Dissertations / Theses on the topic 'Galaxy clusters/dynamics study'

This thesis attempts to test several frameworks of non-Newtonian gravity in the context of galaxies and galaxy clusters. The theory most extensively discussed was that of Modified Newtonian Dynamics (MOND) with Galileon gravity, Emergent Gravity (EG) and Modified Gravity (MOG) mentioned to a lesser extent. Specifically, the main focus of this thesis was to determine whether MOND and MOND-like theories were compatible with galaxy cluster data, without the need to include cold dark matter. To do this, the paradigms of Extended MOND (EMOND), Generalised MOND (GMOND) and superfluid dark matter were investigated. The theories were outlined and applied to galaxy cluster data. The main findings of this were that EMOND and GMOND had some success with explaining galaxy cluster mass profiles, without requiring an additional dark matter component. The superfluid paradigm also enjoyed some success in galaxy clusters, which was expected as it behaves in a similar manner to the standard cold dark matter paradigm in cluster environments. However, the superfluid paradigm may have issues in the very centre of galaxy clusters due to the theory predicting constant density cores, whereas the cold dark matter paradigm predicts density cores which are cuspier. The EMOND paradigm was also tested against ultra-diffuse galaxy (UDGs) data as they appear in cluster environments, where EMOND becomes important. It was found that EMOND can reproduce the inferred mass of the UDGs, assuming they lie on the fundamental manifold (FM). The validity of the assumptions used to model the UDGs are discussed in the text. A two-body problem was also conducted in the Galileon gravity framework. The amount of additional gravitational force, compared to Newtonian was determined for a small galaxy at the edge of a galaxy cluster.

Dans les galaxies en interaction, de colossales forces de marée perturbent la morphologie des progéniteurs pour engendrer les longs bras d'étoiles, gaz et poussières que l'on observe parfois. En plus de leur effet destructeur, les forces de marée peuvent, dans certain cas, se placer dans une configuration protectrice appelée mode compressif. De tels modes protègent alors la matière en leur sein, en augmentant son énergie de liaison. Cette thèse se concentre sur l'étude de ce régime peu connu en quantifiant ses propriétés grâce à des outils numériques et analytiques appliqués à un spectaculaire système de galaxies en fusion, communément appelé les Antennes. Des simulations N-corps de cette paire de galaxies montrent la présence de modes compressifs dans les régions où les observations révèlent un sursaut de formation stellaire. De plus, les temps et énergies caractéristiques de ces modes correspondent à ceux de la formation de sous-structures autogravitantes telles que des amas stellaires et des naines de marée. Des comparaisons avec les taux de formation stellaire dérivés de simulations hydrodynamiques confirment la corrélation entre les positions des modes compressifs et les sites où la formation des étoiles est certainement amplifiée. Mis bout-à-bout, ces résultats suggèrent que les modes compressifs des champs de marée jouent un role important dans la formation et l'évolution des jeunes amas, au moins d'un point de vue statistique, sur une échelle de temps de l'ordre de dix millions d'années. Des résultats préliminaires de simulations d'associations stellaires soulignent l'importance de plonger les amas dans leur environnement galactique en évolution, pour tenir compte précisément de leur morphologie et évolution interne. Ces conclusions ont été étendues à de nombreuses configurations d'interaction et restent robustes aux variations des principaux paramètres caractérisant les paires de galaxies. Nous notons cependant une nette anti-corrélation entre l'importance du mode compressif et la distance entre ces galaxies. De nouvelles études incluant les aspects hydrodynamiques sont maintenant en cours et aideront à préciser le rôle exact du mode compressif dans la formation et la survie des amas d'étoiles. Les premières comparaisons avec de telles simulations suggèrent que les modes compressifs agissent en tant que catalyseurs ou amorces de la formation stellaire.

This thesis investigates the dynamics of galaxies around clusters in the quasi-linear regime, with the ultimate aim of providing cluster mass constraints which can be combined with weak lensing measurements in order to perform tests of General Relativity. Dark matter simulations are populated with galaxies using a halo occupation distribution, and used to develop and test models which describe di↵erent aspects of galaxy dynamics around clusters. A heuristic analytical model is presented describing the infall profile of galaxies onto a cluster of given mass, which is shown to fit the simulations remarkably well on quasilinear scales. The velocity dispersion of galaxies in the simulations is also examined, and a model developed which describes how this e↵ect varies as a function of position relative to the cluster centre. These models of galaxy infall and velocity dispersion are combined to provide predictions of the cluster-galaxy redshift space correlation function, or cosmic onion, which show a relatively good agreement with the simulations. The cosmic onion model is used to obtain cluster mass constraints from redshift space distortions observed in the simulations, in order to demonstrate the robustness of this method. In this work the uncertainty on cluster mass was estimated with all other halo parameters fixed, and was found to be approximately 2% at the 2 confidence level for a halo mass of ⇠ 1013 Msolarh1. However in practice the accuracy of these constraints depends on how many free parameters are considered in the halo occupation distribution, as some are degenerate with the cluster mass. The techniques developed here can be applied to observational data from the upcoming generation of spectroscopic galaxy surveys, potentially improving constraints on the dynamic mass of clusters measured from redshift space distortions.

Context: The majority (~85%) of the matter in the universe is composed of dark matter, a mysterious particle that does not interact via the electromagnetic force yet does interact with all other matter via the gravitational force. Many direct detection experiments have been devoted to finding interactions of dark matter with baryonic matter via the weak force. It is still possible that dark matter interacts with itself via a strong scale force and has a self-scattering cross-section of ~0.5 cm²g ^-1. In fact such a strong scale scattering force could resolve several outstanding astronomical mysteries: a discrepancy between the cuspy density profiles seen in ΛCDM simulations and the cored density profiles observed in low surface brightness galaxies, dwarf spheroidal galaxies, and galaxy clusters, as well as the discrepancy between the significant number of massive Milky Way dwarf spheroidal halos predicted by ΛCDM and the dearth of observed Milky Way dwarf spheroidal halos. Need: While such observations are in conflict with ΛCDM and suggest that dark matter may self-scatter, each suffers from a baryonic degeneracy, where the observations might be explained by various baryonic processes (e.g., AGN or supernove feedback, stellar winds, etc.) rather than self-interacting dark matter (SIDM). If dark matter lags behind the effectively collisionless galaxies then this is clear evidence that dark matter self-interacts. The expected galaxy-dark matter offset is typically >25 kpc (for cross-sections that would explain the other aforementioned issues with ΛCDM), this is larger than the scales of that are plagued by the baryonic degeneracies. Task: To test whether dark matter self-interacts we have carried out a comprehensive survey of the dissociative merging galaxy cluster DLSCL J0916.2+2951 (also known as the Musket Ball Cluster). This survey includes photometric and spectroscopic observations to quantify the position and velocity of the cluster galaxies, weak gravitational lensing observations to map and weigh the mass (i.e., dark matter which comprises ~85% of the mass) of the cluster, Sunyaev-Zel'dovich effect and X-ray observations to map and quantify the intracluster gas, and finally radio observations to search for associated radio relics, which had they been observed would have helped constrain the properties of the merger. Using this information in conjunction with a Monte Carlo analysis model I quantify the dynamic properties of the merger, necessary to properly interpret constraints on the SIDM cross-section. I compare the locations of the galaxies, dark matter and gas to constrain the SIDM cross-section. This dissertation presents this work. Findings: We find that the Musket Ball is a merger with total mass of 4.8^+3.2_-1.5×10 ¹⁴M_sun. However, the dynamic analysis shows that the Musket Ball is being observed 1.1^+1.3_-0.4 Gyr after first pass through and is much further progressed in its merger process than previously identified dissociative mergers (for example it is 3.4^+3.8 _-1.4 times further progressed that the Bullet Cluster). By observing that the dark matter is significantly offset from the gas we are able to place an upper limit on the dark matter cross-section of σ_SIDMm ^-1_DM < 8 cm²g^-1. However, we find an that the galaxies appear to be leading the weak lensing (WL) mass distribution by 20.5" (129 kpc at z=0.53) in southern subcluster, which might be expected to occur if dark matter self-interacts. Contrary to this finding though the WL mass centroid appears to be leading the galaxy centroid by 7.4" (47 kpc at z=0.53) in the northern subcluster. Conclusion: The southern offset alone suggests that dark matter self-interacts with ~83% confidence. However, when we account for the observation that the galaxy centroid appears to trail the WL centroid in the north the confidence falls to ~55%. While the SIDM scenario is slightly preferred over the CDM scenario it is not significantly so. Perspectives: The galaxy-dark matter offset measurement is dominated by random errors in each cluster. Thus measuring this offset in other dissociative mergers holds the promise of reducing our uncertainty and enabling us to: 1) state confidently whether dark matter self-interacts via a new dark sector force, or 2) constrain the dark matter cross-section to such a degree that SIDM cannot explain the aforementioned mysteries. To this end we have established the Merging Cluster Collaboration to observe and simulate an ensemble of dissociative merging clusters. We are currently in the process of analyzing six dissociative mergers with existing data, and carrying out multi-wavelength observations of a new sample of 15 radio relic identified dissociative mergers. (Abstract shortened by UMI.)

Thesis (Ph.D.)--Boston University PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.
Galaxy clusters play an important role in understanding the formation of structure in the Universe and can be used to constrain cosmological parameters. Thousands of clusters are known in the nearby Universe, but few are confirmed at large distances. Remote clusters provide a view of the early Universe, and are important for studying galaxy evolution. Here, I describe a technique for finding distant clusters using bent, double-lobed radio galaxies. These radio sources are active galactic nuclei (AGN) that result from outflows of material surrounding supermassive black holes in the centers of massive galaxies. These outflows are typically bent as a result of the relative motion between the host galaxy and the surrounding hot gas that fills clusters. Using the Sloan Digital Sky Survey (SDSS) and the Faint Images of the Radio Sky at Twenty-centimeters (FIRST) survey, I determine the frequency with which bent radio sources are associated with rich galaxy clusters in the nearby Universe (z < 0.5), as compared to non-bent radio sources. I find that > 60% of bent radio sources are located in rich cluster environments, compared to 10 - 20% of non-bent radio sources. Therefore, bent radio sources are efficient tracers for clusters and are useful as beacons of clusters at large distances. Bent radio sources may achieve their morphologies through large-scale cluster mergers that set the intracluster medium (ICM) in motion. Using a suite of substructure tests, I determine the significance of optical substructure in clusters containing radio sources. I find no preference for substructure in clusters with bent double-lobed sources compared to other types of radio sources, indicating that bent sources will not necessarily preferentially select clusters undergoing recent largescale mergers. Having established that bent radio sources efficiently locate clusters, I have obtained deep, follow-up observations at optical and near-infrared wavelengths to uncover associated distant cluster candidates. In addition, a large Spitzer Space Telescope survey is underway to observe all bent sources not detected in the SDSS. Follow-up observations reveal a large number of high-redshift candidates. Further study of these objects will lend insight into galaxy formation and evolution and feedback between an AGN and its environment at high-redshift for clusters with a range of masses.

Fornecemos uma amostra de 170 Aglomerados Globulares Galácticos (GCs) e analisamos as propriedades de sua distribuição espacial. Utilizando um vasto catálogo de nuvens escuras identificadas, listamos os GCs que estão atrás de uma ou mais delas e que podem estar submetidos a uma extinção mais complexa do que a considerada por mapas de extinção. Valores de incerteza em distância são obtidos da literatura recente e comparados com valores derivados de uma fórmula de propagação de erro. GCs são agrupados de acordo com características inusitadas, tais como idades relativamente jovens ou possível conexão com núcleos de galáxias anãs, de forma que o efeito desses grupos pode ser isolado na distribuição espacial geral. Adicionalmente, computamos o centróide da distribuição de GCs e estudamos como esse se relaciona com a distância ao centro da Galáxia. Considerando que uma formação galáctica via colapso monolítico é supostamente simétrica, investigamos assimetrias e como os valores de incerteza das distâncias as modificam. Velocidades espaciais e um potencial Galáctico são empregados para verificar se quaisquer assimetrias na distribuição espacial são devidas a objetos em movimento coerente, ou se são somente efeitos transientes.
We provide a sample of 170 Galactic Globular Clusters (GCs) and analyse its spatial distribution properties. Using a comprehensive dust cloud catalogue, we list the GCs that are behind one or more identified dust clouds and could be subjected to a more complex extinction curve than extinction catalogues consider. Distance uncertainty values are gathered from recent literature and compared to values derived from an error propagation formula. GCs are grouped according to unusual characteristics, such as relatively young age or possible connection to dwarf galaxy nuclei, so that their effect on the general distribution can be isolated. Additionally, we compute the centroid of the GC distribution and study how it relates to the distance to the centre of the Galaxy. Considering that galactic formation via monolithic collapse is expected to be symmetrical, we probe asymmetries and how distance uncertainty values modify them. Spatial velocities and a Galactic potential are used to verify if any asymmetries in the spatial distribution are due to co-moving objects, or if they are merely transient effects.

We present the 1.4-GHz catalog of the galaxy cluster field RCS J022434-0002.5, at a redshift of z = 0.773. A total of 194 sources were found within a ∼0.28 degree2 region to a 5sigma depth of ∼75 muJy. We show that the differential source counts for the cluster field are in good agreement with other radio surveys, and therefore do not indicate a strong excess of radio sources in the cluster compared to the field. We find 13 sources have optical counterparts with photometric redshifts within 1sigma of the cluster redshift and an additional 5 within 2sigma, and we consider these objects to be candidate cluster members. We use their radio luminosities to attempt to diagnose the presence of active galactic nuclei or star formation activity. We find that the cluster candidates are statistically more likely to be powered by active galactic nuclei, rather than star formation.

Clusters of galaxies are particularly interesting astrophysical systems, are the largest bound structures in the Universe, and contain fair sample of cosmic ingredients. Studies of cluster abundance as a function of mass and redshift were critical in establishing the standard model of cosmology. This dissertation presents results from X-ray imaging of massive distant (M > 10^14 M; 0:3 < z < 1.2) clusters, found via X-ray emission or Sunyaev-Zeldovich eff ect. This is the world's largest sample of massive galaxy clusters. We explore the radial and azimuthal profi les of the X-ray emitting gas and show that clusters are self-similar objects: their internal structure is largely independent of the cluster's mass or redshift, and the fractions of di fferent types of clusters does not change with redshift. We also present a new statistical technique for measuring a cluster's deviations from a perfect axisymmetric shape, which is especially useful in the case of low photon count observations of distant clusters.
Physics

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2005.
Includes bibliographical references (p. 49-50).
As gravitational lensing is susceptible to all gravitating matter-both baryonic and dark-it provides a potentially clean way to study the mass distribution of galaxy clusters. We are particularly interested in the substructure of dark matter in galaxy clusters as it signals constraints on various cosmological parameters as well as cluster evolution. Gravitationally lensed image simulations are needed in order to determine just how much can be learned from current mass reconstruction methods. We present here a comprehensive procedure for generating such a set of simulated images using shapelets (Massey et al. (2005)). These images use a catalog of galaxies from the Hubble Space Telescope data taken as part of the Cosmos Evolution Survey (COSMOS). The background galaxies are then lensed by a 1015M galaxy cluster set at a redshift of z = 0.4. Noise and a point spread function (PSF) can also be added to the images; we chose to emulate the set of COSMOS pointings from the Subaru Telescope. As the shapelets simulation software allows complete freedom over all background galaxy, noise, and PSF parameters, the methods presented here have the potential to be used to not only verify that existing mass reconstruction algorithms work, but also to help optimize specifications on future telescopes.
(cont.) We also present a preliminary strong lensing analysis of two noise- and PSF-free simulated images according to the algorithm presented in Diego et al. (2005). We found that while this procedure was able to accurately reproduce the surface mass density profile for radii greater than that of the outermost arcs used in the analysis, it failed in unexpected ways for the inner radii.
by Mossy S. Peeples.
S.B.

This dissertation contains investigations based on Molecular Dynamics (MD) of a variety of systems, from small atomic clusters to polymers in solution and in their condensed phases. The overall research is divided in three parts. First, I tested a new thermostat in the literature on the thermal equilibration of a small cluster of Lennard-Jones (LJ) atoms. The proposed thermostat is a Hamiltonian thermostat based on a logarithmic oscillator with the outstanding property that the mean value of its kinetic energy is constant independent of the mass and energy. I inspected several weak-coupling interaction models between the LJ cluster and the logarithmic oscillator in 3D. In all cases I show that this coupling gives rise to a kinetic motion of the cluster center of mass without transferring kinetic energy to the interatomic vibrations. This is a failure of the published thermostat because the temperature of the cluster is mainly due to vibrations in small atomic clusters This logarithmic oscillator cannot be used to thermostat any atomic or molecular system, small or large.

The second part of the dissertation is the investigation of the inherent structure of the polymer polyethylene glycol (PEG) solvated in three different solvents: water, water with 4% ethanol, and ethyl acetate. PEG with molecular weight of 2000 Da (PEG₂₀₀₀) is a polymer with many applications from industrial manufacturing to medicine that in bulk is a paste. However, its structure in very dilute solutions deserved a thorough study, important for the onset of aggregation with other polymer chains. I introduced a modification to the GROMOS 54A7 force field parameters for modeling PEG₂₀₀₀ and ethyl acetate. Both force fields are new and have now been incorporated into the database of known residues in the molecular dynamics package Gromacs. This research required numerous high performance computing MD simulations in the ARGO cluster of GMU for systems with about 100,000 solvent molecules. My findings show that PEG₂₀₀₀ in water acquires a ball-like structure without encapsulating solvent molecules. In addition, no hydrogen bonds were formed. In water with 4% ethanol, PEG₂₀₀₀ acquires also a ball-like structure but the polymer ends fluctuate folding outward and onward, although the general shape is still a compact ball-like structure.

In contrast, PEG₂₀₀₀ in ethyl acetate is quite elongated, as a very flexible spaghetti that forms kinks that unfold to give rise to folds and kinks in other positions along the polymer length. The behavior resembles an ideal polymer in a &thetas; solvent. A Principal Component Analysis (PCA) of the minima composing the inherent structure evidences the presence of two distinct groups of ball-like structures of PEG₂₀₀₀ in water and water with 4% ethanol. These groups give a definite signature to the solvated structure of PEG₂₀₀₀ in these two solvents. In contrast, PCA reveals several groups of avoided states for PEG₂₀₀₀ in ethyl acetate that disqualify the possibility of being an ideal polymer in a &thetas; solvent.

The third part of the dissertation is a work in progress, where I investigate the condensed phase of PEG₂₀₀₀ and study the interface between the condensed phase and the three different solvents under study. With a strategy of combining NPT MD simulations at different temperatures and pressures, PEG ₂₀₀₀ condensed phase displays the experimental density within a 1% discrepancy at 300 K and 1 atm. This is a very encouraging result on this ongoing project.

We present VIMOS-Very Large Telescope (VLT) spectroscopy of the Frontier Fields cluster MACS. J0416.1-2403 (z = 0.397). Taken as part of the CLASH-VLT survey, the large spectroscopic campaign provided more than 4000 reliable redshifts over similar to 600 arcmin(2), including similar to 800 cluster member galaxies. The unprecedented sample of cluster members at this redshift allows us to perform a highly detailed dynamical and structural analysis of the cluster out to similar to 2.2 r(200) (similar to 4Mpc). Our analysis of substructures reveals a complex system composed of a main massive cluster (M-200 similar to 0.9 x 10(15) M-circle dot and sigma(V r200) similar to 1000 km s(-1)) presenting two major features: (i) a bimodal velocity distribution, showing two central peaks separated by Delta V-rf similar to 1100 km s(-1) with comparable galaxy content and velocity dispersion, and (ii) a projected elongation of the main substructures along the NE-SW direction, with a prominent sub-clump similar to 600 kpc SW of the center and an isolated BCG approximately halfway between the center and the SW clump. We also detect a low-mass structure at z similar to 0.390, similar to 10' south of the cluster center, projected at similar to 3Mpc, with a relative line-of-sight velocity of Delta V-rf similar to 1700 km s(-1). The cluster mass profile that we obtain through our dynamical analysis deviates significantly from the "universal" NFW, being best fit by a Softened Isothermal Sphere model instead. The mass profile measured from the galaxy dynamics is found to be in relatively good agreement with those obtained from strong and weak lensing, as well as with that from the X-rays, despite the clearly unrelaxed nature of the cluster. Our results reveal an overall complex dynamical state of this massive cluster and support the hypothesis that the two main subclusters are being observed in a pre-collisional phase, in agreement with recent findings from radio and deep X-ray data. In this article, we also release the entire redshift catalog of 4386 sources in the field of this cluster, which includes 60 identified Chandra X-ray sources and 105 JVLA radio sources.

Globular clusters are tracers of the formation and evolution of their host galaxies. Kinematics, chemical abundances, age and position of the clusters allows tracing interactions between Milky Way and surrounding galaxies and outlines their chemical enrichment history. In this thesis we analyse mid-resolution spectra of about 800 red giant stars in 51 Galactic globular clusters. It is the first time that [Fe/H] and [Mg/Fe] derived in a consistent way are published for such a huge sample of globular clusters, almost 1/3 of the total number of catalogued clusters. Our metallicities are showed to be more precise than previous works based on mid-resolution spectroscopy. A turnover at [Fe/H] ~ -1.0 is found in the plot [Fe/H] vs. [Mg/Fe] for bulge and halo, although bulge seems to have a more metal-rich turnover, i.e, bulge has more efficient formation than the halo. Comparing the abundances with age the timescale for SNIa to start to become important is 1Gyr. [Fe/H] vs. age corroborates the different star formation efficiency of bulge and halo while [Mg/Fe] does not follow that. Halo was formed in mini halos or dwarf galaxies, and two multiple population clusters had their origin analysed to check it. M 22 seems to have been formed in the Milky Way while NGC 5824 possibly was originated in a dwarf galaxy, although our results are inconclusive for NGC 5824. The Galactic bulge seems to have been formed fast i.e., probably the oldest globular cluster is there. In fact HP 1 has a bluer horizontal branch than expected for its metallicity and we interpret that as an age effect. We determine its distance using light curves of variable stars in order to constrain future age determinations via colour-magnitude diagram. Finally, we investigate interaction between Milky Way and its neighbour galaxy SMC. We find that some star clusters are being stripped out of the SMC main body, which is consistent with tidal stripping scenario for the interaction between the galaxies, instead of ram pressure that would only affect gas.
Aglomerados globulares são traçadores da formação e evolução de suas galáxias. Cinemática, abundâncias químicas, idades e posições dos aglomerados permitem traçar interações entre Via Láctea e galáxias vizinhas e suas histórias de enriquecimento químico. Nesta tese analisamos espectros de média resolução de mais de 800 estrelas gigantes vermelhas em 51 aglomerados globulares Galácticos. É a primeira vez que [Fe/H] and [Mg/Fe] determinados de modo consistente são publicados para uma amostra desse porte, ~1/3 dos objetos catalogados. Nossas metalicidades são mais precisas que trabalhos anteriores similares. Uma quebra em [Fe/H] ~ -1.0 é encontrada no gráfico [Fe/H] vs. [Mg/Fe] para o bojo e halo, embora bojo parece ter uma quebra em [Fe/H] maior, i.e, bojo tem formaçãao mais eficiente que o halo. Comparando abundâncias com idade, a escala de tempo para SNIa ficar importante é 1Gano. [Fe/H] vs. idade corrobora diferentes eficiências de formação do bojo e halo, mas [Mg/Fe] vs. idade não mostra isso. O halo foi formado em mini halos ou galáxias anãs, e dois aglomerados com dispersão em [Fe/H] tiveram suas origens analisadas. M 22 parece ter sido formado na Via Láctea e NGC 5824 possivelmente foi originado em uma galáxia anã, embora os resultados são inconclusivos para NGC 5824. O bojo parece ter sido formado rapidamente e deve possuir o aglomerado mais velho. De fato, HP 1 tem um ramo horizontal mais azul que o esperado para sua metalicidade e vemos isso como um efeito da idade. Determinamos sua distância usando curvas de luz de RR Lyrae de maneira a restringir futuras determinações de idade via diagrama cor-magnitude. Finalmente, investigamos a interação entre Via Láctea e sua galáxia vizinha SMC. Encontramos aglomerados sendo removidos do corpo central da SMC, consistente com cenário de remoção por força de maré para a interação entre as galáxias, em vez de ``ram pressure\'\' que afeta só gás.

In the present thesis a thourough multiwavelength analysis of a number of galaxy clusters known to be experiencing a merger event is presented. The bulk of the thesis consists in the analysis of deep radio observations of six merging clusters, which host extended radio emission on the cluster scale. A composite optical and X–ray analysis is performed in order to obtain a detailed and comprehensive picture of the cluster dynamics and possibly derive hints about the properties of the ongoing merger, such as the involved mass ratio, geometry and time scale. The combination of the high quality radio, optical and X–ray data allows us to investigate the implications of the ongoing merger for the cluster radio properties, focusing on the phenomenon of cluster scale diffuse radio sources, known as radio halos and relics. A total number of six merging clusters was selected for the present study: A3562, A697, A209, A521, RXCJ 1314.4–2515 and RXCJ 2003.5–2323. All of them were known, or suspected, to possess extended radio emission on the cluster scale, in the form of a radio halo and/or a relic. High sensitivity radio observations were carried out for all clusters using the Giant Metrewave Radio Telescope (GMRT) at low frequency (i.e. ≤ 610 MHz), in order to test the presence of a diffuse radio source and/or analyse in detail the properties of the hosted extended radio emission. For three clusters, the GMRT information was combined with higher frequency data from Very Large Array (VLA) observations. A re–analysis of the optical and X–ray data available in the public archives was carried out for all sources. Propriety deep XMM–Newton and Chandra observations were used to investigate the merger dynamics in A3562. Thanks to our multiwavelength analysis, we were able to confirm the existence of a radio halo and/or a relic in all clusters, and to connect their properties and origin to the reconstructed merging scenario for most of the investigated cases. • The existence of a small size and low power radio halo in A3562 was successfully explained in the theoretical framework of the particle re–acceleration model for the origin of radio halos, which invokes the re–acceleration of pre–existing relativistic electrons in the intracluster medium by merger–driven turbulence. • A giant radio halo was found in the massive galaxy cluster A209, which has likely undergone a past major merger and is currently experiencing a new merging process in a direction roughly orthogonal to the old merger axis. A giant radio halo was also detected in A697, whose optical and X–ray properties may be suggestive of a strong merger event along the line of sight. Given the cluster mass and the kind of merger, the existence of a giant radio halo in both clusters is expected in the framework of the re–acceleration scenario. • A radio relic was detected at the outskirts of A521, a highly dynamically disturbed cluster which is accreting a number of small mass concentrations. A possible explanation for its origin requires the presence of a merger–driven shock front at the location of the source. The spectral properties of the relic may support such interpretation and require a Mach number M < ∼ 3 for the shock. • The galaxy cluster RXCJ 1314.4–2515 is exceptional and unique in hosting two peripheral relic sources, extending on the Mpc scale, and a central small size radio halo. The existence of these sources requires the presence of an ongoing energetic merger. Our combined optical and X–ray investigation suggests that a strong merging process between two or more massive subclumps may be ongoing in this cluster. Thanks to forthcoming optical and X–ray observations, we will reconstruct in detail the merger dynamics and derive its energetics, to be related to the energy necessary for the particle re–acceleration in this cluster. • Finally, RXCJ 2003.5–2323 was found to possess a giant radio halo. This source is among the largest, most powerful and most distant (z=0.317) halos imaged so far. Unlike other radio halos, it shows a very peculiar morphology with bright clumps and filaments of emission, whose origin might be related to the relatively high redshift of the hosting cluster. Although very little optical and X–ray information is available about the cluster dynamical stage, the results of our optical analysis suggest the presence of two massive substructures which may be interacting with the cluster. Forthcoming observations in the optical and X–ray bands will allow us to confirm the expected high merging activity in this cluster. Throughout the present thesis a cosmology with H0 = 70 km s−1 Mpc−1, m=0.3 and =0.7 is assumed.

En tant que structures liées les plus massives de l’univers, les amas de galaxies permettent d’étudier l’influence de l’environnement sur l’évolution des galaxies. Dans ce manuscrit, je présente AMASCFI, un algorithme de détection d’amas développé durant la thèse et utilise le catalogue d’amas obtenu à partir des décalages spectraux photométriques du relevé Canada France Hawaii Telescope Legacy Survey (CFHTLS) pour étudier le rôle des amas sur l’évolution des galaxies. Je démontre les bonnes performances d’AMASCFI sur Euclid et le CFHTLS à partir de données simulées. Je l’applique au CFHTLS pour lequel AMASCFI est pur à 90% et complet à 70% à z<0.7 et déduis une masse pour chaque amas détecté à partir de la richesse. J’étudie alors l'évolution en décalage spectral des fonctions de luminosité des galaxies (GLF) de type précoce (ETG) et de type tardif (LTG) à différentes masses d’amas. J’observe que la GLF des ETGs faibles décroît à grand décalage spectral, la séquence rouge (RS) étant déjà formée à z~0.7, mais enrichie par de faibles ETG à z<0.7. Cela peut être dû à la suppression de la formation stellaire (“quenching”) des LTG dans l’amas ou à l'accrétion de faibles ETG pré-traités dans des groupes en chute sur l’amas. Pour étudier le rôle de ce pré-traitement, je détecte les filaments de la toile cosmique avec la méthode de Laigle et al (2018) et montre qu’elle est bien valide à la précision du CFHTLS. En comparant les distances aux amas AMASCFI des ETG et des LTG dans les filaments, je conclue que les filaments doivent être le siège de “quenching”. Cela pourrait être dû à l’étranglement des galaxies dans les groupes de galaxies mais plus de preuves sont nécessaires
As the most massive bound structures in the universe, galaxy clusters are a powerful probe of the impact of environment on galaxy evolution. In this work, I present AMASCFI, a new cluster finder algorithm using photometric redshifts I developed during the PhD and use the cluster catalogue obtained on the Canada France Hawaii Telescope Legacy Survey (CFHTLS) to investigate the role played by clusters and their environment on galaxy evolution. We show the good performances of AMASCFI on Euclid and the CFHTLS using mock data. In particular AMASCFI is 90% pure and 70% complete to z<0.7 for the latter. We then apply AMASCFI to the CFHTLS T0007, and infer a mass for each detected cluster using richness as a proxy. Using our cluster catalogue, we study the redshift evolution of the galaxy luminosity functions (GLFs) of early-type (ETGs) and late-type (LTGs) galaxies at different cluster masses. We observe that the ETG GLF faint-end drops at high redshift, the red sequence (RS) being already formed at z~0.7, but enriched by faint ETGs at z<0.7. This could be due to quenching of LTGs in the cluster or accretion of faint ETGs pre-processed in infalling groups. To investigate the role of pre-processing, we use the method of Laigle et al (2018) to detect filaments from photometric redshifts and show that it allows to recover the 3D cosmic web at CFHTLS accuracy. We apply it to the CFHTLS and detect filaments around AMASCFI clusters. Studying the distances of ETGs and LTGs in these filaments to clusters, we conclude that some quenching occurs in filaments. We suggest that this might be due to strangulation in galaxy groups though we still lack conclusive evidence for such a mechanism

In this second installment of the series, we look at the internal kinematics of the multiple stellar populations of the globular cluster omega Centauri in one of the parallel Hubble Space Telescope (HST) fields, located at about 3.5 hal-flight radii from the center of the cluster. Thanks to the over 15 yr long baseline and the exquisite astrometric precision of the HST cameras, well-measured stars in our proper-motion catalog have errors as low as similar to 10 mu as yr(-1), and the catalog itself extends to near the hydrogen-burning limit of the cluster. We show that second-generation (2G) stars are significantly more radially anisotropic than first-generation (1G) stars. The latter are instead consistent with an isotropic velocity distribution. In addition, 1G stars have excess systemic rotation in the plane of the sky with respect to 2G stars. We show that the six populations below the main-sequence (MS) knee identified in our first paper are associated with the five main population groups recently isolated on the upper MS in the core of cluster. Furthermore, we find both 1G and 2G stars in the field to be far from being in energy equipartition, with eta(1G) = -0.007 +/- 0.026 for the former and eta(2G) = 0.074 +/- 0.029 for the latter, where eta is defined so that the velocity dispersion sigma(mu) scales with stellar mass as sigma(mu) proportional to m(-eta). The kinematical differences reported here can help constrain the formation mechanisms for the multiple stellar populations in omega Centauri and other globular clusters. We make our astro-photometric catalog publicly available.

In this paper, we report a new estimate of the absolute proper motion (PM) of the globular cluster NGC 5139 (omega Cen) as part of the HST large program GO-14118+ 14662. We analyzed a field 17 arcmin southwest of the center of omega Cen and computed PMs with epoch spans of similar to 15.1 years. We employed 45 background galaxies to link our relative PMs to an absolute reference-frame system. The absolute PM of the cluster in our field is (mu(alpha) cos delta, mu(delta))=(-3.341. 0.028, -6.557 +/- 0.043) mas yr(-1). Upon correction for the effects of viewing perspective and the known cluster rotation, this implies that for the cluster center of mass (mu(alpha) cos delta, mu(delta))=(-3.238. 0.028, -6.716 +/- 0.043) mas yr(-1). This measurement is direct and independent, has the highest random and systematic accuracy to date, and will provide an external verification for the upcoming Gaia Data Release 2. It also differs from most reported PMs for omega Cen in the literature by more than 5 sigma, but consistency checks compared to other recent catalogs yield excellent agreement. We computed the corresponding Galactocentric velocity, calculated the implied orbit of omega Cen in two different Galactic potentials, and compared these orbits to the orbits implied by one of the PM measurements available in the literature. We find a larger (by about 500 pc) perigalactic distance for omega Cen with our new PM measurement, suggesting a larger survival expectancy for the cluster in the Galaxy.

We analyze the resolved stellar populations of the faint stellar system, Crater, based on deep optical imaging taken with the Advanced Camera for Surveys on the Hubble Space Telescope. Crater's color-magnitude diagram (CMD) extends similar to 4 mag below the oldest main-sequence (MS) turnoff. Structurally, we find that Crater has a half-light radius of similar to 20 pc and no evidence for tidal distortions. We model. Crater's CMD as a simple stellar population (SSP) and alternatively by solving for its full star formation history. In both cases, Crater is well. described by an SSP with an age of similar to 7.5 Gyr, a metallicity of [ M / H] similar to 1.65, a total stellar mass of M-star similar to 1e4 M-circle dot, and. a luminosity of M-V similar to - 5.3, located at a distance of d similar to 145 kpc, with modest uncertainties due to differences in the underlying stellar evolution models. We argue that the sparse sampling of stars above the turnoff and subgiant branch are likely to be 1.0-1.4 M-circle dot blue stragglers and their evolved descendants, as opposed to intermediate- age MS stars. We find that. Crater is an unusually young cluster given its location in the Galaxy's outer halo. We discuss scenarios for Crater's origin, including the possibility of being stripped from the SMC or the accretion from lower- mass dwarfs such as Leo I or Carina. Despite uncertainty over its progenitor system, Crater appears to have been incorporated into the Galaxy more recently than z similar to 1 (8 Gyr ago), providing an important new constraint on the accretion history of the Galaxy.

We conducted a large spectroscopic survey of 336 red giants in the direction of the Leo II dwarf galaxy using Hectochelle on the Multiple Mirror Telescope, and we conclude that 175 of them are members based on their radial velocities and surface gravities. Of this set, 40 stars have never before been observed spectroscopically. The systemic velocity of the dwarf is 78.3 +/- 0.6 km s(-1) with a velocity dispersion of 7.4 +/- 0.4 km s(-1). We identify one star beyond the tidal radius of Leo II but find no signatures of uniform rotation, kinematic asymmetries, or streams. The stars show a strong metallicity gradient of -1.53 +/- 0.10 dex kpc(-1) and have a mean metallicity of -1.70 +/- 0.02 dex. There is also evidence of two different chemodynamic populations, but the signal is weak. A larger sample of stars would be necessary to verify this feature.

In this thesis work we carried out an accurate analysis of new observations of the galaxy cluster Abell 2626 in the radio and X-ray bands. Its radio emission is characterized by the presence of a system of peculiar radio sources, the arcs , whose properties differs from the properties of the common cluster diffuse radio sources. In the past years, several models have been proposed to explain their origin. Our work aims at investigating the origin of the arcs. We analyzed new JVLA observations of the cluster at 3.0 GHz and 5.5 GHz. During the radio analysis we detected the arcs at 3.0 GHz and possible evidences for extended emission inside them at 5.5 GHz. By combining archival maps at 1.4 GHz and the new ones at 3.0 GHz, we estimated that the arcs have a spectral index α ∼ -3. The analysis of a new CHANDRA observation of the cluster produced surprising results. We highlighted the a spatial connection between the radio arcs and a cold region inside the cluster core and, moreover, we discovered a cold front which coincides with the south-west junction of the radio arcs. It is well known that the turbulence inside the cold fronts is able to accelerate the relativistic particles, triggering radio emission in form of mini-halos. Under certain conditions, this emission results in form of collimated steep-spectrum arcs that traces the dynamics of the cold fronts. So we proposed a scenario, in which the arcs are not related to the precession of AGN jets, but instead are produced by non-thermal processes (particle acceleration and magnetic fled amplification) that are related to the formation and the evolution of the cold fronts in the core of Abell 2626. In this case the peculiar morphology of the arcs is the result of the dynamics of the cold fronts, that will be studied with future MHD simulations.

Thiolate monolayer-protected gold clusters (AuMPCs) are being used in various biological and biomedical applications due to their unique physical and chemical properties. The fact that gold-sulphur bonds are very stable enables the binding of biomolecules in the surface of gold clusters through a cysteine, an amino acid that contains a thiol group (SH). Specific AuMPCs-peptide conjugates can cross the blood-brain barrier without altering its integrity, opening the door for the treatment of pathologies related to the central nervous system, such as Alzheimer or Parkinson. Moreover, AuMPCs represent an alternative to the traditional fluorescence-based biosensors, due to their optical properties and its ability to bind specific antigens when certain AuMPCs-antibody conjugates are used. Several synthetic approaches based on the reduction of gold salts have been proposed to synthesize AuMPCs. In 1951 Turkevich and co-workers used sodium citrate for the reduction of chloroauric acid. In 2002 a novel synthetic method was proposed, named solvated metal atom dispersion method. In this method, neutral gold atoms were mixed with alkanethiols, resulting in the formation of AuMPCs, and molecular hydrogen was detected. This finding, together with the first crystallization and X-ray structure determination of Au102(SR)44 by Jadzinsky et.al., triggered a debate in the field, since the protons that were initially present in alkanethiols were not found in the AuMPC structure. One of the main goals of the present Thesis is to elucidate where the alkanethiol hydrogens go during the formation of the AuMPC. To this aim, ab initio metadynamics have been used to unravel the molecular mechanism of the formation of AuMPCs departing from neutral gold clusters and alkanethiols (Chapter III). Key to the usage of AuMPCs as biosensors is the better knowledge of their optical properties. The HOMO-LUMO gap, is a physical parameter related with optical properties. Density Functional Theory (DFT) is extensively used to obtain a theoretical value of the HOMO-LUMO gap, although it is known to severely underestimate it with respect to the experimental values. Nevertheless, recent computational studies using DFT have reported values of the HOMO-LUMO gap of AuMPCs in a very close agreement with the experimental ones. However, a simplified model of the real system was used, raising the question whether the agreement between the theoretical and the experimental values is fortuitous due to a compensation of errors. Our goal is to obtain HOMO-LUMO gap values using the whole experimental systems, i.e. peptides as the protecting ligands of the gold core and water as solvent (Chapter IV) to demonstrate that only a realistic model, and not only the use of appropriate DFT functionals, can lead to values comparable to the experimental ones. In a first step for the understanding of the reactivity of AuMPCs towards proteins, in Chapter V we modelled the binding of AuMPC towards an antibody. This process, known as ligand exchange reaction, is used to label proteins with gold clusters, as reducing agents cannot be used when certain biomolecules are present. Our results show that the neighbouring amino acids of the cysteine that should bind to the gold cluster play an essential role in the reaction. Finally, we focus on the study of the mechanism of the enzymatic reaction of a glycoprotein, a-1,3-glycosyltransferase. In recent years, our group has investigated the mechanism of one family of glycosyltransferases (GTs), providing its catalytic itinerary. In this thesis we extend this study to another family of GTs to elucidate whether or not a common molecular mechanism operates for GTs. This study represents one step towards the modelling of the more complex glycosyltransferases immobilized by gold nanoparticles, a promising technique for the development of automated glycosynthesis. The theoretical methods used along this thesis are detailed in Chapter II.
Los clústeres de oro protegidos por tiolatos (AuMPCs) se utilizan en varias aplicaciones biológicas y biomédicas debido a sus propiedades físicas y químicas. El hecho de que el enlace oro-azufre sea muy estable permite la unión de biomoléculas en la superficie de los clústeres de oro a través de una cisteína, un aminoácido que contiene un grupo tiol (SH). Sistemas específicos AuMPC-péptido pueden atravesar la barrera hematoencefálica sin alterar su integridad, pudiéndose utilizar para tratar patologías relacionadas con el sistema nervioso central, como el Alzheimer o el Parkinson. Además, los AuMPCs representan una alternativa a los biosensores tradicionales debido a sus propiedades ópticas y su especificidad ante ciertos antígenos cuando se escoge el sistema AuMPC-péptido adecuado. Métodos basados en la reducción de sales de oro han sido propuestos para sintetizar AuMPCs. En 1951 Turkevich y colaboradores usaron citrato sódico para la reducción de ácido cloroáurico. En 2002 un nuevo método sintético fue propuesto, denominado método de dispersión de átomos metálicos solvatados. En este método, átomos de oro neutros se mezclan con alcanotioles, resultando en la formación de AuMPCs e hidrógeno molecular. Este hecho, junto con la primera cristalización y determinación estructural de Au102(SR)44 llevada a cabo por Jadzinsky y colaboradores, desencadenó un gran debate en el campo, ya que los protones que inicialmente estaban presentes en los alcanotioles no se encontraron en la estructura cristalográfica. Uno de los objetivos de esta tesis es encontrar cómo los átomos de hidrógeno forman H2 durante la formación de AuMPCs. Con este fin, se utiliza metadinámica ab initio para descifrar el mecanismo molecular de la formación de AuMPCs partiendo de clústeres de oro neutros y alcanotioles (capítulo III). Clave para el uso de AuMPCs como biosensores es el conocimiento de sus propiedades ópticas. La energía HOMO-LUMO está relacionada con estas propiedades ópticas. La teoría del funcional de la densidad (DFT) ha sido muy utilizada para obtener valores teóricos de la energía HOMO-LUMO, aunque es sabido que subestima este valor con respecto al obtenido experimentalmente. Aún así, estudios computacionales recientes han seguido utilizando DFT para calcular valores de la energía HOMO-LUMO de AuMPCs, y sorprendentemente los valores obtenidos están de acuerdo con los resultados experimentales. Sin embargo, los sistemas estudiados siempre han sido modelos simplificados de los sistemas reales, originando la pregunta de si la coincidencia es fortuita debido a una compensación de errores. Nuestro objetivo es obtener valores de la energía HOMO-LUMO para sistemas utilizados experimentalmente, es decir, péptidos como ligandos y agua como disolvente (capítulo IV) para demostrar que únicamente un modelo realista y no sólo el uso de funcionales DFT adecuados puede dar resultados comparables con los experimentales. Como primer paso para entender la reactividad de AuMPCs frente a proteínas (capítulo V), se ha modelizado la unión de un AuMPC y un anticuerpo. Este proceso, conocido como reacción de intercambio de ligandos, se utiliza para marcar proteínas con clústeres de oro. Nuestros resultados muestran que los aminoácidos del entorno de la cisteína que debe unirse al clúster de oro juegan un papel esencial en la reacción. Finalmente nos centramos en el mecanismo enzimático de una glicoproteína, la a-1,3-glicosiltransferasa. Recientemente nuestro grupo ha investigado el mecanismo de una familia de glicosiltransferasas (GTs), obteniendo su itinerario catalítico. En esta tesis hemos extendido dicho estudio a otra familia de GTs para averiguar si existe un mecanismo común para todas las GTs. Este estudio representa un primer paso para la modelización de sistemas más complejos de GTs inmovilizadas por AuMPCs, una técnica prometedora para el desarrollo de glicosíntesis automatizada. Los métodos teóricos utilizados en la tesis se describen en el capítulo II.

Questo lavoro di tesi è il primo studio X-ray dedicato all’ammasso di galassie Abell 795 (z ∼ 0.137). L’analisi è stata svolta con l’obiettivo di descrivere accuratamente le proprietà dell’emissione X di A795, e di mettere in relazione le proprietà dell’ICM con le caratteristiche della BCG, una radio galassia compatta di tipo FR0, per capire se l’ambiente può impedire la formazione di una morfologia radio estesa. Abbiamo esaminato un’osservazione di archivio non ancora pubblicata del telescopio Chandra (esposizione di 29.7 ks), compiendo un’analisi dettagliata sia dell’ammasso che della sorgente centrale. Sono state misurate le proprietà complessive di A795: i risultati suggeriscono che questo sistema ha un weakly cool core, e che sono presenti perturbazioni dinamiche. In particolare, l’analisi morfologica ha rivelato un complesso ambiente centrale: abbiamo scoperto una spirale dovuta allo sloshing che si estende fino a ≈180 kpc in direzione nord-ovest dal centro dell’ammasso; lungo la spirale sono presenti due cold fronts a una distanza di ∼60 kpc e ∼178 kpc dal picco X. Abbiamo investigato l’effetto dello sloshing sul raffreddamento dell’ICM, ed è stata prodotta una stima del tempo scala che regola l’oscillazione del gas nella buca di potenziale dell’ammasso. Inoltre, la ricerca di dati radio d’archivio ci ha permesso di evidenziare la presenza di emissione radio diffusa, coincidente con la regione di sloshing: sono state descritte le proprietà di questa sorgente estesa, che abbiamo tentato di classificare come ”mini alone”. L’analisi dell’emissione X della FR0 centrale suggerisce che, almeno in questo caso, l’ambiente non è il principale responsabile della mancanza di emissione radio estesa, non possedendo una densità tale da giustificare una prematura distruzione dei getti. Infine, lo studio dell’ICM ha portato alla scoperta di due depressioni nell’emissione X, che sono state analizzate per capire se una FR0 può effettivamente scavare cavità.

In this thesis I test the modified Newtonian dynamics as an alternative to the cold dark matter hypothesis. In the Milky Way, I show that the dynamics of the dwarf galaxies are well described by the paradigm and I confirm its distant low surface brightness globular clusters provide a strong test, for which I make predictions. Through analysis of a sample of 26 X-ray bright galaxy groups and clusters I demonstrate that the three active neutrinos and their anti-particles are insufficient to reconcile modified Newtonian dynamics with the observed temperatures of the X-ray emitting gas, nor with weak-lensing measurements, in particular for the bullet cluster. To this end, I propose an 11eV sterile neutrino to serendipitously resolve the residual mass problem in X-ray bright groups and clusters, as well as matching the angular power spectrum of the Cosmic Microwave Background. With this in mind, I show that the large collision velocity of the bullet cluster and the high number of colliding clusters is more naturally reproduced in MOND than in standard dynamics.

Une étude théorique couplée à une partie expérimentale a été entreprise sur la dynamique de l'échange de ligand sur des surfaces de nanoclusters (GNC) dans le but de montrer qu'il était possible de contrôler les propriétés structurales et optiques de GNC à travers la composition de la couronne de ligand. Nos études de calcul ont été effectuées par la théorie fonctionnelle de la densité en chimie quantique (approche Kohn - Sham). Nous avons analysé les principales caractéristiques UV - Visible des spectres calculés par TD - DFT / niveau de CAMB3LYP pour les clusters métalliques Au13, Au25 et Au28 protégées par des ligands thiolate, chlorure, et phosphine. Nos résultats montrent qu'il est possible de régler l'énergie de la bande d'absorption la plus basse des clusters d'or par une répartition spécifique des ligands qui contrôle de fait la répartition des charges entre la couronne de ligand et le noyau métallique.En parallèle, nous avons synthétisé une série de clusters de composition Au25 (ATP)x (TP) 18 - x avec 4ATP (4 - aminothiophénol) et TP (thiophénol) par synthèse directe et par échange de ligands. Les mesures de spectroscopie de masse ESI - MS montrent que la nucléarité Au25 est préservée pour tous ces différents clusters. En revanche, l'échange de ligands TP par le DDT (1 - dodécanethiol) dans le mélange conduit à la formation de nanoparticules. Les mesures de spectroscopies IR confirment la présence de deux ligands différents sur la surface de l'or et les analyses SAXS montrent que nous avons une bonne corrélation entre la distance entre deux cœurs métalliques et la longueur du ligand de surface
We performed a joint computational – experimental investigation of the dynamics of ligand exchange on gold nanoclusters (GNC) surface with the aim to understand how to control the structural and optical properties of GNC through the design of their ligand shell. Our computational studies were carried out in the framework of the Kohn – Sham implementation of density functional theory in quantum chemistry. We analyzed the main features of UV – Vis spectra computed at the TD – DFT / CAMB3LYP level for the Au13, Au25, and Au28 metallic cores protected by thiolate, chloride, and phosphine ligands. Our results show that it is possible to tune the energy of the lowest absorption band of gold clusters by ligand shell engineering in order to control the charge redistribution between ligand shell and metallic core.In parallel we synthesized a set of Au25(ATP)x(TP)18 – x clusters with different ATP/TP ratios using an adapted Demessence protocol by combining 4ATP (4 – aminothiophenol) and TP (thiophenol) ligands. ESI – MS measurements evidence that for these mixed ligand shells the Au25 nuclearity is preserved. However, the addition of the DDT (1 – dodecanethiol) ligand in the mixture leads to nanoparticle formation. FT – IR spectroscopy confirms the absorption of two different ligands on the gold surface and SAXS shows that we have a good correlation between the distance between two clusters and the length of the ligand protecting them.Finally, we carried out a comparison of the mode of binding and the structural and optical properties of the fully ligated PH3 and NHC GNC with metallic cores of different nuclearities

We studied the impact of graph structure and temperature has on the sizes and lifetimes of crowds (mesoscopic clusters of consensus) that form when due to Ising Spin dynamics. Spin models have proven successful in modelling the formation of global consensus in opinion for large groups of people. We focus on the case where lots of small groups form consensuses but no global consensus forms. Our results can be interpreted in the light of consumer opinion and give an explanation for fads and brand reputation. Data was obtained by performing Monte Carlo simulations of the Ising Model on various graphs, our key control parameter was the inverse temperature β =1/kBT. In the Ising Model each vertex chooses an opinion −1 or +1 each time step based on the opinions of its neighbours. Low β ≪ 1 exhibit as vertices behaving noisily (flipping opinion often), while β → 1 tend to be quieter (flipping rarely). Interactions between neighbours creates feedback loops which determine crowd properties. The simulations we perform start with β_q = 0 for 0 ≤ t < 500, then the temperature is sharply quenched to a value βq ≥ 0 and kept constant for t ∈ (500, 15000]. We analyse the data in the time period 13000 ≤ t ≤ 15000. The simulations were performed on the 2-d rectangular lattice (RL), K-degree 1-d circular lattice (CL), Erdős-Rényi (ER), and 1-d Watts-Strogatz (WS) graphs. We conclude that crowds with multiple unique feedback loops are more robust against noisy vertices and crowd-crowd interactions. On the CL many feedback loops use the same paths which makes it easy for noisy vertices to disrupt the loops simultaneously. However 1-d structure limits crowd-crowd interactions making crowds strong against absorption by their neighbours. On the RL there are many paths between vertices, thus feedback loops can be easily rerouted around noisy vertices and crowds are robust against noise. On weakly connected ER graphs many feedback loops share the same paths and thus crowds are extremely susceptible to noisy vertices. Disorder in the 1-d lattice structure in WS graphs reduces the number of feedback loops in certain regions, this makes some crowds weak against both noisy vertices and neighbouring crowds. On the RL, CL and WS graphs we observe that size of crowds changes like an anomalous diffusion process. The anomalous diffusion exponent α was determined by plotting the root mean square change in crowd size sqrt(< ΔP² >) as a function of the crowd lifetime L. On the RL changes in crowd size were super-diffusive for 0.35 ≲ β ≲ 0.65; crowds grew very large in short periods of time, however such crowds also had short lifetimes as they were constantly replaced by new crowds. This behaviour is similar to the coming and going of fads. For 0.65 ≲ β ≲ 1 crowd sizes changed sub-diffusively, crowds grew in very small amounts to very large sizes over long time periods, this is analogous to the spread of reputation through word of mouth.

Organizational ecologists have always argued for the need to take account of the whole industry while studying how certain characteristics might affect the mortality of organizations. They argued that concepts such as legitimacy and competition were the driving forces behind organizational dynamics. Recently, researchers have started to pay more attention to a usually ignored topic: audience perceptions. Legitimacy, for example, is no longer modeled as the number of organizations in a population. It is now thought to be dependent on how audience members perceive these organizations. By bringing audience members into the picture, the topic of identity has become of central importance. This thesis seeks to study how identities affect the life chances of organizations within the context of the Lebanese newspaper industry.

Die Untersuchungen der nichtskalierbaren Eigenschaften von Clustern in dem Größenregime, in dem jedes Atom zählt, zeigten, daß hier neuartige Phänomene und Funktionalität entstehen können. Dadurch motiviert wurden in dieser Arbeit: i) strukturelle und elektronische Eigenschaften sowie die Reaktivität von Metall Clustern, ii) stationäre optische Eigenschaften und iii) zeitabhängige Eigenschaften und optimale Kontrolle von ultraschnellen Prozessen in Edelmetallcluster und in nonstoichiometrischen Natrium-Fluorid Cluster, untersucht.
The study of the nonscalable properties of clusters in the size regime in which each atom counts have shown that fully new phenomena and striking new unexpected properties of small clusters can emerge. In this work three aspects have been addressed: i) the structural and electronic properties and reactivity of metal clusters, ii) stationary optical propertis and iii) real time investigation and control of ultrafast processes in noble metal and in nonstoichiometric sodium fluoride clusters.

Esta tese tem como objetivo o estudo de aspectos dinâmicos e estatísticos da matéria escura em distribuições esféricas de massa. O fato de suas partículas constituintes interagirem gravitacionalmente mas não eletromagneticamente, e portanto sua evolução ser regida por interações de longo alcance, traz algumas complicações teóricas na descrição de suas propriedades nos termos da mecânica estatística, dificuldades compartilhadas com sistemas auto-gravitantes em geral. Para melhor compreender essas propriedades, estudamos as distribuições de matéria escura em três abordagens diferentes. Na primeira, utilizamos dados observacionais, utilizando lentes gravitacionais, em aglomerados de galáxias para comparar a performance de alguns modelos propostos para o perfil de densidade da matéria escura. Dividimos estes modelos em fenomenológicos ou teóricos. Dos primeiros, todos são capazes de descrever os dados observacionais com performance comparável. Entre os modelos teóricos estudados, o modelo chamado DARKexp descreve os dados tão bem quanto os primeiros. Numa segunda abordagem, utilizamos dados de simulações numéricas para testar uma função proposta para a distribuição de velocidades das partículas. Esta função inclui a anisotropia no campo de velocidades na chamada distribuição q-gaussiana. Comparamos a performance desta função com a da função gaussiana e concluímos que a primeira representa uma melhor descrição dos dados, mesmo levando em conta a introdução de um parâmetro extra, apesar de ainda apresentar algumas discrepâncias, especialmente nas regiões internas dos halos. Por fim, discutimos a possível relevância do conceito de indistinguibilidade na determinação dos estados de equilíbrio de sistemas auto-gravitantes em geral, propondo uma associação deste conceito com o nível de mistura do sistema. Implementamos esta associação numa análise combinatória e estudamos as conseqüências para a determinação da função distribuição e do perfil de densidades. Esta associação também levanta algumas dúvidas sobre a validade da equação de Vlasov durante o processo de relaxação violenta.
This thesis aims to study the dynamic and statistical aspects of dark matter in spherical distributions. The fact that their constituent particles interact gravitationally but not electromagnetically, and therefore its evolution is governed by long-range interactions, brings some theoretical complications in their description in terms of the statistical mechanics, difficulties shared with self-gravitating systems in general. To better understand these properties, we studied the distributions of dark matter in three different approaches. First, we used observational data, using gravitational lensing in galaxy clusters to compare the performance of some proposed models for the dark matter density profile. We divide these models in phenomenological or theoretical. All of the formers are able to describe the observational data with comparable performance. Among the theoretical models studied, the model called DARKexp describes the data as well as the formers. In a second approach, we use numerical simulation data to test a proposed function for the velocity distribution. This function includes the velocity anisotropy into the so called q-Gaussian distribution. We compared the performance of this function with the Gaussian function and concluded that the first is a better description of the data, even taking into account the introduction of an extra parameter, although still presenting some discrepancies, especially in the inner regions of the halo. Finally, we discuss the relevance of the concept of indistinguishability in determining the states of equilibrium of self-gravitating systems in general, suggesting an association of this concept with the mixing level of the system. We implement this association in a combinatorial analysis and study the consequences for the determination of the distribution function and the density profile. This association also raises some questions about the validity of the Vlasov equation during the process of violent relaxation.

Le but de cette these est l'etude des agregats metalliques de sodium par la simulation numerique. Nous avons developpe deux codes de calculs de dynamique moleculaire ab initio en fonctionnelle de densite. Le premier se fonde sur le modele semi-classique de thomas-fermi etendu. La resolution est en espace reel et utilise la methode car-parrinello. Son cout est en o(n), et nous avons mis au point un pseudopotentiel qui accelere le calcul. Au sacrifice des effets de couche, nous pouvons etudier un vaste ensemble d'agregats. Nous montrons alors qu'avec un minimum d'ajustements, les agregats de sodium suivent une energetique goutte liquide. Nous avons etudie les modes vibratoires de compression et de surface, ainsi que la repartition de la charge. Nous montrons que l'energie de surface des agregats est tres sensible a la temperature, et que leur point de fusion est plus bas que celui du solide. Nous avons extrait des barrieres de fission grace a une methode de contrainte. Le deuxieme code est base sur le modele quantique de kohn-sham. La resolution est en espace reel, et son cur est le couplage de l'algorithme du point fixe de broyden pour l'auto-coherence avec l'algorithme iteratif de lanczos-davidson pour le probleme propre. Cette methode possede un cout beaucoup plus eleve. Dans un premier temps, nous avons optimise les structures de plus basse energie des petits agregats et calcule leur energetique. L'accord avec des travaux anterieurs est excellent. Puis nous avons etudie la dynamique des agregats tres charges. Nous montrons que la fission peut etre extremement sensible aux conditions initiales. Nous avons mis en evidence pour la premiere fois, que les systemes de grande fissilite multifragmentaient avec l'emission preferentielle de monomeres sur des echelles de temps inferieures a la pico-seconde. Ces resultats ont pu etre obtenus grace au developpement d'une methode originale de maillage adaptatif dont la geometrie suit celle du systeme lors de la fragmentation.

In this dissertation we aim to perform a multi-wavelength analysis of galaxy clusters. We discuss various methods for clustering in order to determine physical parameters of galaxy clusters required for this type of study. A selection of galaxy clusters was chosen from 4 papers, (Popesso et al. 2007b, Yoon et al. 2008, Loubser et al. 2008, Brownstein & Mo at 2006) and restricted by redshift and galactic latitude to reveal a sample of 40 galaxy clusters with 0.0 < z < 0.15. Data mining using Virtual Observatory (VO) and a literature survey provided some background information about each of the galaxy clusters in our sample with respect to optical, radio and X-ray data. Using the Kayes Mixture Model (KMM) and the Gaussian Mixing Model (GMM), we determine the most likely cluster member candidates for each source in our sample. We compare the results obtained to SIMBADs method of hierarchy. We show that the GMM provides a very robust method to determine member candidates but in order to ensure that the right candidates are chosen we apply a select choice of outlier tests to our sources. We determine a method based on a combination of GMM, the QQ Plot and the Rosner test that provides a robust and consistent method for determining galaxy cluster members. Comparison between calculated physical parameters; velocity dispersion, radius, mass and temperature, and values obtained from literature show that for the majority of our galaxy clusters agree within 3 range. Inconsistencies are thought to be due to dynamically active clusters that have substructure or are undergoing mergers, making galaxy member identi cation di cult. Six correlations between di erent physical parameters in the optical and X-ray wavelength were consistent with published results. Comparing the velocity dispersion with the X-ray temperature, we found a relation of T0:43 as compared to T0:5 obtained from Bird et al. (1995). X-ray luminosity temperature and X-ray luminosity velocity dispersion relations gave the results LX T2:44 and LX 2:40 which lie within the uncertainty of results given by Rozgacheva & Kuvshinova (2010). These results all suggest that our method for determining galaxy cluster members is e cient and application to higher redshift sources can be considered. Further studies on galaxy clusters with substructure must be performed in order to improve this method. In future work, the physical parameters obtained here will be further compared to X-ray and radio properties in order to determine a link between bent radio sources and the galaxy cluster environment.
MSc (Space Physics), North-West University, Potchefstroom Campus, 2013

Clusters of galaxies represent the largest laboratories in the universe for testing the incredibly chaotic physics governing the collapse of baryons into the stars, galaxies, groups, and diffuse clouds that we see today. Within the cluster environment, there are a wide variety of physical processes that may be acting to transform galaxies.

In this thesis, we combine extensive Keck spectroscopy with wide-field HST imaging to perform a detailed case study of two intermediate redshift galaxy clusters, Cl 0024+1654 (z=0.395) and MS 0451-03 (z=0.540). Leveraging a comprehensive multiwavelength data set that spans the X-ray to infrared, and with spectral-line measurements serving as the key to revealing both the recent star-formation histories and kinematics of infalling galaxies, we aim to shed light on the environmental processes that could be acting to transform galaxies in clusters.

We adopt a strategy to make maximal use of our HST-based morphologies by splitting our sample of cluster galaxies according to morphological type, characterizing signs of recent evolution in spirals and early types separately. This approach proves to be powerful in identifying galaxies that are currently being altered by an environmental interaction: early-type galaxies that have either been newly transformed or prodded back into an active phase, and spiral galaxies where star formation is being suppressed or enhanced all stand out in our sample.

We begin by using variations in the early-type galaxy population as indicators of recent activity. Because ellipticals and S0s form such a homogeneous class in the local universe, we are sensitive to even very subtle signatures of recent and current environmental interactions. This study has yielded two key results: By constructing the Fundamental Plane (FP) of Cl 0024, we observe that elliptical and S0 galaxies exhibit a high scatter in their FP residuals, which occurs only among galaxies in the cluster core, suggesting a turbulent assembly history for Cl 0024 early types. Near the Virial radius of Cl 0024, we observe a number of compact, intermediate-mass ellipticals undergoing a burst of star formation or weak AGN activity, indicated by strong [O II] emission; their locations may mark the minimum radius at which merging is effective in each cluster.

While E+S0 galaxies do prove to be sensitive indicators of environmental interaction, it is the spiral galaxies that, of course, host the bulk of star formation within and around these clusters. We therefore probe for kinematic disturbances in spiral disks by measuring resolved rotation curves from optical emission lines, and constructing the Tully-Fisher relation for spirals across Cl 0024 and MS 0451. We find that the cluster Tully-Fisher relation exhibits significantly higher scatter than the field relation. In probing for the origin of this difference, we find that the central mass densities of star-forming spirals exhibit a sharp break near the cluster Virial radius, with spirals in the cluster outskirts exhibiting significantly lower densities. We argue that these results considered together demonstrate that cluster spirals are kinematically disturbed by their environment, likely due to galaxy-galaxy interactions (harassment).

We then discuss our most powerful method of tracking galaxy evolution across Cl 0024 and MS 0451: identifying and studying "transition galaxies"-galaxies whose stellar populations or dynamical states indicate a recent or ongoing change in morphology or star formation rate. Such galaxies are often revealed by star formation histories that seem to be at odds with the galaxy morphologies: for example, spiral galaxies with no signs of star formation, or elliptical galaxies that do show signs of star formation.

We identify and study one such class of objects, the "passive spirals" in Cl 0024. These objects exhibit no emission lines in their spectra, suggesting a lack of star formation, yet are surprisingly detected in the UV, revealing the presence of young stars. By modeling the different temporal sensitivities of UV and spectroscopic data to recent activity, we show that star formation in Cl 0024 passive spirals has decayed on timescales of less than 1 Gyr, consistent with the action of "gas starvation".

We then build on and link together our previous indications of galaxy evolution at work, aiming to piece together a more comprehensive picture of how cluster galaxies are affected by their environment at intermediate redshift. To accomplish this, we document what we believe to be the first direct evidence for the transformation of spirals into S0s: through an analysis of their stellar populations and recent star formation rates, we link the passive spiral galaxies in both clusters to their eventual end states as newly generated cluster S0 galaxies. Differences between the two clusters in both the timescales and spatial location of this conversion process allow us to evaluate the relative importance of several proposed physical mechanisms that could be responsible for the transformation. Combined with other diagnostics that are sensitive to either ICM-driven galaxy evolution or galaxy-galaxy interactions, we describe a self-consistent picture of galaxy evolution in clusters.

We find that spiral galaxies within infalling groups have already begun a slow process of conversion into S0s primarily via gentle galaxy-galaxy interactions that act to quench star formation. The fates of spirals upon reaching the core of the cluster depend heavily on the cluster ICM, with rapid conversion of all remaining spirals into S0s via ram-pressure stripping in clusters where the ICM is dense. In the presence of a less-dense ICM, the conversion continues at a slower pace, with galaxy-galaxy interactions continuing to play a role along with "starvation" by the ICM. We conclude that the buildup of the local S0 population through the transformation of spiral galaxies is a heterogeneous process that nevertheless proceeds robustly across a variety of different environments from cluster outskirts to cores.

By virtue of its proximity, the Virgo Cluster is an ideal laboratory for us to test our understanding of the formation of structure in our Universe. In this spirit, we present a dynamical study of 33 gas-poor and 34 gas-rich Virgo galaxies as part of the Spectroscopic and H-band Imaging of Virgo survey. Our final spectroscopic data set was acquired at the 3.5-m telescope at the Apache Point Observatory. Hα rotation curves for the gas-rich galaxies were modelled with a multi-parameter fit function from which various velocity measurements were inferred. Analog values were measured off of the observed rotation curves, but yielded noisier scaling relations, such as the luminosity-velocity relation (also known as the Tully-Fisher relation). Our best i-band Tully-Fisher relation has slope α=-7.2 ± 0.5 and intercept M_i(2.3)=-21.5 ± 1.1 mag, matching similar previous studies. Our study takes advantage of our own, as well as literature, data; we plan to continue expanding our compilation in order to build the largest Tully-Fisher relation for a cluster to date. Following extensive testing of the IDL routine pPXF, extended velocity dispersion profiles were extracted for our gas-poor galaxies. Considering the lack of a common standard for the measurement of a fiducial galaxy velocity dispersion in the literature, we have endeavoured to rectify this situation by determining the radius at which the measured velocity dispersion, coupled with the galaxy luminosity, yields the tightest Faber-Jackson relation. We found that radius to be 1.5 R_e, which exceeds the extent of most dispersion profiles in other works. The slope of our Faber-Jackson relation is α=-4.3 ± 0.2, which closely matches the virial value of 4. This analysis will soon be applied to a study of the Virgo Cluster Fundamental Plane. Rotation correction of our dispersion profiles will also permit the study of galaxies' velocity dispersion profile shapes in an attempt to refine our understanding of the overall manifold of galaxy structural parameters.
Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2012-12-22 19:09:06.192

Stellar bars are the most important internal drivers of the evolution of disk galaxies because they efficiently redistribute mass and angular momentum in the baryonic and dark matter components of galaxies. Mounting evidence suggests that mechanisms other than major mergers of galaxies, such as minor mergers, gas accretion, and bar-driven secular processes, play an important role in galaxy evolution since a redshift z~2. In order to characterize the evolution of barred disks, this thesis presents one of the most comprehensive studies of barred galaxies in the field at low redshifts, and also as a function of environment across galaxy clusters of different densities. This work improves significantly on earlier studies by using quantitative methods to characterize bars, analyzing high-quality data from some of the largest disk galaxy samples to date, and using results across a range of Hubble types and environments to test different theoretical models for the evolution of disk galaxies. Our main results are summarized below: (1) Studies done as a part of this thesis have quantitatively shown for the first time that the optical bar fraction in z~ 0 field galaxies is a sensitive and non-monotonic function of host galaxy properties, such as the luminosity, stellar mass, and bulge-to-disk ratio. We find that at z~0, the bar fraction increases significantly from galaxies of intermediate mass and Hubble types (Sb) toward those of lower mass and late Hubble types (Sd-Sm). The behavior from intermediate to early Hubble types is more uncertain. These results, which have been subsequently confirmed by independent studies, set constraints for theoretical models and in particular underline the importance for bar growth of angular momentum exchange between the bar, disk, bulge, and dark matter halo, as well as the possible triggering of bars by external satellites and interactions with the dark matter. Furthermore, our results at optical and near-infrared wavelengths on the fraction and sizes of bars at z~0 provide the zero-redshift anchor point for studies of bars at higher redshifts with current and future space missions (e.g., ACS, WFC3, JWST), and allow us to assess the systematic effects in such studies. (2) Although cluster environments are unique laboratories for investigating the evolution of barred disks, only sparse and disparate results have emerged from early studies. In this thesis, we study barred disks in clusters using high-quality data from the Hubble Space Telescope Advanced Camera for Surveys for the moderately-rich cluster Abell 901/902 (characterized by a galaxy number density n~1,000 gal Mpc⁻³) at z~0.165, and of the Coma cluster at z~0.02, the densest cluster (n~10,000 gal Mpc⁻³) in the nearby Universe. We find that the optical bar fraction for bright, early Hubble type disk galaxies does not show a statistically significant variation (within the error bars of ± 10 to 12%) as a function of galaxy environment within the Abell 901/902 cluster, as well as between the Abell 901/902 cluster and the field. Similarly, the optical bar fraction for bright S0 galaxies shows no statistically significant variation (within the error bars of ±10%) between the Virgo, Abell 901/902, and core of the Coma clusters, even though these environments span over an order of magnitude in galaxy number density (n~300 to 10,000 gal Mpc⁻³). We suggest that the S0 bar fraction is not greatly enhanced in denser environments, such as the core of Coma, due to the predominance of high speed encounters over slow ones, the tidal heating of S0 disks, and the low gas content of S0s in rich clusters.
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