Cosmic microwave background observations for large-scale structure studies

Overview & Synopsis

The large-scale structure of the Universe is organized through dark matter halos and filaments. These halos and filaments are also the regions where baryonic matter tends to reside, under the form of gas or as stars in galaxies. This thesis studies the joint distributions of dark matter, gas and galaxies thanks to the cross-correlation formalism. According to General Relativity, spacetime is distorted by the presence of matter, so that photons from the cosmic microwave background are deflected along their path towards us. This effect, known as gravitational lensing, makes it possible to directly measure the dark matter distribution in the Universe. Similarly, during their propagation towards us, photons from the cosmic microwave background travel through hot gas in galaxy clusters and interact with the electrons which let an imprint on the frequency of the photon. This is the so-called thermal Sunyaev-Zeldovich effect and is a way of probing the gas distribution in the Universe. As for wide and deep galaxy surveys, they reveal how galaxies are distributed on large scales. In this thesis, observations of the cosmic microwave background gravitational lensing, of the thermal Sunyaev-Zeldovich effect and of the galaxy distribution are used together in order to get a more comprehensive understanding of the large-scale structure of the Universe as well as the interactions between dark matter, gas and galaxies. In a second part, observations of the galaxy distribution and of the cosmic microwave background gravitational lensing are used to test modified gravity models which can explain the accelerated expansion of the Universe. In particular, I place constraints on a specific model of f(R) gravity and show that the use of cross-correlations between the cosmic microwave background lensing and the galaxy distribution is essential. Indeed, this cross-correlation can break the degeneracy between the galaxy bias and the way gravity impacts the galaxy power spectrum. Finally, this thesis prepares the data exploitation of the Euclid mission. When performing a galaxy survey, a limited volume of the Universe is observed but modes with a wavelength larger than the size of the survey can impact the way galaxies are distributed in the considered volume. In order not to bias the findings, the impact of these large modes must be taken into account, which is done through the so-called "Super Sample Covariance". In this thesis, I study the impact of this covariance on the cosmological constraints that will be obtained using the cross-correlations between Euclid's observations and the cosmic microwave background gravitational lensing measured by future missions.