La distribution de masse dans l'Univers telle que tracée par les amas de galaxies constitue une sonde cosmologique puissante. La caractérisation des processus associés à l'origine et à la croissance des grandes structures permet de contraindre des paramètres cosmologiques via l'étude de la distribution des amas en fonction de leur masse et de leur redshift. Cependant, il existe un désaccord statistiquement significatif observé entre les contraintes cosmologiques établies par l'étude des anisotropies primaires du fond diffus cosmologique et celles issues de l'analyse de la distribution des amas de galaxies. Cela pourrait signifier que le modèle standard de la cosmologie est incomplet. L'une des méthodes d'observation des amas de galaxie exploite l'effet Sunyaev-Zel'dovich (SZ) qui permet de contraindre la pression du gaz contenu dans ces derniers. Cette observable peut être directement liée à la masse des amas via une relation d'échelle et un profil de pression. Il est donc essentiel de caractériser précisément ces derniers afin de limiter les potentiels biais et effets systématiques affectant les analyses cosmologiques. Cette thèse présente l'ensemble des travaux réalisés dans cet objectif. Elle porte sur des thématiques allant des observations SZ effectuées avec la caméra NIKA2 installée au télescope de 30 mètres de l’IRAM jusqu'à l'estimation des paramètres cosmologiques en passant par l'analyse des données brutes de NIKA2 et des cartes SZ réalisées.Une part du travail de thèse présenté dans ce document est consacrée à l'étude et l’amélioration des différentes étapes effectuées, depuis les observations d'amas de galaxies au télescope avec la caméra NIKA2 jusqu'à la production de cartes de l'effet SZ. Les procédures développées pour estimer les performances instrumentales de NIKA2 sont détaillées et la chaîne d'analyse utilisée pour réduire les données brutes est présentée.Les travaux réalisés dans cette thèse ont également consisté à caractériser les propriétés thermodynamiques d'amas de galaxies via des analyses jointes combinant les cartes SZ NIKA2 avec des données X mesurées par le satellite XMM-Newton. Nous détaillons les méthodes employées dans le logiciel de traitement des données SZ créé pour le grand programme SZ de NIKA2, la procédure de déprojection non-paramétrique développée pour caractériser le profil de pression des amas de galaxies et les résultats de la première observation SZ avec NIKA2.Les dernières activités présentées sont dédiées aux analyses réalisées afin de quantifier l'impact du grand programme SZ de NIKA2 sur la cosmologie. Nous analysons l'effet des perturbations dynamiques du milieu intra-amas sur la caractérisation du profil de pression avec NIKA2 via l'utilisation d'amas de la simulation numérique MUSIC. Finalement, nous détaillons l'étude permettant d'estimer l'impact d'une variation du profil de pression universel sur l'estimation des paramètres cosmologiques déduite du spectre de puissance de l'effet SZ mesuré par Planck. / The mass distribution in the Universe, as traced by galaxy clusters is a powerful cosmological probe. The characterization of the processes associated with the origin and the growth of the large scale structures enables constraining cosmological parameters by studying the distribution of clusters according to their mass and redshift. However, a tension is observed between the cosmological constraints established by the study of the primary anisotropies of the cosmological background and those resulting from the analysis of the distribution of galaxy clusters. This may imply that our cosmological model is incomplete. The observation of clusters from the Sunyaev-Zel'dovich (SZ) effect allows us to constrain their gas pressure. This observable can be directly linked to the mass of galaxy clusters via a scaling relation and a pressure profile. It is thus essential to characterize the latter precisely in order to limit the potential bias and systematic effects affecting cosmological analyses. This thesis presents the work carried out to this end. It covers topics ranging from SZ observations made with the NIKA2 camera installed at the IRAM 30-metre telescope to the estimation of cosmological parameters, and including the analysis of NIKA2 raw data and the SZ maps produced.Part of the thesis work presented in this document is dedicated to the study and the improvement of the different tasks carried out, from the observations of galaxy clusters with the NIKA2 camera to the production of maps of the SZ effect. The procedures developed to estimate the NIKA2 instrumental performance are detailed and the analysis pipeline used to analyze the raw data is presented.The work carried out in this thesis also consisted in characterizing the thermodynamic properties of galaxy clusters using joint analyzes that combine the NIKA2 SZ maps with X-ray data measured by the XMM-Newton satellite. We detail the methods used in the SZ data processing software created for the NIKA2 SZ large program, the non-parametric deprojection procedure developed to characterize the pressure profile of galaxy clusters and the results of the first SZ observation with NIKA2.The last activities presented are dedicated to the analyses carried out to quantify the impact of the NIKA2 SZ large program on cosmology. We analyze the effect of dynamic disturbances of the intracluster medium on the characterization of the pressure profile with NIKA2 via the use of clusters from the MUSIC N-body simulation. Finally, we detail the study realized in order to estimate the impact of a modification of the universal pressure profile on the estimation of cosmological parameters derived from the power spectrum of the SZ effect measured by Planck.

La mesure de la distribution de matière dans l'Univers offre une sonde importante pour la cosmologie. Elle peut être tracée à différentes étapes de la formation des structures en utilisant l'analyse des anisotropies primaires et secondaires du fond diffus cosmologique (CMB). Cette thèse se focalise sur l'analyse des données du satellite Planck et celles de la caméra NIKA installée au sol au télescope de 30 mètres de l'IRAM.La première partie introduit le contexte, en se concentrant sur: 1) l'inflation, qui procure une origine naturelle aux fluctuations de matière observées dans l'Univers; 2) la réionisation, qui correspond au moment où les premières étoiles se forment; 3) les amas de galaxies, qui sont les briques de l'Univers plus récent.La seconde partie se concentre sur la réduction des données de NIKA. Le développement de la chaîne d'analyse, qui permet de passer des données brutes aux cartes astrophysiques, est présenté. Elle est dédiée aux détecteurs à inductance cinétique, nouvellement développés pour la caméra NIKA. Les outils et les simulations utilisés pour caractériser les cartes sont aussi présentés.La troisième partie est dédiée à l'observation et l'analyse des amas de galaxies par effet Sunyaev-Zel'dovich (SZ), i.e. l'interaction Compton inverse entre les photons du CMB et les électrons énergétiques dans les amas. Une fois obtenues, les cartes SZ sont combinées avec des données X afin de mesurer les propriétés thermodynamiques et de matière des amas observés. Les résultats principaux sont: la première observation de l'effet SZ avec des détecteurs à inductance cinétique, la mesure du profil de pression dans un amas à haut redshift (z=0.89), l'étude de la contamination par les sources ponctuelles dans un amas résolu, et la cartographie SZ dans un amas en collision triple.La dernière partie présente l'analyse des données de Planck en polarisation. Les effets systématiques aux grandes échelles angulaires et les outils développés pour les identifier et les corriger y sont discutés. Les données en polarisation aux grandes échelles permettent à la fois de chercher les empreintes des fluctuations quantiques générées pendant l'inflation et de mesurer la réionisation. / The measurement of the matter distribution in the Universe provides valuable tests for cosmology. It can be traced at various steps of the formation of structures using the analysis of the primary and secondary anisotropies in the Cosmic Microwave Background (CMB). This thesis focuses on the data analysis of the observations of the Planck satellite and that of the ground-based camera NIKA installed at the IRAM-30m telescope.The first part introduces the context, focussing on: 1) the inflation, which provides a natural origin for the matter fluctuations seen in the Universe; 2) the reionization, which corresponds to the moment when the first stars form; 3) clusters of galaxy, that are the building blocks of the more recent Universe.The second part focuses on the data reduction of the NIKA data. The development of the data reduction pipeline, allowing to go from raw data to maps, is presented. It is dedicated for the newly developed kinetic inductance detectors used by NIKA. Tools and simulations are also constructed to characterize the maps.The third part is dedicated to the observation and the analysis of galaxy clusters through the Sunyaev-Zel'dovich (SZ) effect, i.e. the inverse Compton interaction of CMB photons and free electrons in clusters. Once recovered, the SZ maps are combined to X-ray data to measure the matter content and thermodynamic properties of the observed clusters. The main results are: the first observation of the SZ effect with kinetic inductance detectors, the measurement of the pressure profile of a high redshift cluster ($z=0.89$), the study of point source contamination in a resolved cluster, and the SZ mapping in a triple merger.The last part is dedicated to the analysis of Planck polarization data. In particular, we discuss large angular scale systematics and the tools developed to identify and correct for them. The large scales CMB polarization data allows both to search for the imprint of the quantum fluctuations generated during inflation, and to measure the reionization.

Orientador: Patricio Anibal Letelier Sotomayor / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica "Gleb Wataghin" / Made available in DSpace on 2018-08-14T18:55:47Z (GMT). No. of bitstreams: 1 Coimbra-Araujo_CarlosHenrique_D.pdf: 1401888 bytes, checksum: ea7cff271a9dd2f1aba347507e316ac1 (MD5) Previous issue date: 2009 / Resumo: Neste trabalho é apresentada uma nova abordagem teórica e semifenomenológica acerca do que dimensões extras poderiam representar na explicação do que é a matéria escura. Aqui mostra-se que a gravitação baseada numa ação de Einstein-Hilbert para espaços-tempo com dimensão acima de quatro, produz um termo de força extra nas equações de movimento de um sistema de partículas teste, o que pode ser aplicado ao problema do campo gerado por alguma estrutura autogravitante, como clusters esféricos ou discos, por exemplo. Tal resultado é explorado no cálculo de configurações que possam mimetizar uma galáxia real. As configurações calculadas são o disco fino - a partir do método de imagens - e também a distribuição isotrópica de Miyamoto-Nagai - que reproduz o comportamento idealizado de uma galáxia espiral graças à estratificação de matéria num bojo central mais um disco galático. Para tais configurações são calculadas as curvas de rotação bem como a sua estabilidade, perfis de densidade e pressão, e mostra-se que no domínio onde as curvas são estáveis há a possibilidade de se reproduzir os resultados observacionais usualmente relacionados à incidência de um halo escuro. Nos modelos apresentados, no entanto, não há inclusão de matéria escura. O cálculo de lentes gravitacionais para clusters esféricos também é desenvolvido, indicando que as dimensões extras promovem desvios capazes de explicar as anomalias nas observações astronômicas de aglomerados de galáxias. Os resultados são amplamente discutidos e algumas comparações fenomenológicas são feitas. Dos resultados em estruturas autogravitantes, conclui-se que a presença de dimensões extras (sem matéria escura) é equivalente ao procedimento usual de se adicionar matéria escura às configurações calculadas, o que poderia levar à interpretação de que a matéria escura é apenas o produto de um desconhecimento acerca da natureza do espaço-tempo / Abstract: In the present work it is showed a new theoretical and semiphenomenological approach concerning what extra dimensions could represent to explain the nature of dark matter. Here the gravitation based on an multidimensional Einstein-Hilbert action reveals that an extra force term appears in the equations of motion for a system of test particles, that can be applied for the problem of the field produced by a self gravitating structure, as for instaure spherical clusters or disks. Such results are explored in the calculation of configurations that mimic real galaxies. The computed configurations are the thin disk - from the inverse method - and also the isotropic distribution of Miyamoto-Nagai - that reproduces the idealized behavior of a disk galaxy thanks to the stratification of matter in a central bulge plus a disk. The rotation curves, the stability, density and pressure profiles are calculated. In the domain where the curves are stable it is possible to reproduce observational results usually related to a dark halo. In present models, however, there is no inclusion of dark matter. It is also presented the calculation for gravitationallensing of spherical clusters, indicating that extra dimensions promote deviations capable to explain anomalies in the astronomical observation of many galaxy clusters. The results are widely discussed and some phenomenological comparisons are made. From results for self gravitating objects, one concludes that the presence of extra dimensions (without dark matter) is equivalent to the effect due to addition of dark matter in the calculated configurations. This could lead to the interpretation where dark matter concerns to an unfamiliarity related to the real structure of spacetime / Doutorado / Relatividade e Gravitação / Doutor em Física

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.

Multiple coherent supernova explosions (SNe) in an OB association can produce a strong shock that moves through the interstellar medium (ISM). These shocks fronts carve out hot and tenuous regions in the ISM known as superbubbles. The density contour plot at three different times (0.5 Myr (left panel), 4 Myr (middle panel), 9.5 Myr (right panel)) showing different stages of superbubble evolution for n0 = 0.5 cm−3, z0 = 300 pc, and for NOB = 104. This density contour plot is produced using ZEUS-MP 2D hydrodynamic simulation with a resolution of 512 × 512 with a logarithmic grid extending from 2 pc to 2.5 kpc. For a detailed description of this figure, see Roy et. al., 2015. The evolution of a superbubble is marked by different phases, as it moves through the ISM. Consider an OB association at the center of a disk galaxy. Initially the distance of the shock front is much smaller than the disk scale height. The superbubble shell sweeps up the ISM material, and once the amount of swept up material becomes comparable to the ejected material during SNe, the superbubble enters a self-similar phase (analogous to the Sedov-Taylor phase of individual SNe). As the superbubble shell sweeps up material, its velocity decreases, and thus the corresponding post-shock temperature drops. At a temperature of ∼ 2 × 105 K (where the cooling function peaks), the superbubble shell becomes radiative and starts losing energy via radiative cooling. This radiative phase is shown in the left panel of Figure 1. The superbubble shell starts fragmenting into clumps and channels due to Rayleigh-Taylor instabilities (RTI) (which is seeded by the thermal instability; for details see Roy et. al., 2013) when the superbubble shell crosses a few times the scale height. This is represented in the middle panel of the same figure. At a much later epoch, RTI has a strong effect on the shell fragmentation and the top of the bubble is completely blown off (the right panel). In the first chapter of the thesis (reported in Sharma et. al., 2014), we show using ZEUS-MP hydrodynamic simulations that an isolated supernova loses almost all its mechanical energy within a Myr whereas superbubbles can retain up to ∼ 40% of the input energy over the lifetime of the starcluster (∼ few tens of Myr), consistent with the analytic estimate of the second chapter. We also compare different recipes (constant luminosity driven model (LD model), kinetic energy driven model (KE model) to implement SNe feedback in numerical simulations. We determine the constraints on the injection radius (within which the SNe input energy is injected) so that the supernova explosion energy realistically couples to the interstellar medium (ISM). We show that all models produce similar results if the SNe energy is injected within a very small volume ( typically 1–2 pc for typical disk parameters). The second chapter concentrates on the conditions for galactic disks to produce superbubbles which can give rise to galactic winds after breaking out of the disk. The Kompaneets formalism provides an analytic expression for the adiabatic evolution of a superbubble. In our calculation, we include radiative cooling, and implement the supernova explosion energy in terms of constant luminosity through out the life-time of the OB stars in an exponentially stratified medium (Roy et. al., 2013). We use hydrodynamic simulations (ZEUS-MP) to determine the evolution of the superbubble shell. The main result of our calculation is a clear demarcation between the energy scales of sources causing two different astrophysical phenomenon: (i) An energy injection rate of ∼ 10−4 erg cm−2 s−1 (corresponding Mach number ∼ 2–3, produced by large OB associations) is relevant for disk galaxies with synchrotron emitting gas in the extra-planar regions. (ii) A larger energy injection scale ∼ 10−3 erg cm−2 s−1, or equivalently a surface density of star formation rate ∼ 0.1 M⊙ yr−1 kpc−2 corresponding to superbubbles with high Mach number (∼ 5–10) produces galactic-scale superwinds (requires superstar clusters to evolve coherently in space and time). The stronger energy injection case also satisfies the requirements to create and maintain a multiphase halo (matches with observations). Roy et. al., 2013 also points out that Rayleigh-Taylor instability (RTI) plays an important role in the fragmentation of superbubble shell when the shell reaches a distance approximately 2–3 times the scale-height; and before the initiation of RTI, thermal instability helps to corrugate the shell and seed the RTI. Another important finding of this chapter is the analytic estimation of the energetics of superbubble shell. The shell retains almost ∼ 30% of the thermal energy after the radiative losses at the end of the lifetime of OB associations. The third chapter considers the escape of hydrogen ionizing (Lyc) photons arising from the central OB-association that depends on the superbubble shell dynamics. The escape fraction of Lyc photons is expected to decrease at an initial stage (when the superbubble is buried in the disk) as the dense shell absorbs most of the ionizing photons, whereas the subsequently formed channels (created by RTI and thermal instabilities) in the shell creates optically thin pathways at a later time (∼ 2–3 dynamical times) which help the ionizing photons to escape. We determine an escape fraction (fesc) of Lyc photons of ∼ 10 ± 5% from typical disk galaxies (within 0 ≤ z (redshift) ≤ 2) with a weak variation with disk masses (reported in Roy et. al., 2015). This is consistent with observations of local galaxies as well as constraints from the epoch of reionization. Our work connects the fesc with the fundamental disk parameters (mid-plane density (n0), scale-height (z0)) via a relation that fescαn20z03 (with a ≈ 2.2) is a constant. In the fourth chapter, we have considered a simple model of molecule formation in the superbubble shells produced in starburst nuclei. We determine the threshold conditions on the disk parameters (gas density and scale height) for the formation of molecules in superbubble shells breaking out of disk galaxies. This threshold condition implies a gas surface density of ≥ 2000 M⊙ pc−2, which translates to a SFR of ≥ 5 M⊙ yr−1 within the nuclear region of radius ∼ 100 pc, consistent with the observed SFR of galaxies hosting molecular outflows. Consideration of molecule formation in these expanding superbubble shells predicts molecular outflows with velocities ∼ 30–40 km s−1 at distances ∼ 100–200 pc with a molecular mass ∼ 106–107 M⊙, which tally with the recent ALMA observations of NGC 253. We also consider different combinations of disk parameters and predict velocities of molecule bearing shells in the range of ∼ 30–100 km s−1 with length scales of ≥ 100 pc, in rough agreement with the observations of molecules in NGC 3628 and M82 (Roy et. al., 2016, submitted to MNRAS).

Des trous noirs supermassifs (TNs) de plusieurs millions de masses solaires occupent le centre de la plupart des galaxies proches. La découverte du TN Sagittarius A* au centre de notre galaxie, La Voie lactée, l'a confirmé. Pour autant, certaines galaxies semblent dépourvues de TNs (par exemple NGC205, M33), ou alors ne posséder un TN que de quelques milliers de masses solaires. D'autre part, des TNs dans leur forme la plus lumineuse, appelés quasars, dont la luminosité est plus importante que des centaines de fois celle d'une galaxie toute entière, ont été observés à très grand décalage spectral, lorsque l'Univers n'était alors âgé que d'un milliard d'années. Les modèles de formation des TNs doivent expliquer à la fois l'existence des TNs de faibles masses observés aujourd'hui dans les galaxies de faibles masses, mais aussi leur prodigieux homologues quasars dans l'Univers jeune. La formation des TNs pose encore de nos jours de nombreuses questions: comment se forment les TNs au début de l'histoire de l'Univers? Quelle est leur masse initiale? Quelle est la masse minimale d'une galaxie pour posséder un TN? Pour répondre à ces questions et pour étudier la formation des TNs dans le contexte de l'évolution des galaxies, nous avons utilisé des simulations hydrodynamiques cosmologiques, qui offrent l'avantage de suivre l'évolution temporelle de nombreux processus comme la formation stellaire, l'enrichissement en métaux, les mécanismes de rétroactions des TNs et des supernovae. J'ai particulièrement dirigé mes recherches sur les trois principaux modèles de formation des TNs à partir du reliquat des premières étoiles, d'amas d'étoiles, ou encore par effondrement direct. / Supermassive black holes (BHs) harboured in the center of galaxies have been confirmed with the discovery of Sagittarius A* in the center of our galaxy, the Milky Way. Recent surveys indicate that BHs of millions of solar masses are common in most local galaxies, but also that some local galaxies could be lacking BHs (e.g. NGC205, M33), or at least hosting low-mass BHs of few thousands solar masses. Conversely, massive BHs under their most luminous form are called quasars, and their luminosity can be up to hundred times the luminosity of an entire galaxy. We observe these quasars in the very early Universe, less than a billion years after the Big Bang. BH formation models therefore need to explain both the low-mass BHs that are observed in low-mass galaxies today, but also the prodigious quasars we see in the early Universe.BH formation is still puzzling today, and many questions need to be addressed: How are BHs created in the early Universe? What is their initial mass? How many BHs grow efficiently? What is the occurrence of BH formation in high redshift galaxies? What is the minimum galaxy mass to host a BH? We have used cosmological hydrodynamical simulations to capture BH formation in the context of galaxy formation and evolution. Simulations offer the advantage of following in time the evolution of galaxies, and the processes related to them, such as star formation, metal enrichment, feedback of supernovae and BHs. We have particularly focused our studies on the three main BH formation models: Pop III remnant, stellar cluster, and direct collapse models.

Le décalage vers le rouge est la principale mesure par laquelle les astronomes peuvent cartographier l’Univers dans la direction radiale. Afin de tester les hypothèses d’homogénéité et d’isotropie, il est nécessaire de mesurer avec precision le décalage vers le rouge d’un grand nombre de galaxies. De plus, différents modèles cosmologiques ne peuvent être distingués qu’au travers d’une analyse précise des structures à grandes échelles tracées par ces galaxies. Pour obtenir un grand nombre de ces mesures, il est nécessaire de mener d'importantes campagnes d’observations pour établir des relevés couvrant une large portion du ciel. Ces mesures trouvent aussi d’autres applications en astronomie comme par exemple l’analyse du cisaillement gravitationnel, la calibration des mesures photométriques, l’étude des halos de matière noire, de la morphologie des galaxies, des structures à grandes échelles et de la distribution des galaxies.Dans tous les relevés de galaxies, les mesures les plus problématiques sont pour les objets de plus faible luminosité, où le bruit instrumental devient gênant, et qui se trouvent être en général les objets les plus lointains. Pour ces objets, les mesures de décalages vers le rouge peuvent souvent devenir imprécise et, la plupart du temps, elles sont simplement exclues de l’analyse en appliquant des coupures en magnitudes ou en rapport signal à bruit. Cette procédure est une méthode brutale pour séparer les mesures probablement imprécises des mesures fiables.Dans cette thèse, nous développons un algorithme permettant la mesure du décalage vers le rouge des spectres de galaxies dans le regime de faible rapport signal à bruit. La première partie de cette thèse présente les différents concepts relatifs à l’estimation du décalage vers le rouge et au débruitrage de signaux par transformation en ondelettes et filtrage par taux de fausse détection (False Detection Rate, FDR en anglais). La seconde partie détaille comment ces concepts sont mis à contribution dans l’élaboration de l’algorithme Darth Fader (Denoised and Automatic Redshifts THresholded with a False DEtection Rate). Enfin, la dernière partie présente l’application de cet algorithme à des données synthétiques générées à partir du COSMOS Mock Catalogue, mais aussi sur des données réelles tirées du relevé WiggleZ.Nous montrons que Darth Fader fonctionne efficacement à bas rapport signal à bruit étant donné un choix approprié du taux de fausse détection et d’un critère de comptage de traits caractéristiques judicieux. Nous montrons aussi que Darth Fader permet d’éliminer le continuum des spectres à bas rapport signal à bruit, ce qui rend possible l’estimation du décalage vers le rouge par corrélation croisée. Enfin, nous montrons sur des spectres de test issues du relevé WiggleZ que notre algorithme est capable d’analyser une part importante du relevé de façon autonome avec une haute précision, sans nécessiter d'inspection visuelle (alors que les données WiggleZ ont à l’origine été entièrement soumises à l’inspection visuelle). En conclusion, Darth Fader est un algorithme prometteur pour l’analyse des grands relevés de galaxies, en particulier pour exploiter les objets à faible rapport signal à bruit qui sont habituellement simplement ignorés. / Summary: Redshift is the primary measure by which astronomers can map the Universe in the radial direction. In order to test the assumptions of homogeneity and isotropy, accurate redshifts of galaxies are needed, and for a great many of them. Additionally different cosmological models can only be distinguished by careful observations of the large scale structure traced by these galaxies. Large sky surveys are the only mechanism by which redshifts for a large number of galaxies can be obtained. Accurate redshift estimation is additionally required for many other fields of astronomy including but not limited to: weak lensing, studies of dark matter haloes, galaxy morphology studies, chemical evolution studies, photometric calibration, and studies of large scale structure and galaxy clustering.Problems exist in all surveys at the dim limit of observation, which usually corresponds to the higher redshift objects in the survey, where noise becomes problematic. Magnitude or signal-to-noise ratio cuts are often employed in order to eliminate potentially troublesome objects; such a procedure is a blunt tool for separating good redshift candidates from ones likely to be inaccurate.In this thesis we develop an algorithm to tackle redshift estimation of galaxy spectra in the low signal-to-noise regime. The first part of this thesis introduces the concepts of denoising, particularly False Detection Rate denoising, wavelet transforms and redshift estimation algorithms. The second part details how these concepts are united into the Darth Fader (Denoised and Automatic Redshifts THresholded with a FAlse DEtection Rate) algorithm. The final parts of this thesis apply the algorithm both to idealised synthetic data generated from the COSMOS Mock Catalogue, and to a subset of real data from the WiggleZ survey.We show that Darth Fader can operate effectively at low signal-to-noise given an appropriate choice of FDR parameter for denoising, and an appropriate feature-counting criterion. We also show that Darth Fader can remove the continua of spectra effectively at low signal-to-noise for the purposes of redshift estimation by cross-correlation. Additionally we show from tests on spectra from the WiggleZ survey that our algorithm has the ability to process a substantial subset of that data without the need for visual inspection (to which the entire WiggleZ spectral survey has been subjected), and to a high degree of accuracy. We conclude that the Darth Fader algorithm has potential to be used in large-sky survey pipelines, particularly where signal-to-noise is expected to be poor.

Il est bien établit théoriquement et observationnellement que les amas de galaxies ne sont pas des objets sphèriques, et qu'ils sont beaucoup mieux décrits par la géométrie triaxiale. Malgré cela, les travaux sur la forme tri-dimensionnelle des amas de galaxies sont encore trés rares. L'objet de cette thèse est de contribuer à cette problématique naissante. L'originalité de ce travail est d'aborder ce sujet théoriquement et observationnellement. J'ai mesuré la forme d'amas de galaxies simulés, proposant des prédictions sur la forme des haloes de matière noire. J'ai ensuite développé un algorithme qui se propose de combiner des données en lentilles gravitationnelles et en rayons X afin de contraindre un modèle de haloe triaxial. L'algorithme est testé sur des données simulées. Finalement, je présente l'analyse en rayons X de Abell 1703, qui, combinée avec l'analyse en lentilles gravitationnelles, permettra de déterminer la forme de Abell 1703. / It is well established both theoretically and observationally that galaxy clusters are not spherical objects and that they are much better approximated as triaxial objects. This thesis focusses on the three dimencional shape of galaxy clusters. The originality of my approach is to tackle the problem both theoretically and observationally. First, I have measured the shape of dark matter haloes in the Millenium XXL and Sbarbine simulations, providing predictions for dark matter halo shape over 5 order in magnitude in mass. Then, I have developed an algorithm aimed at fitting simultaneously lensing and X-ray data in order to constrain a triaxial mass distribution. The algorithm is tested and characterized on mock data sets. It is found to be able to recover the input parameters. Finally, I present the X-ray analysis of galaxy cluster Abell 1703, which will be combined with the existing lensing analysis in order to investigate its shape.

L’évolution des galaxies est un sujet relativement débattu en astronomie extra-galactique, étant donné que la plupart des mécanismes responsables des propriétés observées dans les galaxies (masse, taux de formation d’étoiles, contenu en métaux, moment angulaire) sont encore peu contraints et certains ne sont probablement même pas encore observés. Ma thèse porte sur une analyse de la région entourant les galaxies, connue sous le nom de Milieu Circum Galactique (MCG). Le MCG est à l’interface entreles galaxies et le Milieu Inter Galactique (MIG) et est considéré comme le lieu de prédilection pour les échanges gazeux et énergétiques entre les galaxies et le MIG, ce qui en fait la clé pour une meilleure compréhension de l’évolution des galaxies et du destin des baryons. Je présenterai dans un premier temps l’analyse d’un échantillon de systèmes à forte absorption issuent de la spectroscopie de quasars en absorption qui tracent les régions denses en hydrogène généralement associées au MCG des galaxies.Dans un deuxième temps, je présenterai ma contribution au développement d’une mission ballon embarquant un spectrographe UV, FIREBall-2, spécialement conçu pour observer l’émission faible et diffuse du MCG des galaxies à décalage vers le rouge inférieur à 1. D’un point de vue technique, je présenterai l’étude du composant optique clé de l’instrument: le réseau. D’un point de vue modélisation, je décrirai une simulation complète des observations, qui servira à la préparation du vol prévu pour l’Automne 2017notamment en ce qui concerne la sélection des cibles, la stratégie observationelle et le traitement des données. / The evolution of galaxies is a rather hot topic in extra galactic astronomy, as many of the main mechanisms underlying the observed properties of galaxies (mass, star formation rate, metal content, angular momentum) are still poorly constraints and many of them are probably undiscovered yet. My thesis focuses on an analysis of the region surrounding galaxies, known as the Circum Galactic Medium (CGM). The CGMinterfaces the galaxy with the Inter Galactic Medium (IGM) and is thought to be the most active location for gas and energy exchanges (in and out), which makes it a key ingredient towards a better understanding of galaxy evolution and the fate of all baryons. I will present in a first part, the analysis of a sample of strong absorption features based on quasar absorption spectroscopy, that probe the dense neutral hydrogen usually associated with galaxies’ CGM. In a second part, I will present my contribution to the development of a balloon-borne UV spectrograph, FIREBall-2, specifically designed to observe the faint and diffuse emissions from the CGM of galaxies at redshifts below 1. On the technical side, I will present the characterization of the key optical component ofthe instrument: the grating. On the modeling side, I will focus on an end-to-end pixel simulation of the observations to prepare for the upcoming flight, planned for Autumn 2017, in terms of target selection, observational strategy and data analysis.

L'étude de la composition chimique et de la cinématique des étoiles de la Voie Lactée est essentielle afin de comprendre comment les grandes structures de notre Galaxie se sont formées. Les étoiles de faible masse gardent en mémoire dans leur atmosphère la composition chimique du milieu interstellaire dans lequel elles sont nées, et leur cinématique est essentielle afin de caractériser les différentes populations stellaires. Dans cette thèse, nous étudions le disque galactique, composante majeure de notre Galaxie. Dans le cadre de la mission spatiale Gaia, nous avons développé une procédure automatique de mesure d'abondances chimiques, GAUGUIN, utilisée dans le cadre du Gaia-ESO Survey GES (abondances chimiques d'éléments alpha et du pic du fer pour 10000 étoiles) et du projet AMBRE (abondances de lithium pour 7300 étoiles). GAUGUIN va être intégré au pipeline d'analyse des spectres RVS de Gaia. Nous avons étudié l'évolution des dispersions des vitesses dans le disque galactique en fonction du [Mg/Fe], utilisé comme proxy de l'âge. A partir de 6800 étoiles de GES, nous avons détecté la présence d'étoiles du disque épais cinématiquement froides mais avec des valeurs élevées du rapport [Mg/Fe], donc possiblement âgées. Dans le contexte d'un milieu turbulent, nous discutons la présence de ces étoiles dans le cadre des différents modèles de formation du disque galactique. Nous avons également montré que l'abondance du lithium dans le disque montre une croissance avec la métallicité sur le domaine -1<[M/H]<+0 dex et décroît pour les métallicités super-solaires. Enfin, le disque mince et le disque épais seraient caractérisés par des évolutions chimiques différentes en abondance de lithium. / Studying both the chemical composition and kinematics of Milky Way stars is essential to understand how big structures of our Galaxy are formed. Indeed, low-mass stars retain in their photosphere the chemical composition of the interstellar medium is which they were born. Additionally, the kinematics are essential to characterize stellar populations. In this thesis, we focus on the galactic disc, a major component of the Milky Way. In the context of the Gaia mission, we have developed an automatic procedure GAUGUIN, devoted to deriving chemical abundances. We first applied our method to the Gaia-ESO Survey (GES) data to derive alpha and iron-peak chemical abundances for 10000 stars. We then derived lithium abundances for 7300 stars from the AMBRE project. GAUGUIN is well adapted to massive spectroscopic surveys, both in terms of computation time and accuracy. GAUGUIN will be soon integrated into the RVS DPAC analysis pipeline of the Gaia mission. We studied the velocity dispersions in the galactic disc as a function of the [Mg/Fe] ratio, used as an age proxy. Thanks to 6800 GES stars, we detected thick disc stars with cool kinematics and high [Mg/Fe] ratio, so presumably old. In the generally turbulent context of the primitive galactic disc, this thesis places these results in the framework of the different disc formation and evolution scenarios. We also showed that the lithium abundance in the galactic disc increases as a function of the metallicity in the domain -1<[M/H]+0 dex and decreases at super-solar metallicities. Finally, the thin and the thick discs could be characterized by different lithium abundance evolutions.