In this thesis, I present my work related to the characterization of diffuse Galactic foregrounds for observing the polarization of the Cosmic Microwave Background (CMB) radiation, and the impact of these foregrounds on the measurement of cosmological parameters. One of the most important future challenges for cosmology is the potential detection of polarization B-modes of the CMB. Inflation is a theory that explains the extremely early Universe, and solves several problems that were present in classical cosmology. It describes the anisotropies observed in the current Universe as primordial quantum fluctuations stretched by rapid exponential expansion. A key prediction of inflation is the production of a background of primordial gravitational waves, which could be detected through the associated large-scale B-mode signal in the CMB polarization. The amplitude of the B-mode signal, which depends on the energy scale of inflation, is parametrized by the tensor-to-scalar ratio r. Diffuse emission from within our Galaxy, and other extra-Galactic sources, collectively referred to as CMB foregrounds, obscure a fraction of the cosmological signal from the CMB radiation. This is a huge problem, because they have to be cleaned using data analysis methods, called component separation. A significant challenge for the potential detection of the primordial B-mode signal is that it can be extremely small, to the extent that it can be dominated even by the residual foreground contamination after component separation. In this work, we characterize these foreground residuals and assess their impact on the cosmological parameters. We create a method to simulate observations of the microwave sky, including diffuse Galactic foregrounds, CMB realizations and instrumental noise. These simulations are used to propagate errors on the characterization of foregrounds through the analysis procedures employed in the observations of the CMB, including component separation, angular power spectra calculation and cosmological parameter estimation. We estimate the bias and the σ error for the tensor-to-scalar ratio, to quantify the impact of the foreground residuals in the cosmological signal. We also propose a novel method to model these residuals when determining cosmological parameters, in order to avoid a bias on the r parameter. We performed forecasts and optimization analyses for two proposed CMB polarization experiments: the Simon Observatory, a funded ground-based telescope that will observe the polarization of the CMB from the Atacama desert in Chile, and CORE, a proposed next-generation CMB satellite experiment. All of our work shows that the issue of foreground residuals must be considered very carefully in future studies. Foreground spectral parameters must be modelled very accurately, with errors < 0.5%, if we wish to measure a value r âˆ1⁄4 10^−3. These foreground residuals can easily be mistaken as primordial cosmological signals, so our work motivates further research into developing new data analysis techniques.

The C-Band All-Sky Survey (C-BASS) is a 1 GHz bandwidth survey of the radio sky in both intensity and polarization at a frequency of 5 GHz and with a resolution of 0.8. Northern and Southern sky coverage is provided by antennas located at the Owen’s Valley Radio Observatory (OVRO) in California, and the MeerKAT support base in South Africa, respectively. The primary science goal of C-BASS is to provide a highly sensitive C-Band all sky intensity and polarization map to augment the WMAP/Planck surveys. Removal of foregound contamination will place a limit on the success of Cosmic Microwave Background (CMB) experiments that attempt to detect the B-Mode polarization of the CMB. We will provide a HEALPix map (N_side=128) with an r.m.s. noise of 0.13 mK/pixel in Stokes Q and Stokes U, and a confusion limited r.m.s. noise of 0.8 mK/pixel in Stokes I. Removal of foregrounds at the higher frequency CMB surveys will be significantly improved by this lower frequency constraint. This thesis describes the development of the C-BASS gain-stabilized receiver capable of making sensitive measurements of both galactic total intensity and polarization. The receiver features a novel digital backend to provide spectral detail across the frequency band of interest. The analog signal conditioning uses a double sideband mixer to mix the RF frequencies to a DC–1000 MHz baseband for digitization. By changing the mixer frequency and/ or duplicating the signal conditioning and digital hardware, the RF frequency coverage can be modified for other projects. I also describe the process of converting a 7.6 m telecommunications dish to a high performance radio astronomy platform. The discussion includes dish surface measurements, optical design, and the development of an inexpensive telescope servo controller. The antenna conversion process and receiver design can be used to significantly reduce capital costs of future experiments, which is especially useful for short timescale experiments. The African VLBI (Nordling, 2012) is currently following a similar route to repurpose antennas across the African continent.

Today, there are only a limited number of surveys of the sky at 1 to 20 GHz. These frequencies lie below the all-sky surveys of WMAP and Planck, but are critical in constraining the spectral slope of Galactic synchrotron emission. Knowledge of the large-scale spectral morphology of Galactic synchrotron emission is critical in the understanding of the interstellar medium and the weak signal from the polarised cosmic microwave background. Recently, ground based observations from S-PASS, C-BASS and the QUIJOTE Multifrequency Instrument (MFI) have been populating these missing frequencies. This thesis presents the first QUIJOTE MFI maps of the Northern sky in total intensity at 11, 13, 17 and 19 GHz, and the first single-dish mapping observations of Lynds dark cloud, LDN1622 at 5 and 13.7GHz. The observations from both instruments are used to probe the nature of spinning dust emission on degree and arcminute scales within the Galaxy. A full data reduction and calibration pipeline for QUIJOTE MFI time-ordered-data is described. The absolute flux density scale uncertainty of the MFI data is between 2 and 3 per cent. The pipeline characterises key properties of the MFI, such as the RFI sources, beams, bandpasses, 1/f noise and more. A key part of the pipeline was the development of an MPI ready Destriping map-maker and a maximum-likelihood map-maker. The map-making code can be applied to a range of different single-dish instruments and is used to reduce both the QUIJOTE MFI wide-survey maps of the Northern sky, and the GBT arcminute resolution raster observations of LDN 1622. A detailed discussion is given on the simulations used to test the integrity of the map-making implementation. Parametric model fitting to the SEDs of four spinning dust emission regions is performed. The MFI wide-survey maps are used in conjunction with existing multifrequency 1degree survey data. The addition of MFI maps is used to confirm the previously tentative spinning dust emission source LDN 1582/84. The mean peak frequency of spinning dust emission over the four spinning dust sources is found to be ⟨νsp⟩ = 27.2 +/- 0.7 GHz, and the mean ratio of the peak spinning dust brightness over the dust optical depth is ⟨Asp/τ250⟩ = 1.24 +/- 0.18 × 104 Jy/τ250. Spectral index maps are derived from the MFI wide-survey data in combination with 408 MHz and WMAP 23 GHz data. These maps are used to further quantify the ubiquity of spinning dust emission throughout the Galaxy. The results show that the median flux density spectral index within the inner Galactic disk for |b| < 2° is 0.24 +/- 0.07. This implies that at 23 GHz, spinning dust emission contributes 25 +/- 5 per cent of the total integrated emission within the inner disk of the Galaxy.

The C-Band All-Sky Survey (C-BASS) is a project to produce an all-sky map in intensity and polarization at a central frequency of 5 GHz with 1 GHz bandwidth and approximately 1 degree resolution. The central frequency is low enough for the map to be dominated by synchrotron and free-free emission but high enough so that Faraday rotation and depolarization are small across most of the sky. The C-BASS map will enable a more accurate removal of contaminating foregrounds from measurements of the cosmic microwave background, particularly in polarization where the B-mode signal from inflation is likely to be orders of magnitude weaker than the diffuse Galactic foreground emission. To produce an all-sky map from the ground requires two telescopes, one in the northern and one in the southern hemisphere. This thesis focuses on analysis of C-BASS North data. The noise properties of time-ordered data are characterised by fitting a noise model to periodograms. Using simulations, the errors introduced into the C-BASS maps by a destriping mapmaker are quantified and we reduce the signal error by masking the brightest pixels during baseline offset estimation. Jackknife tests are used to test the C-BASS data for systematics and to test the accuracy of the sensitivity maps. In total intensity, the spectral index of diffuse Galactic emission between 5 GHz and 408 MHz is measured using an extended T-T plot method and the results are compared to simulations. The spectral index of polarized diffuse Galactic emission between 5 GHz and 30 GHz is estimated in 55 arcminute pixels, modelling the polarized intensity as a Rician random variable.

Cette thèse présente une étude de certains effets systématiques instrumentaux et astrophysiques, pouvant affecter les performances des nouvelles et futures générations d'observations de la polarisation du fond diffus cosmologique (CMB). Nous étudions l'impact de ces effets sur les objectifs scientifiques de ces observations, ainsi que les techniques pour leur élimination. Ce travail se concentre sur les problèmes généraux que rencontrent les expériences de manière générale, mais se penche également sur les questions plus spécifiques soulevées dans le cadre de l'expérience d'observation des modes-B du CMB, POLARBEAR. L'objectif principal de l'effort actuel pour l'étude de la polarisation du CMB est une détection des anisotropies primordiales appelées modes-B --- une signature des théories inflationnaires non détectée à ce jour. Cela aurait un grand impact sur notre compréhension de l'univers, mais aussi des lois fondamentales de la physique. Comprendre, modéliser, et, finalement, éliminer ces effets systématiques sont des éléments indispensables pour tout pipeline d'analyse moderne du CMB. Sa réussite, de concert avec une haute sensibilité instrumentale, décidera du succès final des efforts entrepris. Dans cette thèse je décris tout d'abord l'optique des expériences typiques d'observation du CMB et propose un paramétrage des polarisations instrumentale et croisée. Deuxièmement, je présente un modèle décrivant la contamination atmosphérique et utilise celui-ci afin de donner quelques aperçus sur le rôle et l'impact de l'atmosphère sur les performances des expériences au sol. J'indique également comment ces résultats peuvent être utilisés pour améliorer le contrôle des effets atmosphériques dans l'analyse des données CMB. Ensuite, je discute d'une autre source d'effets systématiques venant du ciel --- les avants-plans astrophysiques polarisés. Dans ce contexte, je présente d'une part une nouvelle approche pour prédire les performances des futures expériences prenant en compte la présence des avant-plans, et d'autre part je propose un cadre pour l'optimisation des expériences afin qu'elles puissent atteindre de meilleures performances. Cette partie de la thèse est issue d'un travail commun avec F. Stivoli et R. Stompor. Je présente enfin une expèrience phare pour l'observation de la polarisation du CMB, POLARBEAR, dans laquelle j'ai été impliqué au cours de mes études doctorales. Je décris le statut actuel et les performances de l'instrument ainsi que quelques étapes de son pipeline d'analyse des données. En particulier, je montre des méthodes d'estimation de certains des paramètres introduits pour la modélisation d'effets systématiques, à partir de données simulées. Ce travail a été réalisé en collaboration avec les membres de l'équipe POLARBEAR.

This PhD thesis, written in english, studies the non-Gaussianity (NG) of extragalactic foregrounds to the Cosmic Microwave Background (CMB), the latter being one of the golden observables of today's cosmology. In the last decade has emerged research for deviations of the CMB to the Gaussian law, as they would discriminate the models for the generation of primordial perturbations. However the CMB measurements, e.g. by the Planck satellite, are contaminated by several foregrounds. I studied in particular the extragalactic foregrounds which trace the large scale structure of the universe : radio and infrared point-sources and the thermal Sunyaev-Zel'dovich effect (tSZ). I hence describe the statistical tools to characterise a random field : the correlation functions, and their harmonic counterpart : the polyspectra. In particular the bispectrum is the lowest order indicator of NG, with the highest potential signal to noise ratio (SNR). I describe how it can be estimated on data, accounting for a potential mask (e.g. galactic), and propose a method to visualise the bispectrum, which is more adapted than the already existing ones. I then describe the covariance of a polyspectrum measurement, a method to generate non-Gaussian simulations, and how the statistic of a 3D field projects onto the sphere when integrating along the line-of-sight. I then describe the generation of density perturbations by the standard inflation model and their possible NG, how they yield the CMB anisotropies and grow to form the large scale structure of today's universe. To describe this large scale structure, I present the halo model and propose a diagrammatic method to compute the polyspectra of the galaxy density field and to have a simple and powerful representation of the involved terms. I then describe the foregrounds to the CMB, galactic as well as extragalactic. I briefly describe the physics of the thermal Sunyaev-Zel'dovich effect and how to describe its spatial distribution with the halo model. I then describe the extragalactic point-sources and present a prescription for the NG of clustered sources. For the Cosmic Infrared Background (CIB) I introduce a physical modeling with the halo model and the diagrammatic method. I compute numerically the 3D galaxy bispectrum and produce the first theoretical prediction of the CIB angular bispectrum. I show the contributions of the different terms and the temporal evolution of the galaxy bispectrum. For the CIB angular bispectrum, I show its different terms, its scale and configuration dependence, and how it varies with model parameters. By Fisher analysis, I show it allows very good constraints on these parameters, complementary to or better than those coming from the power spectrum. Finally, I describe my work on measuring NG. I first introduce an estimator for the amplitude of the CIB bispectrum, and show how to combine it with similar ones for radio sources and the CMB, for a joint constraint of the different sources of NG. I quantify the contamination of extragalactic point-sources to the estimation of primordial NG ; for Planck it is negligible for the central CMB frequencies. I then describe my measurement of the CIB bispectrum on Planck data ; it is very significantly detected at 217, 353 and 545 GHz with SNR ranging from 5.8 to 28.7. Its shape is consistent between frequencies, as well as the intrinsic amplitude of NG. Ultimately, I describe my measurement of the tSZ bispectrum, on simulations and on Compton parameter maps estimated by Planck, validating the robustness of the estimation thanks to realist foreground simulations. The tSZ bispectrum is very significantly detected with SNR~200. Its amplitude and its scale and configuration dependence are consistent with the projected map of detected clusters and tSZ simulations. Finally, this measurement allows to put a constraint on the cosmological parameters : sigma_8*(Omega_b/0.049)^0.35 = 0.74+/-0.04 in agreement with other tSZ statistics.

Cette thèse, écrite en anglais, étudie la non-Gaussianité (NG) des avant-plans extragalactiques au fond de rayonnement fossile (FDC), celui-ci étant une des observables de choix de la cosmologie actuelle. Ces dernières années a émergé la recherche de déviations du FDC à la loi Gaussienne, car elles permettraient de discriminer les modèles de génération des perturbations primordiales. Cependant les mesures du FDC, e.g. par le satellite Planck, sont contaminées par différents avant-plans. J'ai étudié en particulier les avant-plans extragalactiques traçant la structure à grande échelle de l'univers: les sources ponctuelles radio et infrarouges et l'effet Sunyaev-Zel'dovich thermique (tSZ). Je décris donc les outils statistiques caractérisant un champ aléatoire : les fonctions de corrélations, et leur analogue harmonique : les polyspectres. En particulier le bispectre est l'indicateur de plus bas ordre de NG avec le plus fort rapport signal sur bruit (SNR) potentiel. Je décris comment il peut être estimé sur des données en tenant compte d'un masque (e.g. galactique), et propose une méthode de visualisation du bispectre plus adaptée que les préexistantes. Je décris ensuite la covariance d'une mesure de polyspectre, une méthode pour générer des simulations non-Gaussiennes, et comment la statistique d'un champ 3D se projette sur la sphère lors de l'intégration sur la ligne de visée. Je décris ensuite la genèse des perturbations de densité par l'inflation standard et leur possible NG, comment elles génèrent les anisotropies du FDC et croissent pour former la structure à grande échelle de l'univers actuel. Pour décrire cette dite structure, j'expose le modèle de halo et propose une méthode diagrammatique pour calculer les polyspectres du champ de densité des galaxies et avoir une représentation simple et puissante des termes impliqués. Puis je décris les avant-plans au FDC, tant galactiques que extragalactiques. J'expose la physique de l'effet tSZ et comment décrire sa distribution spatiale avec le modèle de halo. Puis je décris les sources extragalactiques et présente une prescription pour la NG de sources corrélées. Pour le fond diffus infrarouge (FDI) j'introduis une modélisation physique par le modèle de halo et la méthode diagrammatique. Je calcule numériquement le bispectre 3D des galaxies et obtiens la première prédiction du bispectre angulaire FDI. Je montre les différentes contributions et l'évolution temporelle du bispectre des galaxies. Pour le bispectre du FDI, je montre ses différents termes, sa dépendence en échelle et en configuration, et comment il varie avec les paramètres du modèle. Par analyse de Fisher, je montre qu'il apporte de fortes contraintes sur ces paramètres, complémentaires ou supérieures à celles venant du spectre. Enfin, je décris mon travail de mesure de la NG. J'introduis d'abord un estimateur pour l'amplitude du bispectre FDI, et montre comment le combiner avec de similaires pour les sources radio et le FDC, pour une contrainte jointe des différentes sources de NG. Je quantifie la contamination des sources ponctuelles à l'estimation de NG primordiale ; pour Planck elle est négligeable aux fréquences centrales du FDC. Je décris ensuite ma mesure du bispectre FDI sur les données Planck ; il est détecté très significativement à 217, 353 et 545 GHz, avec des SNR allant de 5.8 à 28.7. Sa forme est cohérente entre les différentes fréquences, de même que l'amplitude intrinsèque de NG. Enfin, je décris ma mesure du bispectre tSZ, sur des simulations et sur les cartes tSZ estimées par Planck, validant la robustesse de l'estimation via des simulations d'avant-plans. Le bispectre tSZ est détecté avec un SNR~200. Son amplitude et sa dépendence en échelle et en configuration sont cohérentes avec la carte des amas détectés et avec les simulations. Enfin, cette mesure place une contrainte sur les paramètres cosmologiques : sigma_8 (Omega_b/0.049)^0.35 = 0.74+/-0.04 en accord avec les autres statistiques tSZ. / This PhD thesis, written in english, studies the non-Gaussianity (NG) of extragalactic foregrounds to the Cosmic Microwave Background (CMB), the latter being one of the golden observables of today's cosmology. In the last decade has emerged research for deviations of the CMB to the Gaussian law, as they would discriminate the models for the generation of primordial perturbations. However the CMB measurements, e.g. by the Planck satellite, are contaminated by several foregrounds. I studied in particular the extragalactic foregrounds which trace the large scale structure of the universe : radio and infrared point-sources and the thermal Sunyaev-Zel'dovich effect (tSZ). I hence describe the statistical tools to characterise a random field : the correlation functions, and their harmonic counterpart : the polyspectra. In particular the bispectrum is the lowest order indicator of NG, with the highest potential signal to noise ratio (SNR). I describe how it can be estimated on data, accounting for a potential mask (e.g. galactic), and propose a method to visualise the bispectrum, which is more adapted than the already existing ones. I then describe the covariance of a polyspectrum measurement, a method to generate non-Gaussian simulations, and how the statistic of a 3D field projects onto the sphere when integrating along the line-of-sight. I then describe the generation of density perturbations by the standard inflation model and their possible NG, how they yield the CMB anisotropies and grow to form the large scale structure of today's universe. To describe this large scale structure, I present the halo model and propose a diagrammatic method to compute the polyspectra of the galaxy density field and to have a simple and powerful representation of the involved terms. I then describe the foregrounds to the CMB, galactic as well as extragalactic. I briefly describe the physics of the thermal Sunyaev-Zel'dovich effect and how to describe its spatial distribution with the halo model. I then describe the extragalactic point-sources and present a prescription for the NG of clustered sources. For the Cosmic Infrared Background (CIB) I introduce a physical modeling with the halo model and the diagrammatic method. I compute numerically the 3D galaxy bispectrum and produce the first theoretical prediction of the CIB angular bispectrum. I show the contributions of the different terms and the temporal evolution of the galaxy bispectrum. For the CIB angular bispectrum, I show its different terms, its scale and configuration dependence, and how it varies with model parameters. By Fisher analysis, I show it allows very good constraints on these parameters, complementary to or better than those coming from the power spectrum. Finally, I describe my work on measuring NG. I first introduce an estimator for the amplitude of the CIB bispectrum, and show how to combine it with similar ones for radio sources and the CMB, for a joint constraint of the different sources of NG. I quantify the contamination of extragalactic point-sources to the estimation of primordial NG ; for Planck it is negligible for the central CMB frequencies. I then describe my measurement of the CIB bispectrum on Planck data ; it is very significantly detected at 217, 353 and 545 GHz with SNR ranging from 5.8 to 28.7. Its shape is consistent between frequencies, as well as the intrinsic amplitude of NG. Ultimately, I describe my measurement of the tSZ bispectrum, on simulations and on Compton parameter maps estimated by Planck, validating the robustness of the estimation thanks to realist foreground simulations. The tSZ bispectrum is very significantly detected with SNR~200. Its amplitude and its scale and configuration dependence are consistent with the projected map of detected clusters and tSZ simulations. Finally, this measurement allows to put a constraint on the cosmological parameters : sigma_8*(Omega_b/0.049)^0.35 = 0.74+/-0.04 in agreement with other tSZ statistics.