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The presence of massive objects is detectable in observations via the gravitational lensing effect on light from more distant sources. From this effect it is possible to reconstruct the masses of clusters, and the distribution of matter within the cluster. However, further theoretical work needs to be done to properly contextualize any proposed projects involving, for instance, SALT data sets. Observational lensing studies use one of two techniques to recover the lens mass distribution: parametric (model dependent) techniques; and, a more recent innovation, non-parametric methods. The latter deserves further study as a tool for cluster surveys. To this end, we provide a comprehensive analysis of existing non-parametric algorithms and software, as well as estimates on the likely errors to be expected when used as an astronomical tool. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2009.

In this thesis, several theoretical concepts relating to the large-scale structure of the universe are presented. In particular, various aspects of the hierarchical scenario are investigated. The initial perturbation field and its early evolution are discussed in Chapter 3. Chapter 4 is concerned with two-point correlation functions for galaxies, clusters and super-clusters. In Chapter 5, some effects of using velocity as a distance measure are examined. In particular, it will be argued that caustics in redshift space are an almost inevitable feature of the hierarchical scenario. Chapter 6 concentrates on the possibity that quasar Ly-α absorption lines are redshift caustics.

Thesis (doctoral)--Rijksuniversiteit te Leiden, 1984. / Includes bibliographical references.

We study the orientations of satellite galaxies in redMaPPer clusters constructed from the Sloan Digital Sky Survey at 0.1 < z < 0.35 to determine whether there is any preferential tendency for satellites to point radially towards cluster centres. We analyse the satellite alignment (SA) signal based on three shape measurement methods (re-Gaussianization, de Vaucouleurs, and isophotal shapes), which trace galaxy light profiles at different radii. The measured SA signal depends on these shape measurement methods. We detect the strongest SA signal in isophotal shapes, followed by de Vaucouleurs shapes. While no net SA signal is detected using re-Gaussianization shapes across the entire sample, the observed SA signal reaches a statistically significant level when limiting to a subsample of higher luminosity satellites. We further investigate the impact of noise, systematics, and real physical isophotal twisting effects in the comparison between the SA signal detected via different shape measurement methods. Unlike previous studies, which only consider the dependence of SA on a few parameters, here we explore a total of 17 galaxy and cluster properties, using a statistical model averaging technique to naturally account for parameter correlations and identify significant SA predictors. We find that the measured SA signal is strongest for satellites with the following characteristics: higher luminosity, smaller distance to the cluster centre, rounder in shape, higher bulge fraction, and distributed preferentially along the major axis directions of their centrals. Finally, we provide physical explanations for the identified dependences and discuss the connection to theories of SA.

In the formation of galaxy groups and clusters, the dark matter haloes containing satellite galaxies are expected to be tidally stripped in gravitational interactions with the host. We use galaxy-galaxy weak lensing to measure the average mass of dark matter haloes of satellite galaxies as a function of projected distance to the centre of the host, since stripping is expected to be greater for satellites closer to the centre of the cluster. We further classify the satellites according to their stellar mass: Assuming that the stellar component of the galaxy is less disrupted by tidal stripping, stellar mass can be used as a proxy of the infall mass. We study the stellar-to-halo mass relation of satellites as a function of the cluster-centric distance to measure tidal stripping. We use the shear catalogues of the Dark Energy Survey (DES) science verification archive, the Canada-France-Hawaii Lensing Survey (CFHTLenS) and the CFHT Stripe 82 surveys, and we select satellites from the redMaPPer catalogue of clusters. For galaxies located in the outskirts of clusters, we find a stellar-to-halo mass relation in good agreement with the theoretical expectations from Moster et al. for central galaxies. In the centre of the cluster, we find that this relation is shifted to smaller halo mass for a given stellar mass. We interpret this finding as further evidence for tidal stripping of dark matter haloes in high-density environments.

We study the galaxy populations in 74 Sunyaev-Zeldovich effect selected clusters from the South Pole Telescope survey, which have been imaged in the science verification phase of the Dark Energy Survey. The sample extends up to z similar to 1.1 with 4 x 10(14)M(circle dot) <= M-200 <= 3 x 10(15)M(circle dot). Using the band containing the 4000 angstrom break and its redward neighbour, we study the colour-magnitude distributions of cluster galaxies to similar to m(*) + 2, finding that: (1) The intrinsic rest frame g - r colour width of the red sequence (RS) population is similar to 0.03 out to z similar to 0.85 with a preference for an increase to similar to 0.07 at z = 1, and (2) the prominence of the RS declines beyond z similar to 0.6. The spatial distribution of cluster galaxies is well described by the NFW profile out to 4R(200) with a concentration of c(g) = 3.59(-0.18)(+0.20), 5.37(-0.24)(+0.27) and 1.38(-0.19)(+0.21) for the full, the RS and the blue non-RS populations, respectively, but with similar to 40 per cent to 55 per cent cluster to cluster variation and no statistically significant redshift or mass trends. The number of galaxies within the virial region N-200 exhibits a mass trend indicating that the number of galaxies per unit total mass is lower in the most massive clusters, and shows no significant redshift trend. The RS fraction within R-200 is (68 +/- 3) per cent at z = 0.46, varies from similar to 55 per cent at z = 1 to similar to 80 per cent at z = 0.1 and exhibits intrinsic variation among

Measurement of the gas velocity distribution in galaxy clusters provides insight into the physics of mergers, through which large scale structures form in the Universe. Velocity estimates within the intracluster medium (ICM) can be obtained via the Sunyaev-Zel'dovich (SZ) effect, but its observation is challenging both in term of sensitivity requirement and control of systematic effects, including the removal of contaminants. In this paper we report resolved observations, at 150 and 260 GHz, of the SZ effect toward the triple merger MACS J0717.5 + 3745 (z = 0.55), using data obtained with the NIKA camera at the IRAM 30 m telescope. Assuming that the SZ signal is the sum of a thermal (tSZ) and a kinetic (kSZ) component and by combining the two NIKA bands, we extract for the first time a resolved map of the kSZ signal in a cluster. The kSZ signal is dominated by a dipolar structure that peaks at -5.1 and + 3.4 sigma, corresponding to two subclusters moving respectively away and toward us and coincident with the cold dense X-ray core and a hot region undergoing a major merging event. We model the gas electron density and line-of-sight velocity of MACS J0717.5 + 3745 as four subclusters. Combining NIKA data with X-ray observations from XMM-Newton and Chandra, we fit this model to constrain the gas line-of-sight velocity of each component, and we also derive, for the first time, a velocity map from kSZ data (i. e. that is model-dependent). Our results are consistent with previous constraints on the merger velocities, and thanks to the high angular resolution of our data, we are able to resolve the structure of the gas velocity. Finally, we investigate possible contamination and systematic effects with a special care given to radio and submillimeter galaxies. Among the sources that we detect with NIKA, we find one which is likely to be a high redshift lensed submillimeter galaxy.