Three major cosmology-focused missions are planned for the next decade: the Euclid space telescope, the Vera C. Rubin Observatory in Chile, and the Nancy Grace Roman Space Telescope. Their surveys... Show moreThree major cosmology-focused missions are planned for the next decade: the Euclid space telescope, the Vera C. Rubin Observatory in Chile, and the Nancy Grace Roman Space Telescope. Their surveys will detect billions of galaxies over more than a third of the celestial sphere and out to redshifts of z~2 to constrain the evolving matterdistribution using weak gravitational lensing. This thesis focusses on ways of disentangling the contribution of normal matter, baryons for cosmologists, from the measured weak lensing signal for cosmic shear analyses and galaxy cluster mass calibrations. Combining the predictions of computer-simulated universes, evolving billions of particles in time, with simplified models that reproduce the observeddistribution of hot gas inside clusters of galaxies, but that freely vary the amount of matter where no observations are available, we have quantified how strongly our ignorance of the relation between ordinary and dark matter will affect the analysis of the planned surveys. Additionally, we have studied how baryons affect cluster massdeterminations and we suggest a new analysis method for cluster abundance studies that is less sensitive to our lack of knowledge of the exact distribution of normal matter in the outskirts of galaxy clusters. Show less
At the largest scales, two ingredients dictate the distribution of matter in the Universe. The first is dark matter, acting as an invisible scaffolding held together by gravitational forces. The... Show moreAt the largest scales, two ingredients dictate the distribution of matter in the Universe. The first is dark matter, acting as an invisible scaffolding held together by gravitational forces. The second is dark energy, an enigmatic component responsible for the accelerated expansion of the Universe. Under these two forces, matter in the Universe organizes itself in the so-called cosmic web. The nodes of this network are large dark matter haloes, and this thesis explores how their boundaries provide information about the nature of dark energy and cosmology. Chapters 3 and 4 present robust theoretical predictions for this titular edge and discuss its simple physical interpretation. Chapters 2 and 5 corroborate these results by presenting measurements of this feature in weak-lensing data. The last scientific chapter of this thesis is a collection of studies in gravitational-wave physics. This chapter explores how these spacetime ripples observed from across the cosmos can be used to detect alternative theories of gravity. Show less
In this thesis, the research focuses on the properties of dark matter and dark matter haloes and how they connect with the galaxies we can observe in the Universe. Because of the still unknown... Show moreIn this thesis, the research focuses on the properties of dark matter and dark matter haloes and how they connect with the galaxies we can observe in the Universe. Because of the still unknown nature of dark matter, we tend to study it using the properties of its distribution and its properties on galactic scales and beyond. The galaxy–dark matter connection is important for three main reasons, and understanding it helps with answering the largest questions in astrophysics and cosmology today. First question includes the understanding of the physics of galaxy formation. Secondly, the inference of cosmological parameters – if we want to robustly measure the cosmological parameters, we have to understand, how the galaxies interplay with the dark matter, and thirdly, the inference of evolution of matter distribution and properties of dark matter. We explore different aspects of the galaxy–dark matter connection that can be measured using gravitational lensing, more specifically, using galaxy-galaxy lensing as our primary probe. We use the halo model together with the halo occupation distributions to statistically describe the galaxy-halo connection and to constrain assembly bias in rich galaxy groups. The same theoretical framework is also used to constrain the nature of galaxy bias. Show less
Improvements of weak gravitational lensing shape measurements are presented and some used for data analysis. Accurate estimates of masses are calculated for clusters of galaxies and member... Show moreImprovements of weak gravitational lensing shape measurements are presented and some used for data analysis. Accurate estimates of masses are calculated for clusters of galaxies and member galaxies. Show less
Our Universe is comprised not only of normal matter but also of unknown components: dark matter and dark energy. This Thesis recounts studies of dark matter haloes, using a technique known as weak... Show moreOur Universe is comprised not only of normal matter but also of unknown components: dark matter and dark energy. This Thesis recounts studies of dark matter haloes, using a technique known as weak gravitational lensing, in order to learn more about the nature of these dark components. The haloes analysed are both those surrounding individual galaxies and those encompassing massive galaxy clusters. In order to better study these haloes, new lensing software is developed and existing lensing theory is advanced in the context of this Thesis. As a result, new higher-order signals are detected and lenses are studied in greater detail than ever before. Show less
In my thesis I study the projected density distribution of all (dark+baryonic) matter around various selections of galaxies and galaxy clusters in the Red-sequence Cluster Survey 2 (RCS2), one of... Show moreIn my thesis I study the projected density distribution of all (dark+baryonic) matter around various selections of galaxies and galaxy clusters in the Red-sequence Cluster Survey 2 (RCS2), one of the largest optical imaging surveys to date. This is done by measuring the tiny distortions in the images of background galaxies induced by the gravitational potential of the foreground objects, which are called the lenses. Comparing this so-called weak gravitational lensing signal to model predictions enables us to determine the total mass of the lenses. We study how the total mass relates to, amongst others, the luminosity of the lenses, and to the total mass in stars, which leads to valuable insight into galaxy formation processes. We also study the anisotropy of the weak lensing signal around galaxies, to constrain the average ellipticity of the dark matter haloes in which these galaxies are embedded. Finally, we measure the relation between the total mass of galaxy clusters and the number of cluster members, and how this relation changes with redshift. This is essential for using cluster counts to constrain cosmological parameters, but also contains information of how clusters form. Show less
