Hamza El Bouhargani

La reconstruction de cartes de haute fidélité du ciel micro-ondes à partir des données d'expériences multi-kilo pixels pour la cosmologie de haute précision.: Durant les deux dernières décennies, la cosmologie a été propulsée par de nombreux développements théoriques et expérimentaux lui permettant d'entrer dans l'ère de la haute précision. De nouvelles expériences sont actuellement en cours de préparation pour débuter leurs opérations dans les prochaines années et continuer de pousser les frontières du savoir et améliorer notre compréhension théorique des rouages internes de l'Univers. En particulier, la prochaine génération d'observatoires du fond diffus cosmologique (Cosmic Microwave Background - CMB) permettra la cartographie des anisotropies de température et de polarisation du CMB avec une précision inédite, sur des échelles allant du degré sur le ciel jusqu'aux minutes d'arc. Ces observatoires vont ainsi ouvrir une fenêtre unique sur l'Univers primordial ainsi que sur son évolution récente. Ces mesures contiennent des informations clés sur la nature de la matière noire, l'énergie noire, ainsi que la physique des neutrinos, et pourraient également révéler l'existence des ondes gravitationnelles primordiales, qui seraient générées durant la phase inflationnaire à des énergies proches de l'échelle des théories de grande unification aux premiers instant de l'Univers. Atteindre ces ambitieux objectifs scientifiques nécessite la construction d'expériences d'une complexité exceptionnelle. Les signaux extrêmement faibles qu'on tente de mesurer requièrent de très grandes sensibilités, et donc la collection de volumes énormes de données, ainsi qu'un contrôle précis des effets systématiques. Ceci rend l'analyse et l'exploitation scientifique des données particulièrement difficile sur le plan, à la fois, computationnel et méthodologique. Le travail présenté dans cette thèse se donne pour objectif de s'attaquer à ces problèmes dans les premières étapes de l'analyse où l'on traite tout le volume des données dans le domaine temporel. Je généralise la procédure de cartographie afin de permettre une mitigation efficace de certains des effets systématiques majeurs dans le domaine temporel simultanément avec l'estimation non biaisée des cartes du ciel. J'aborde à la fois les problèmes computationnels et méthodologiques, posés lors du développement d'observatoires du CMB au sol de type "stage-3" comme Simons Array et Simons Observatory, en développant un environnement massivement parallèle testé et validé sur des supercalculateurs à l'état de l'art mondial. L'environnement offre des méthodes robustes pour la résolution du problème de cartographie en cas de présence de nombreux effets systématiques dans le domaine temporel, qui doivent être modélisés avec une précision suffisante pour permettre une mesure robuste des signaux cosmologiques d'intérêt comme les modes-B issus des ondes gravitationnelles produites lors de l'inflation.

We present updated forecasts for the scientific performance of the degree-scale (0.5 deg FWHM at 93 GHz), deep-field survey to be conducted by the Simons Observatory (SO). By 2027, the SO Small Aperture Telescope (SAT) complement will be doubled from three to six telescopes, including a doubling of the detector count in the 93 GHz and 145 GHz channels to 48,160 detectors. Combined with a planned extension of the survey duration to 2035, this expansion will significantly enhance SO's search for a B -mode signal in the polarisation of the cosmic microwave background, a potential signature of gravitational waves produced in the very early Universe. Assuming a 1/ f noise model with knee multipole ℓ _knee = 50 and a moderately complex model for Galactic foregrounds, we forecast a 1 σ (or 68% confidence level) constraint on the tensor-to-scalar ratio r of σ _r = 1.2 × 10 ^-3 , assuming no primordial B-modes are present. This forecast assumes that 70% of the B -mode lensing signal can ultimately be removed using high resolution observations from the SO Large Aperture Telescope (LAT) and overlapping large-scale structure surveys. For more optimistic assumptions regarding foregrounds and noise, and assuming the same level of delensing, this forecast constraint improves to σ _r = 7 × 10 ^-4 . These forecasts represent a major improvement in SO's constraining power, being a factor of around 2.5 times better than what could be achieved with the originally planned campaign, which assumed the existing three SATs would conduct a five-year survey.

We report a measurement of the E-mode polarization power spectrum of the cosmic microwave background (CMB) using 150 GHz data taken from 2014 July to 2016 December with the Polarbear experiment. We reach an effective polarization map noise level of - across an observation area of 670 square degrees. We measure the EE power spectrum over the angular multipole range , tracing the third to seventh acoustic peaks with high sensitivity. The statistical uncertainty on E-mode bandpowers is ∼2.3 at , with a systematic uncertainty of 0.5 . The data are consistent with the standard ΛCDM cosmological model with a probability-to-exceed of 0.38. We combine recent CMB E-mode measurements and make inferences about cosmological parameters in ΛCDM as well as in extensions to ΛCDM. Adding the ground-based CMB polarization measurements to the Planck data set reduces the uncertainty on the Hubble constant by a factor of 1.2 to . When allowing the number of relativistic species ( ) to vary, we find , which is in good agreement with the standard value of 3.046. Instead allowing the primordial helium abundance ( ) to vary, the data favor . This is very close to the expectation of 0.2467 from big bang nucleosynthesis. When varying both and , we find and .

We present a measurement of the B-mode polarization power spectrum of the cosmic microwave background (CMB) using data taken from 2014 July to 2016 December with the Polarbear experiment. The CMB power spectra are measured using observations at 150 GHz with an instantaneous array sensitivity of on a 670 square degree patch of sky centered at (R.A., decl.) = (+0^h12^m0^s, −59°18′). A continuously rotating half-wave plate is used to modulate polarization and to suppress low-frequency noise. We achieve 32 μK arcmin effective polarization map noise with a knee in sensitivity of ℓ = 90, where the inflationary gravitational-wave signal is expected to peak. The measured B-mode power spectrum is consistent with a ΛCDM lensing and single dust component foreground model over a range of multipoles 50 ≤ ℓ ≤ 600. The data disfavor zero at 2.2σ using this ℓ range of Polarbear data alone. We cross-correlate our data with Planck full mission 143, 217, and 353 GHz frequency maps and find the low-ℓ B-mode power in the combined data set to be consistent with thermal dust emission. We place an upper limit on the tensor-to-scalar ratio r < 0.90 at the 95% confidence level after marginalizing over foregrounds.

We present a measurement of the gravitational lensing deflection power spectrum reconstructed with two seasons of cosmic microwave background polarization data from the Polarbear experiment. Observations were taken at 150 GHz from 2012 to 2014 and surveyed three patches of sky totaling 30 square degrees. We test the consistency of the lensing spectrum with a cold dark matter cosmology and reject the no-lensing hypothesis at a confidence of 10.9σ, including statistical and systematic uncertainties. We observe a value of A _L = 1.33 ± 0.32 (statistical) ±0.02 (systematic) ±0.07 (foreground) using all polarization lensing estimators, which corresponds to a 24% accurate measurement of the lensing amplitude. Compared to the analysis of the first-year data, we have improved the breadth of both the suite of null tests and the error terms included in the estimation of systematic contamination.

We report a 4.8σ measurement of the cross-correlation signal between the cosmic microwave background (CMB) lensing convergence reconstructed from measurements of the CMB polarization made by the Polarbear experiment and the infrared-selected galaxies of the Herschel-ATLAS survey. This is the first measurement of its kind. We infer a best-fit galaxy bias of , corresponding to a host halo mass of at an effective redshift of z ∼ 2 from the cross-correlation power spectrum. Residual uncertainties in the redshift distribution of the submillimeter galaxies are subdominant with respect to the statistical precision. We perform a suite of systematic tests, finding that instrumental and astrophysical contaminations are small compared to the statistical error. This cross-correlation measurement only relies on CMB polarization information that, differently from CMB temperature maps, is less contaminated by galactic and extragalactic foregrounds, providing a clearer view of the projected matter distribution. This result demonstrates the feasibility and robustness of this approach for future high-sensitivity CMB polarization experiments.