Over the years, the development of large-scale structure simulations has given us more and more cluster samples from which we can infer cosmological information via cluster counts. As a matter of...Show moreOver the years, the development of large-scale structure simulations has given us more and more cluster samples from which we can infer cosmological information via cluster counts. As a matter of fact, we can use this probes to constraint some cosmological parameters like the matter density Ωm or the amplitude of density fluctuations at 8 Mpc h−1, σ8. However, this kind of data analysis is heavily affected by systematic errors of astrophysical kind. A recent proxy has been proposed to overcome this difficulties: the cluster sparsity, defined as the ratio of different halo mass definitions. In this thesis we will test this observable on the halo catalogue of the new simulation FLAMINGO, studying its property in a fullhydrodynamics simulation for the first time. We will test its dependence on different cosmologies, showing that the effects of baryonic matter are almost an order of magnitude higher than the differences between two valid cosmologies (in this case Planck-18 and DES). Finally, we will use the hot gas particles included in FLAMINGO to perform a mock X-ray measurement of the sparsity in order to predict the systematics that could affect a real-life observation. We find that indeed a significant bias affects the halo mass, while the sparsity is way less biased and is actually compatible with accurate values extracted from the simulation. We conclude that the sparsity does seem as a reliable and effective proxy for cosmological constraints.Show less
The Standard model of particle physics is extremely successful in explaining accelerator data. However, it is incomplete and fails to resolve several phenomena known as beyond the Standard model ...Show moreThe Standard model of particle physics is extremely successful in explaining accelerator data. However, it is incomplete and fails to resolve several phenomena known as beyond the Standard model (BSM) problems. The BSM problems may be solved by introducing new particles. In addition to particle experiments, cosmological observation offers a way we can put limits on the parameters of these new particles. This work gives a detailed qualitative description of several such cosmological constraints. The observations used are described, and then ways in which new particles could impact such observations. Then, these constraints are applied to two case studies: the scalar portal and the neutrino portal. In both cases, a significant part of the parameter space unexplored by direct experimental studies can be excluded based on these cosmological arguments.Show less
After a short introduction on the history of dark matter research, we review the current state of knowledge on both dark matter and sterile neutrinos, motivating sterile neutrinos as a dark matter...Show moreAfter a short introduction on the history of dark matter research, we review the current state of knowledge on both dark matter and sterile neutrinos, motivating sterile neutrinos as a dark matter candidate. We then investigate the dependence of current constraints on the sterile neutrino parameter space on the fraction $\chi_N$ of the dark matter mass density that is due to sterile neutrinos, and derive a lower bound on the fraction assuming the 3.5 keV spectral line detected in galaxies and galaxy clusters is caused by sterile neutrino decay: $\chi_N \gtrsim 0.1$.Show less
We will show the weak lensing effects from filaments connecting galaxy pairs for two separate galaxy subsets. The lensing galaxies are selected from the Galaxy And Mass Assembly (GAMA) survey,...Show moreWe will show the weak lensing effects from filaments connecting galaxy pairs for two separate galaxy subsets. The lensing galaxies are selected from the Galaxy And Mass Assembly (GAMA) survey, where we use version 7 of the GAMA galaxy group catalogue in our galaxy selection. We select the background galaxies from the ’KiDS-450’ weak lensing data set. Two galaxies are considered to form a pair when they are within an angular separation of 6h^-1 Mpc and 10h^-1 Mpc and are within a line of sight separation of 10h^-1 Mpc. In addition, we select galaxies with an angular separation between 6h^-1 Mpc and 10h^-1 Mpc, with a line of sight separation between 100h^-1 Mpc and 120h^-1 Mpc, to be ’unphysical pairs’. They appear to be galaxy pairs projected on the sky but are physically to far separated to form a pair. The subtraction of the signal of the unphysical pairs from the physical pairs will then result in the isolation of the filament. We use two subsets of galaxies in our pair selection; galaxies isolated in space, and the central galaxies of galaxy groups with at least 4 group members and consider the lensing effects of both subsets. Using 25 000 and 8 279 galaxy pairs from the isolated galaxy pairs subset and group central galaxy pair subset respectively, we will show the detection of filaments with a significance of 2.3\sigma and 2.9\sigma for these subsets.Show less
