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
The intracluster medium (ICM) is a hot, tenuous and X-ray emitting gas that pervades galaxy clusters. Meanwhile, extended synchrotron sources, i.e., radio relics and radio halos are frequently... Show moreThe intracluster medium (ICM) is a hot, tenuous and X-ray emitting gas that pervades galaxy clusters. Meanwhile, extended synchrotron sources, i.e., radio relics and radio halos are frequently observed in galaxy cluster, for which the two widely accepted particle acceleration are shock acceleration and turbulent acceleration, respectively. Both of these scenarios are due to ICM motions, which means that X-ray observations of the ICM are fundamental for quantifying shock wave and turbulence properties to test the acceleration models. This thesis focuses on X-ray observations of galaxy clusters, and covers topics from ICM shock - radio relic connection to turbulence - radio halo connection. The new observational evidences further support the two acceleration scenario. 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
Roberts, I.D.; Lang, M.; Trotsenko, D.; Bemis, A.R.; Ellison, S.L.; Lin, L.; ... ; Weeren, R.J. van 2022
In this thesis, I studied the origin and evolution of the non-thermal radiation in merging galaxy clusters. Cluster mergers are the among the most energetic events in the Universe. Part of this... Show moreIn this thesis, I studied the origin and evolution of the non-thermal radiation in merging galaxy clusters. Cluster mergers are the among the most energetic events in the Universe. Part of this energy is released in turbulence and shock waves which can (re-)accelerate cosmic rays and amplify magnetic fields in the intra-cluster medium (ICM). The interaction of these results in large-scale synchrotron radiation, which is visible through radio observations. In addition, X-ray observations of the ICM were carried out to investigate the dynamical state of the clusters, and the properties of cluster shocks. Show less
Di Gennaro, G.; Weeren, R.J. van; Rudnick, L.; Hoeft, M.; Brüggen, M.; Ryu, D.; ... ; Hoang, D.N. 2021
It has now been well established that shocks and turbulent motions in the intra-cluster medium (ICM) generated through cluster mergers can produce large-scale synchrotron emission. However, the... Show moreIt has now been well established that shocks and turbulent motions in the intra-cluster medium (ICM) generated through cluster mergers can produce large-scale synchrotron emission. However, the underlying particle acceleration mechanisms responsible for the origin of these faint diffuse radio sources are not well understood. With the advent of new generation low-frequency radio telescopes and better calibration techniques it has now become possible to unveil low-frequency radio sky with unprecedented depth and sensitivity, that is full of potential for new discoveries. The first part of this dissertation presents the study to better understand the nature of revived fossil (radio) plasma sources in galaxy cluster and establish them as a distinct class of radio sources. The complexity of objects, observed with these new instruments are just tip of the iceberg of the population, and will challenge the traditional taxonomy of diffuse radio sources. The last part of the dissertation focuses on deriving the deepest radio source-counts at 150 MHz. This is one of the several cosmological tests to check feasibility of new cosmological models and a sanity check for the data reduction. The derived source-counts are also compared with the other existing determinations, as well as with state-of-the-art evolutionary models. Show less
In this thesis, I study the formation of large-scale structure and the physics of particle acceleration at large scales (~Mpc). The object of my study is clusters of galaxies that are... Show moreIn this thesis, I study the formation of large-scale structure and the physics of particle acceleration at large scales (~Mpc). The object of my study is clusters of galaxies that are in the formation process. Galaxy clusters form through a sequence of mergers of sub-clusters. During the formation of galaxy clusters, shocks and turbulence are generated in the intra-cluster medium (ICM). These shocks and turbulence (re-)accelerate cosmic ray (CR) particles to relativistic speeds. In the presence of magnetic fields, the CR particles emit synchrotron radiation that we can observe with radio telescopes. I also combine radio data with X-ray and optical data to study these clusters. Studies of these merging galaxy clusters help us to understand the physics of particle acceleration at cosmic scales Show less
