

Our understanding of the soft X-ray properties of nearby galaxies has been revolutionised as a result of the Rontgensatellit (ROSAT) mission. This thesis considers a number of aspects of the properties of nearby galaxies on the basis of recent ROSAT PSPC and HRI observations. Firstly, the extragalactic contribution to the X-ray background in the softest accessible X- ray band (0.1 - 0.4 keV) is investigated using the shadows cast by the H I discs of nearby galaxies. A preliminary investigation considers the case of NGC 55, a nearby edge-on galaxy with an extensive H I disc. The technique is then refined and employed on a sample of nearby galaxies, resulting in the best constrained measurement currently available of the extragalactic X-ray background intensity at 0.25 keV of 24.9 5.0 keV cm-2 s-1 sr_1 keV-1. This result has implications for the source populations which compose the extragalactic X-ray background below 1 keV. Detailed studies of the X-ray properties of two nearby galaxies, NGC 55 and NGC 4736, are then presented. The X-ray emission from NGC 55 is dominated by a population of point sources, with some diffuse emission evident in and around its disc. NGC 4736, on the other hand, is dominated by the emission from an extended nuclear source. X-ray data strongly suggests that this region contains a low-luminosity AGN, a conclusion that is supported by observations at other wavelengths. The incidence of low-luminosity AGN in nearby galaxies is probed by correlating ROSATPSPC point source catalogues with an optically-identified sample of nearby galactic nuclei. A sample of 90 "nuclear X-ray sources" is defined, and general trends in their X-ray properties are identified for example, low-luminosity Seyfert nuclei are generally much more X-ray luminous than nuclear H II regions, and soft X-ray hardness ratios are seen to differentiate between optical broad-line and narrow-line AGN.

This thesis discusses the origin of the broad emission lines seen in active galactic nuclei (AGN), in the context of a disc-wind model. An out-flowing nuclear wind generates Kelvin-Helmholtz instabilities within the atmosphere of an accretion disc, which surrounds a super-massive (~ 3 x 10 7 M⊙ ) black hole. The broad line region (BLR) clouds are a direct result of this interaction. The BLR clouds reach velocities required to explain the broad-bases of the permitted lines, within a few sound crossing times, and are destroyed on a similar time scale. We examine NGC5548, and NGC4151 in detail, and conclude that both sources have a small inner BLR radius (1016 cm). By using near simultaneous CIV and Hbeta profiles of NGC.5.548 it is possible to examine the optical and UV spectral regions simultaneously. Observed continuum light curves were used to predict line light curves. Comparisons with observation indicate that the inner and outer BLR radius, ionisation parameter, column and particle density, for both sources are plausible. I examine NGC4151 in detail, particularly the CIV line. The line probably comprises more components than the simpler configuration in NGC5548. For example, reflection of CIV line photons off of a surface subtending a solid angle larger than 2pi, can explain the excess flux in the long-wavelength side of the line, and why this is seen to respond before the short-wavelength side, without invoking in-falling clouds. It is possible to rule out the BLR clouds as directly responsible for the UV absorption. However, the cloud-wind interaction is shown to provide a source of highly ionised, low-column density material, that could be the source of UV absorption. This material covers a large solid angle, which implies that a significant fraction (~ 30%) of Seyfert-1s should show an absorbing component.

Signatures of dark matter can be manifold. In the framework of weakly interacting massive particles they can come from annihilations in dark matter rich regions, from collisions of dark matter particles in terrestrial direct search experiments or from production of dark matter at particle accelerators. This thesis focuses on the latter two possibilities. In the context of collider signatures, we discuss how deviations from background expectations can be interpreted in dark matter models. We look at two examples. First, we see how anomalies in searches for Supersymmetry point towards specic mass spectra in the Minimal Supersymmetric Standard Model (MSSM) at the example of a slight dilepton excess observed by CMS. These spectra are then constrained further by taking complementary analyses into account via a recasting of their limits. This recasting is necessary, because limits on the MSSM spectrum are strongly model dependent. Second, we investigate how deviations in the Higgs to diphoton decay rate can be explained by new vector-like leptons. As we will show, this model not only provides a valid dark matter candidate, but simultaneously leads to a strong rst order electroweak phase transition that is necessary for the generation of the observed baryon asymmetry in electroweak baryogenesis scenarios. Future direct dark matter experiments will be challenged by an irreducible background coming from coherent neutrino-nucleus elastic scattering events that mimic dark matter collisions. This creates a lower limit on accessible dark matter-nucleon cross sections. We show that information coming from the direction of the recoiling nucleus can serve as a strong discriminator between neutrino and dark matter events such that this neutrino bound can be avoided. Necessary exposures of directional searches to surpass this limit are computed.

Determining the nature of dark matter (DM) remains one of the key challenges in both particle physics and cosmology. Although we know the approximate distribution of DM in the Universe, we lack an understanding of its fundamental properties such as its mass and potential couplings to Standard Model particles. In the weakly-interacting massive particle (WIMP) paradigm, DM was in thermal equilibrium in the early Universe and we should expect scattering to have occurred between DM and Standard Model particles. In this thesis, we first consider the impact of primordial scattering between DM and radiation (photons or neutrinos). Such interactions give rise to a modification in the amplitude and position of the cosmic microwave background (CMB) acoustic peaks and a series of damped oscillations in the matter power spectrum. We obtain constraints from the Planck satellite and other CMB experiments, and then derive limits from large-scale structure (LSS) surveys. By providing forecasts for future experiments, we illustrate the power of LSS surveys in probing deviations from the standard cold DM (CDM) model. Then, using high-resolution N-body simulations, we show that the suppressed matter power spectra in such interacting DM scenarios allows one to alleviate the small-scale challenges faced by CDM; in particular, the "missing satellite" and "too big to fail" problems. Finally, we show that the excess of 511 keV gamma-rays from the Galactic centre, which has been observed by numerous experiments for four decades, cannot be explained via annihilations of light WIMPs, suggesting an astrophysical or more exotic DM source of the signal.

Thin film growth and desorption behaviour of simple molecules have been studied by means of surface science techniques, such as mass spectrometry and reflectionabsorption infrared spectroscopy (RAIRS), in order to understand the physiochemical processes and intermolecular interactions in model interstellar ices. The systems of interest comprise a silica surface, representing the bare grains in the interstellar medium, and films of water (H2O), methanol (CH3OH), diethyl ether ((CH3CH2)2O) and benzene (C6H6). While H2O and CH3OH are key components of the icy mantles, (CH3CH2)2O and C6H6 are found in lower abundances being two products, among many, of the rich chemistry occurring in these environments. Temperature programmed desorption and IR signatures of pure solid H2O, CH3OH, and (CH3CH2)2O adsorbed on amorphous silica were compared as a function of surface coverage and temperature. H2O and (CH3 CH2)2O display opposite behaviours, consistent with two-dimensional island formation and wetting of the amorphous silica surface respectively. CH3OH, being intermediate between the two species, exhibited aspects of both behaviours. Temperature programmed RAIRS has revealed evidence for thermal activation of di↵usion of H2O over the amorphous silica surface between 40 K and 60 K, and of CH3OH between 20 K and 40 K, while no conclusive evidence was found for such with (CH3CH2)2O. Experiments have been performed to study the thermal desorption and the IR features of C6H6 on CH3OH and (CH3CH2)2O solids in comparison to those on a solid H2O substrate at 110 K. The results give a clear picture of the C6H6 film growth from low to high coverages. Ab initio quantum chemical calculations highlight the key interactions between the two species for each system, C6H6/H2O, C6H6/CH3OH and C6H6/(CH3CH2)2O, in support of the interpretation of the data. Building on this basis, 250 eV electron irradiation of C6H6 on thick ices of H2O, or CH3OH, or (CH3CH2)2O was investigated to demonstrate the crucial role of hydrogen-bonding in propagating electronic excitation to the solid-vacuum interface where C6H6 desorption can occur. Competitive electron-induced chemistry in the form of molecular hydrogen (H2) formation was also observed. The electron beam used in the these experiments is inelastically scattered by the molecules in the solid ices forming a similar flux of electrons to that associated to cosmic rays. Conclusions related to the impact of these observations on the early phase of icy interstellar grain chemistry are discussed.

Our aim in this thesis is to measure the dependence of quasar clustering with redshift and luminosity. We employ the two-point correlation function to measure the clustering of quasars and compare our results to models of quasar activity. Firstly, we present the photometry of the VST-ATLAS survey. This survey aims to image 4700 deg2 of the Southern Sky to approximately the same depth as SDSS with the second data release covering 60% of the planned survey. The VST-ATLAS median ‘seeing’ is on average 0.4'' less than that of SDSS images and the median point-source depth is on average 0.4mag fainter. The r-band has 0.9'' median seeing (cf. 1.24'' in SDSS) and median 5s depth for point-sources of 22.67 [AB] (cf. 22.31 [AB] in SDSS). The use of gri imaging from the AAVSO Photometric All-Sky Survey has been used to improve the accuracy of the zero-point calibration such that VST-ATLAS photometry agrees with SDSS to the 0.02mag level. We verify the CASU generated catalogue parameters such as the morphological classifications, aperture fluxes and aperture magnitude corrections against the SDSS and we demonstrate that the flat fielding and scattered light correction result in photometry uniform to 0.006mag. We go on to present a new redshift survey, the 2dF Quasar Dark Energy Survey pilot (2QDESp), which consists of 10000 quasars from 150 deg2 of the Southern Sky, based on VST-ATLAS imaging and 2dF/AAOmega spectroscopy. Combining our optical photometry with the WISE (W1,W2) bands we can select essentially contamination free quasar samples with 0.8 < z < 2.5 and g < 20.5. At fainter magnitudes, optical UVX selection is still required to reach our g~22.5 limit. Using both these techniques we observed quasar redshifts at sky densities up to 90 deg-2. Further, we use the two-point correlation function to measure the clustering of quasars. By comparing 2QDESp with other surveys (SDSS, 2QZ and 2SLAQ) we find that quasar clustering is approximately luminosity independent, with results for all four surveys consistent with a correlation scale of r0=6.1+/-0.1 h-1 Mpc, despite their decade range in luminosity. We find a significant redshift dependence of the correlation scale, particularly when BOSS data with r0=7.3+/-0.1 h-1Mpc are included at z~2.4. All quasars remain consistent with having a single host halo mass of 2+/-1 x10^12 h^-1 M. This result implies that either quasars do not radiate at a fixed fraction of the Eddington luminosity or AGN black hole and dark matter halo masses are weakly correlated. No significant evidence is found to support fainter, X-ray selected quasars at low redshift having larger halo masses as predicted by the ‘hot halo’ mode AGN model of Fanidakis et al. (2013). Finally, although the combined quasar sample reaches an effective volume as large as that of the original SDSS LRG sample, we do not detect the Baryonic Acoustic Oscillation (BAO) feature in these data.

This thesis was triggered by the question what is the nature of the sources producing the bulk of the X-ray background at hard energies. Of course the pre-Chandra missions did not allow any definite answer to this question. Therefore the approach adopted in this work is to examine whether candidate populations of objects could contribute to the X-ray background significantly. This was achieved by studying spectroscopically a variety of objects. To be more specific, in Chapter 3 it was examined whether broad line quasars, which produce the bulk of the X-ray background at soft energies, contribute significantly to the hard X-ray background as well. In Chapter 4 the X-ray properties of a sample of Seyfert 2 galaxies were examined. The results were examined in the light of the current X-ray background synthesis models. This study revealed two "odd" Seyfert 2 galaxies (NGC3147 and NGC4698). Odd, in the sense that although both galaxies are classified as Seyfert 2 in the optical, their X-ray data do not show evidence for absorption above the Galactic. Possible scenarios explaining the emission from the two galaxies are examined in Chapter 5. Chapter 6 considers the spectral properties of the Ultraluminous infrared galaxy 'The Superantennae'. In Chapter 7 a study of the composite galaxy Mrk609 is presented. The composite galaxies resemble the narrow-line X-ray galaxies (NLXGs) detected in large numbers in deep ROSAT surveys. Thus the study of the spectra of composite galaxies provides an indirect insight into the spectra of the NLXGs. Finally Chapter 8 summarises the results of this work.

This thesis presents results from a sample of quasars observed with the X-ray astronomy satellite ASCA. The ASCA sample consists of 68 quasars, 35 of which are radio-loud and 33 radio-quiet, covering a range of quasar redshift and luminosity. Differences were found between the radio-loud and radio-quiet quasars; the radio-loud quasars tend to have harder (or flatter) X-ray spectra (~1.5-1.6) and are more X-ray luminous, compared to the softer (~1.9), lower luminosity, radio-quiet quasars. In addition it is found that the line or reflection component observed in some of the radio-quiet quasars is diminished (or absent) in the radio-loud quasars. These observations are consistent with a Doppler-boosted component from a relativistic jet being present in the radio-loud quasars, but not the radio-quiet quasars. Evidence for reprocessing of the primary X-ray emission is also seen in several quasars. Iron line and reflection features are found predominantly in the radio-quiet quasars. The rest energy and ionisation state of the line emission was found to increase towards the higher luminosity quasars; this was interpreted in terms of the increased ionisation of the inner accretion disk with luminosity and accretion rate. Indeed the highest luminosity radio-quiet quasars show no line or disk reflection features, the result being a featureless power-law continuum, which can be explained if the quasars accrete near the Eddington limit. X-ray absorption is also found in several of the quasars; a trend is found for the absorber column density to increase with quasar redshift. When corrected for calibration effects and local origins, this absorbing material must either reside locally to the quasars or originate from line-of-sight matter.