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O objetivo deste trabalho foi determinar a massa do aglomerado de galáxias RXC J1504-0248, localizado em z = 0.215, através da análise de lentes fracas, e comparar os resultados com aqueles obtidos em trabalhos anteriores através da análise de raios-X. Imagens do aglomerado foram obtidos nas bandas r\', g\' e i\' com o detector GMOS do telescópio Gemini Sul. A partir dessas imagens, contruímos um catálogo de objetos no campo usando o software Sextractor (SE) (Bertin e Arnouts, 1996). Este software também foi utilizado para classificá-los como galáxias ou estrelas. Foram identificadas 172 galáxias neste campo, que também foram detectadas no Data Release 7 do Sloan Digital Sky Survey (SDSS). Estas galáxias foram então usadas para obter uma calibração fotométrica das imagens, comparando as magnitudes instrumentais e do SDSS nas mesmas bandas. Após a calibração fotométrica, e através da comparação com imagens do CFHTLS obtidas em cores semelhantes, as galáxias foram classificadas como membros de cluster, foreground ou background, a partir de sua posição nos diagramas cor-cor e cor-magnitude. A reconstrução da massa do aglomerado através da análise de lentes gravitacionais foi realizada em duas etapas. Na primeira, foi utilizado o software IM2SHAPE, desenvolvido por Bridle et al. (1998), que modela os objetos, adicionando até três gaussianas, cada uma definida por seis parâmetros: as coordenadas do centro do objeto, x0 e y0, a elipticidade e, o ângulo de posição , o produto dos semi-eixos maior e menor ab, e a amplitude A. Inicialmente, o programa foi executado apenas para as estrelas do campo, com o objetivo de se obter uma estimativa da distribuição da PSF. A estimativa foi então utilizado como entrada para a análise das galáxias. Na segunda etapa, para estimar a massa do aglomerado foi utilizado o programa LENSENT, desenvolvido por Marshall et al. (2002), cujos parâmetros de entrada são a elipticidade das galáxias de fundo e seus erros. Na técnica de lentes gravitacionais fracas, a dependência radial da deformação das galáxias de fundo permite determinar o perfil de massa do aglomerado. Para estimar a massa, ajustamos um perfil de uma Esfera Isotérmica Singular (SIS, na sigla em inglês), e determinamos o valor da massa dentro de um raio de 3Mpc, 1.3 ± 0.6 x 10¹ Msol. O resultado é consistente com o obtido por Bohringer et al., 2005, 1.7 x 10¹ Msol, através da análise em raios-X. Comparando o mapa de distribuição de luminosidade e da emissão de raios-X concluímos que eles são muito semelhantes à distribuição superficial de massa, resultado que indica equilíbrio. / In this work we studied the galaxy cluster RXC J1504-0248, at z=0.215, from images in the bands r\', g\' and i\' obtained with Gemini South telescope. The photometric calibration was performed by comparison with field objects identified in the Sloan Digital Sky Survey (SDSS). From the analysis of color-color and color-magnitude diagrams, galaxies in the field were then divided into cluster members, background and foreground objects. We determined the PSF using the IM2SHAPE program \\cite{Bridle98}. These results enabled us to obtain the cluster projected mass distribution through a weak lensing analysis performed with the LENSENT program \\cite{Marshall02}. We also shown that the cluster luminosity distribution and the X-ray emission are consistent with the mass map. Using a SIS model, we estimated the mass of the cluster, obtaining 1.3 x 10¹ Msun, consistent with the mass obtained in a previous X-ray analysis, 1.7 x 10¹ Msun, by \\cite{Bohringer05}.

Galaxy clusters are the most massive collapsed structures in the Universe and their properties offer a crucial insight into the formation of structure. High quality observational data is forthcoming with ongoing and upcoming surveys, but simulations are needed to provide robust theoretical predictions for comparison, as well mock data for testing observational techniques. Numerical simulations are now able to accurately model a range of astrophysical processes. This is highlighted in the BAHAMAS and MACSIS simulations, which have successfully reproduced the observed scaling relations of galaxy clusters. We use these simulations to quantify the impact baryons have on the mass distribution within galaxy clusters, as well as the bias in X-ray and weak lensing mass estimates. It is shown that baryons have only a minor affect on the spins, shape and density profiles of galaxy clusters and they have no significant impact on the bias in weak lensing mass estimates. When using spectroscopic temperatures and densities, the X-ray hydrostatic mass bias decreases as a function of mass, leading to a bias of ~40% for clusters with M_500 > 10^15 solar masses. In the penultimate chapter, we use the EAGLE and C-EAGLE simulations to construct more realistic mock cluster observations. The EAGLE simulations have been shown to successfully reproduce the properties of field galaxies and they are complemented by the C-EAGLE project, which extends this work to the cluster scale. We use these simulations to construct a cluster lightcone that accounts for the impact of uncorrelated large scale structure on cluster observables, including weak lensing mass estimates, the Sunyaev-Zel'dovich parameter and X-ray luminosity.

Les amas de galaxies sont des outils cosmologiques et astrophysiques essentiels, car ce sont les objets les plus grands et les plus massifs gravitationnellement liées dans l'Univers. L'étude de leur fonction de masse, de leur fonction de corrélation et des relations d'échelle entre leur masse et différentes observables nous permettent de tester les prévisions des modèles cosmologique et les scenarii de formation des structures. Ils sont aussi d'intéressants laboratoires pour l'étude de la formation et de l'évolution des galaxies, et de leur interactions avec le milieu qui les entourent, dans d’environnements denses. Pour y parvenir, estimer précisément leur masse revêt une importance fondamentale. J’ai étudié la précision de la richesse optique calculée par l’algorithme de détection d’amas RedGOLD (Licitra et al. 2016) en tant que mass proxy, en utilisant des mesures de lentilles gravitationnelles (weak lensing) et des observations en rayon X. J’ai mesuré les masses cumulées d’un échantillon de 1323 amas de galaxies dans le CFHTLS et NGVS à 0.2<z<0.5, dans l’intervalle de richesse 10-70. J'ai testé différents modèles prenant en compte les erreurs sur la position du centre de l'amas, les effets de lentille non faible (non-weak shear), le "two-halo term", la contribution de la galaxie centrale brillante et la dispersion intrinsèque de la relation masse-richesse. J'ai montré que la correction de la position du centre est nécessaire pour éviter un biais dans la mesure de la masse, alors que l'ajout de la galaxie centrale n'affecte pas les résultats. J'ai calculer les coefficients de la relation masse-richesse et ceux de la relation d'échelle entre masses issues du weak lensing et celle estimées à partir d'observations dans les rayons X. Mes résultats sont en accord avec les simulations et les précédents travaux publiés. / Galaxy clusters are essential cosmological and astrophysical tools, since they represent the largest and most massive gravitationally bound structures in the Universe. Through the study of their mass function, of their correlation function, and of the scaling relations between their mass and different observables, we can probe the predictions of cosmological models and structure formation scenarios. They are also interesting laboratories that allow us to study galaxy formation and evolution, and their interactions with the intra-cluster medium, in dense environments. For all of these goals, an accurate estimate of cluster masses is of fundamental importance. I studied the accuracy of the optical richness obtained by the RedGOLD cluster detection algorithm (Licitra et al. 2016) as a mass proxy, using weak lensing and X-ray mass measurements. I measured stacked weak lensing cluster masses for a sample of 1323 galaxy clusters in the CFHTLS W1 and in the NGVS at 0.2<z<0.5, in the optical richness range 10-70. I tested different weak lensing mass models that account for miscentering, non-weak shear, the two-halo term, the contribution of the Brightest Cluster Galaxy, and the intrinsic scatter in the mass-richness relation. I found that the miscentering correction is necessary to avoid a bias in the measured halo masses, while the inclusion of the BCG mass does not affect the results. I calculated the coefficients of the mass-richness relation, and of the scaling relations between the lensing mass and X-ray mass proxies. My results are consistent with simulations and previous works in the literature.

The aim of this project was to explore the shapes of dark matter halos using high resolution N-body simulations. One of the main aspects explored was how well the shape can be measured through weak lensing. To explore this, simulations were run using the GADGET-2 code \cite{SPRING05} and a method used to measure ellipticities was tested \cite{oguri1}. It was found that Large Scale Structure along the line of sight diluted the measurements and made halos appear more spherical. On the other hand, substructure close to the halo introduced a bias where intrinsically elliptical halos appeared to be slightly more spherical and intrinsically spherical halos appeared to be slightly more elliptical. The effects of projection on concentration were also explored, it was concluded that halos which are most elliptical in 3D tend to appear the most concentrated in projection. Finally, we tested the possibility of using shape or concentration measurements to help break the degeneracy in $\Omega_M$ and $\sigma_8$. We found that this may be possible with $\sim$ 3000-4000 shape measurements or $\sim$ 400-500 concentration measurements.

The aim of this project was to explore the shapes of dark matter halos using high resolution N-body simulations. One of the main aspects explored was how well the shape can be measured through weak lensing. To explore this, simulations were run using the GADGET-2 code \cite{SPRING05} and a method used to measure ellipticities was tested \cite{oguri1}. It was found that Large Scale Structure along the line of sight diluted the measurements and made halos appear more spherical. On the other hand, substructure close to the halo introduced a bias where intrinsically elliptical halos appeared to be slightly more spherical and intrinsically spherical halos appeared to be slightly more elliptical. The effects of projection on concentration were also explored, it was concluded that halos which are most elliptical in 3D tend to appear the most concentrated in projection. Finally, we tested the possibility of using shape or concentration measurements to help break the degeneracy in $\Omega_M$ and $\sigma_8$. We found that this may be possible with $\sim$ 3000-4000 shape measurements or $\sim$ 400-500 concentration measurements.

O objetivo deste trabalho foi determinar a massa do aglomerado de galáxias RXC J1504-0248, localizado em z = 0.215, através da análise de lentes fracas, e comparar os resultados com aqueles obtidos em trabalhos anteriores através da análise de raios-X. Imagens do aglomerado foram obtidos nas bandas r\', g\' e i\' com o detector GMOS do telescópio Gemini Sul. A partir dessas imagens, contruímos um catálogo de objetos no campo usando o software Sextractor (SE) (Bertin e Arnouts, 1996). Este software também foi utilizado para classificá-los como galáxias ou estrelas. Foram identificadas 172 galáxias neste campo, que também foram detectadas no Data Release 7 do Sloan Digital Sky Survey (SDSS). Estas galáxias foram então usadas para obter uma calibração fotométrica das imagens, comparando as magnitudes instrumentais e do SDSS nas mesmas bandas. Após a calibração fotométrica, e através da comparação com imagens do CFHTLS obtidas em cores semelhantes, as galáxias foram classificadas como membros de cluster, foreground ou background, a partir de sua posição nos diagramas cor-cor e cor-magnitude. A reconstrução da massa do aglomerado através da análise de lentes gravitacionais foi realizada em duas etapas. Na primeira, foi utilizado o software IM2SHAPE, desenvolvido por Bridle et al. (1998), que modela os objetos, adicionando até três gaussianas, cada uma definida por seis parâmetros: as coordenadas do centro do objeto, x0 e y0, a elipticidade e, o ângulo de posição , o produto dos semi-eixos maior e menor ab, e a amplitude A. Inicialmente, o programa foi executado apenas para as estrelas do campo, com o objetivo de se obter uma estimativa da distribuição da PSF. A estimativa foi então utilizado como entrada para a análise das galáxias. Na segunda etapa, para estimar a massa do aglomerado foi utilizado o programa LENSENT, desenvolvido por Marshall et al. (2002), cujos parâmetros de entrada são a elipticidade das galáxias de fundo e seus erros. Na técnica de lentes gravitacionais fracas, a dependência radial da deformação das galáxias de fundo permite determinar o perfil de massa do aglomerado. Para estimar a massa, ajustamos um perfil de uma Esfera Isotérmica Singular (SIS, na sigla em inglês), e determinamos o valor da massa dentro de um raio de 3Mpc, 1.3 ± 0.6 x 10¹ Msol. O resultado é consistente com o obtido por Bohringer et al., 2005, 1.7 x 10¹ Msol, através da análise em raios-X. Comparando o mapa de distribuição de luminosidade e da emissão de raios-X concluímos que eles são muito semelhantes à distribuição superficial de massa, resultado que indica equilíbrio. / In this work we studied the galaxy cluster RXC J1504-0248, at z=0.215, from images in the bands r\', g\' and i\' obtained with Gemini South telescope. The photometric calibration was performed by comparison with field objects identified in the Sloan Digital Sky Survey (SDSS). From the analysis of color-color and color-magnitude diagrams, galaxies in the field were then divided into cluster members, background and foreground objects. We determined the PSF using the IM2SHAPE program \\cite{Bridle98}. These results enabled us to obtain the cluster projected mass distribution through a weak lensing analysis performed with the LENSENT program \\cite{Marshall02}. We also shown that the cluster luminosity distribution and the X-ray emission are consistent with the mass map. Using a SIS model, we estimated the mass of the cluster, obtaining 1.3 x 10¹ Msun, consistent with the mass obtained in a previous X-ray analysis, 1.7 x 10¹ Msun, by \\cite{Bohringer05}.

No description available.

No description available.

The inflationary ΛCDM cosmology currently provides an accurate description of the Universe. It has been tested using several observational techniques over a wide redshift range, and it provides a good fit to most of them. In addition, it is a surprisingly economical model, requiring only six parameters to characterize the background cosmology and its fluctuations. In this model, the Universe is dominated by a cosmological constant Λ driving an accelerated expansion, and by cold dark matter. The strongest constraints on parameters to date come from observations of the temperature and polarization anisotropies of the cosmic microwave background measured by the Planck satellite. There are, however, indications of features in the Planck power spectra, possible differences with high redshift ground-based CMB experiments, and 'tensions' between Planck and low redshift measurements of the Hubble constant and weak gravitational lensing. In this thesis, we review possible tensions and extensions to the Planck cosmology, at both high and low redshifts. We begin with the high redshift analysis, using the Planck data to test models which introduce oscillatory features in the primordial power spectrum. We also study possible departures from slow roll inflation using the generalized slow-roll formalism, which allows for order unity deviations. Although we find models which give marginal improvements on the temperature or polarization power spectra, the combination of temperature and polarization is found to be consistent with a featureless power-law primordial spectrum. We then focus on measurements of the polarized CMB sky by the South Pole Telescope collaboration, who report tension between their measurements and the ΛCDM cosmology and with the cosmological parameters determined by Planck. We find evidence of a high χ2 in the SPTpol spectra which is unlikely to be cosmological. We report consistency between the Planck and SPTpol polarization spectra over the multipoles accessible to Planck (l ∼< 1500). We then investigate tension at low redshifts. We begin with weak gravitational lensing in which a number of surveys have suggested that the amplitude of the fluctuation spectra is lower than the Planck value. We review the small-angle approximations commonly used in galaxy weak lensing analyses and their effect on cosmological parameters. We find that these approximations are perfectly adequate for present and near future experiments. We find internal inconsistencies in the recent KiDS-450 analysis involving photometric redshifts and the KiDS covariance matrix at large scales. Finally, we investigate the difference between measurements of the present day expansion rate of the Universe. We apply a novel parameterization of the inverse distance ladder to determine the present date value of the Hubble parameter H0, which assumes General Relativity but makes no further assumptions about systematic errors or the nature of dark energy. Our analysis uses baryon acoustic oscillation data and Type Ia Supernovae to constrain the expansion history assuming a value of the sound horizon determined from the CMB. Our results are in tension with recent direct determinations of H0. We conclude that this tension, if real, cannot be solved by modifications of the ΛCDM model at late times. Instead, we would require a modification of the theory at early times which reduces the sound horizon. We conclude that at this time there is no compelling evidence that conflicts with the ΛCDM cosmology either at low or at high redshifts.