No description available.

An examination of a IIIaJ plate taken on the United Kingdom Schmidt Telescope of Survey field 405 revealed a possible supercluster of clusters of galaxies. Three rich clusters could be seen grouped within one degree, and which appeared to be of similar distance. The project described in this thesis has investigated the supercluster hypothesis by determining relative (and less precisely, absolute) distances to the three component clusters. It is described how the photographic material was painstakingly reduced to relative magnitudes and colours, and how these values were calibrated using a stellar sequence photo-electrically observed using the 1m telescope at South African Astronomical Observatory. Radial velocities were determined by a process which maximises the amount of information derived from intrinsically low-precision objective prism material. It is found that the Supercluster has, within the errors, a line-of-sight dimension of twice its projected dimension; this suggests that in fact the clusters of galaxies are in as close proximity spatially as they are apparently. The distance derived to the supercluster is 550 Mpc, giving a projected diameter of 10Mpc, with a recession velocity of 47700 kms−1 which Leads to a determination of Hubble's constant: H0 = 87 ±20kms−1 Mpc−1.

No description available.

No description available.

O uso de dióxidos de metais de transição em aplicações tecnológicas é bastante amplo, pois esses compostos possuem características importantes de semicondutores. Apesar de existir um grande número de estudos experimentais e teóricos, o entendimento das propriedades estruturais e eletrônicas desses compostos ainda não é satisfatória, principalmente quando se envolve o estudo de clusters. Clusters podem ser definidos como uma fase embrionária da matéria, pois são partículas contendo um número muito reduzido de átomos em comparação com partículas macroscópicas. Logo, suas propriedades estruturais e eletrônicas são totalmente distantes da fase cristalina do material, o que permite o desenvolvimento de novos materiais para aplicações tecnológicas. Portanto, existe um grande interesse em compreender as propriedades estruturais e eletrônicas dos clusters. Neste projeto de mestrado temos como objetivo estudar as propriedades estruturais e eletrônicas de clusters de TiO2 e CeO2 , usando para isso cálculos de primeiros princípios com base na teoria do funcional da densidade (DFT). Um dos principais problemas no estudo de clusters é a determinação da estrutura atômica, devido as dificuldades experimentais envolvidas em se trabalhar com estruturas tão pequenas. Dessa forma, um dos nossos maiores desafios foi a determinação das estruturas atômicas dos clusters desses dois tipos de dióxidos de metais de transição, uma vez que, o nosso grupo (QTnano) já conta com grande experiência, principalmente no desenvolvimento e implementação de algoritimos de otimização global. Devido as dificuldades envolvidas no estudo de partículas tão pequenas, ficamos restritos ao estudo de clusters com composição (MO2)n , com n = 1-15, ou seja, os nossos maiores clusters tem um total de 45 átomos, formando estruturas com diâmetro de inferior a 3 nm. Além da obtenção das estruturas, foi realizado o estudo das propriedades eletrônicas, energéticas e vibracionais para cada uma das composições geradas, o que propiciou a melhor compreensão sobre os efeitos eletrônicos nas estrutura atômica dos clusters. / The use of transition metal dioxides in technological applications is wide spread, because these compounds have important characteristics of semiconductors. Although there a large number of theoretical and experimental studies, the acknowledgement about the structural and electronic properties these compounds are not yet satisfactory, especially when studying clusters. Clusters can be defined as an embryonic phase of matter, because they are particles that contain a very small number of atoms in comparison with macroscopic particles. So, the structural and electronic properties are very distinct of the material crystalline phase, when allow the development of new materials in technological applications. Therefore a large interest exist in understanding the structural and electronic properties of clusters. In this master\'s degree project we have as objective to study the electronic and structural properties of TiO2 and CeO2 clusters, using first principle calculations based on the density functional theory (DFT). One of the main problems in the study of clusters is to determine the atomic structure, due the experimental difficult of work with so small particles. Thus, a great challenge was to determine the atomic structures of these two different transition metal dioxides, considering that our group (QTnano), has a large knowledge in the development and implementation of global optimization algorithms. Due the difficulty involved in studying small particles, we were restricted to the clusters of composition (MO2)n, with n = 1-15. In other words, our largest clusters have 45 atoms and a diameter smaller than 3 nm. Along with securing the structures, we realize the study of electronic, energetic and vibrational properties to each generated composition, providing an understanding of electronic effects in the atomic structure of clusters.

We describe a new Large Program in progress on the Gemini North and South telescopes: Gemini Observations of Galaxies in Rich Early Environments (GOGREEN). This is an imaging and deep spectroscopic survey of 21 galaxy systems at 1 < z < 1.5, selected to span a factor > 10 in halo mass. The scientific objectives include measuring the role of environment in the evolution of low-mass galaxies, and measuring the dynamics and stellar contents of their host haloes. The targets are selected from the SpARCS, SPT, COSMOS, and SXDS surveys, to be the evolutionary counterparts of today's clusters and groups. The new red-sensitive Hamamatsu detectors on GMOS, coupled with the nod-and-shuffle sky subtraction, allow simultaneous wavelength coverage over lambda similar to 0.6-1.05 mu m, and this enables a homogeneous and statistically complete redshift survey of galaxies of all types. The spectroscopic sample targets galaxies with AB magnitudes z' < 24.25 and [3.6] mu m < 22.5, and is therefore statistically complete for stellar masses M* greater than or similar to 10(10.3) M-circle dot, for all galaxy types and over the entire redshift range. Deep, multiwavelength imaging has been acquired over larger fields for most systems, spanning u through K, in addition to deep IRAC imaging at 3.6 mu m. The spectroscopy is similar to 50 per cent complete as of semester 17A, and we anticipate a final sample of similar to 500 new cluster members. Combined with existing spectroscopy on the brighter galaxies from GCLASS, SPT, and other sources, GOGREEN will be a large legacy cluster and field galaxy sample at this redshift that spectroscopically covers a wide range in stellar mass, halo mass, and clustercentric radius.

Analytical models and simulations predict a rapid decline in the halo density profile associated with the transition from the "infalling" regime outside the halo to the "collapsed" regime within the halo. Using data from SDSS, we explore evidence for such a feature in the density profiles of galaxy clusters using several different approaches. We first estimate the steepening of the outer galaxy density profile around clusters, finding evidence for truncation of the halo profile. Next, we measure the galaxy density profile around clusters using two sets of galaxies selected on color. We find evidence of an abrupt change in galaxy colors that coincides with the location of the steepening of the density profile. Since galaxies that have completed orbits within the cluster are more likely to be quenched of star formation and thus appear redder, this abrupt change in galaxy color can be associated with the transition from single-stream to multi-stream regimes. We also use a standard model comparison approach to measure evidence for a " splashback"-like feature, but find that this approach is very sensitive to modeling assumptions. Finally, we perform measurements using an independent cluster catalog to test for potential systematic errors associated with cluster selection. We identify several avenues for future work: improved understanding of the small-scale galaxy profile, lensing measurements, identification of proxies for the halo accretion rate, and other tests. With upcoming data from the DES, KiDS, and HSC surveys, we can expect significant improvements in the study of halo boundaries.

Clusters of galaxies provide a unique opportunity to simultaneously study cosmology through low scatter scaling relations and the complex baryonic physics that occurs in cluster cores. As such it is of key importance to quantify the effects of the various physical processes that drive cluster evolution. In this thesis a sample of 30 clusters from the Millennium Gas Simulation, of masses 10^14/h Solar Masses < M200 < 10^15/h Solar Masses, were selected and run at a higher resolution using the re-simulation technique, using a modified version of Gadget-2, an N-body SPH code. Each cluster was run multiple times with increasing levels of sub-grid physics in order to separate the different effects that govern cluster evolution. The models implemented starting with non-radiative (NR), simulations then added cooling and star formation (CSF), supernova feedback (SFB) and AGN feedback model (AGN) respectively. In order to best match observations a study of supernova and AGN feedback parameters was conducted. The sample of clusters were also used to quantify the magnitude of biases created when observing clusters, in an attempt to classify the accuracy of these measurements of clusters. Additionally, the effects of the biases were also included in the estimation of the cluster mass using hydrostatic equilibrium. The best match to the observed gas, star and baryon fractions, scaling relations and gas profiles was found when powerful supernova feedback was included, which heats gas particles to 10^7K, and an AGN model whose heating temperature scales with the final virial temperature of the cluster, so that particles in a 10^14/h Solar masses and 10^15/h Solar Masses cluster are heated to 10^8K and 10^8.5 K respectively. Outside the core, this model successfully matches all the observed profiles and scaling relations excluding the spectrascopic-like temperature. The core region is simulated with come success, with pressures matching those observed but gas that is too cool and dense, resulting in an inability to reproduce the non cool core entropy profiles. Cold dense gas is more heavily weighted in the spectrascopic-like temperature, allowing significant contributions from gas in substructures and cold dense clumps of gas that are un-ascociated with any substructures and seems to be an artificial construct of SPH. When this gas is removed using the method outlines in \cite{Roncarelli2006}, temperatures outside the core match observations, but the core region is still too dense and cool. Clearly this core region requires more complex physics, possibly through implementation of an improved SPH code or more complex sub-grid physics such as that associated with the AGN feedback. The bias profiles also exhibit a similar sensitivity to the cool dense gas clumps, having a profound effect on the observed profiles and creating significant scatter in the mass estimated using hydrostatic equilibrium. Removing this cold dense gas using the Roncarelli method results in reduced biases and hydrostatic mass estimates closer to the true values. The resulting scaling relations and profiles including the effects of biases differ from those without the biases, but not significantly. It is clear that biases can affect the observed profiles and scaling relations, but this effect is minimised by excluding the coldest densest gas. As the choice of how much gas is removed is somewhat arbitrary, it is clear that further work in this field would require better SPH implementations that do not produce the erroneous dense gas clumps and the generation of mock observations using the simulated data.

A 67" x 104" area of the metal-rich globular cluster M71 was searched for variable stars using 73 CCD frames. Using mean B and V values a colour-magnitude diagram down to V ≈ 22 is constructed. Four variables were discovered, with two more stars classed as possible candidates for variability. Phase diagrams and real time light curves are presented for all variables. One variable blue straggler (or SX Phe star) has been discovered with a period of 0.d05181. Values for the mass depend on the pulsation mode assumed for this star - (0.90 ± 0.13)M. for the first overtone mode, and (1.57 ± 0.22)M. for the fundamental mode. A second variable, of similar period (0.d06053), but with a magnitude l.m75 below the main sequence turn off was also found but it may be a field star. Two candidate eclipsing binary systems were found. The most likely period of one is 0.d37244. This value, and the shape of the light curve, suggest it may be a W UMa type variable. Its position on the CMD suggests that it too may be a field star. No period was obtainable for the other candidate binary due to a lack of phase coverage. Further data is needed to confirm and strengthen these claims. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The analysis of the publicly available Hox gene sequences from the sea lamprey Petromyzon marinus provides evidence that the Hox clusters in lampreys and other vertebrate species arose from independent duplications. In particular, our analysis supports the hypothesis that the last common ancestor of agnathans and gnathostomes had only a single Hox cluster which was subsequently duplicated independently in the two lineages.