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• W2964679927 abstract "This thesis is the result of a PhD project that tried to investigate and find new descriptions of entities arising in large scale structure based upon their spatial configuration. For this we analyse N-body simulations of gravitational collapse in a cold dark matter universe with cosmological constant (ΛCDM) and Monte Carlo ray-tracing radiative transfer (MCRTRT) simulations of reionisation. We also use an N-body simulations to investigate possible problems with observational results connected to large scale clustering. In the first part of this thesis we develop a novel technique to characterise the density field in cosmological N-body simulations based upon a density estimate and the connectivity between particles obtained from a Voronoi tessellation of their positions. We use this estimate to find a hierarchical set of peaks in the Millennium and Millennium II simulations. This hierarchy completely decomposes the particle load of the simulations into nodes in a single tree structure we call “Tessellation Level Tree” (TLT). We investigate the properties of these peaks and concentrate on two novel aspects: the percolation of the connected set of peaks above densities of a few (6 − 7) along the cosmic web and the very strong assembly bias effect if peaks are split by saddle point density. This assembly bias effect is the strongest ever obtained from quintiles in a local property of the dark matter distribution in simulations. The second part of the thesis investigates the morphology of ionised bubbles in hydrogen and helium during reionisation. For this we use MCRTRT on regular grids and create binary representations of the ionisation fields using a threshold. We then apply techniques of mathematical morphology to extract a hierarchy of bubbles ordered by local diameter. We show the shift in the global bubble size distribution throughout reionisation and how the ionised volume is more and more unequally distributed among the bubbles as they grow and overlap. The overlap also results in a percolation process we identify at z ≳ 8 that increasingly delocalises the reionisation process. Finally, we connect the bubbles to the properties of the underlying density field. For the first time we show that the largest bubbles in the post-overlap regime are not densest in the centre are very strongly biased with respect to the large scale matter distribution. We also quantify how ionisation reaches the most underdense parts of the universe last, reconfirming the inside-out scenario of reionisation. In the final part of the thesis we test the assembly bias and splashback radius mea- surements claimed by previous publications using clusters obtained with the optical cluster finder redMaPPer. For this we develop a mock-version of the algorithm that incorporates the core aspects of the cluster identification and apply it to a semi-analytic galaxy popula- tion of the Millennium simulation. We show that the claimed concentration differences in the optically selected clusters are most likely stemming from projection effects that arise more in overdense regions, leading to a coupling between concentration and large scale clustering and therefore a false positive assembly bias detection. The claimed splashback radius identification that is inverse in connection with cluster properties compared to the results of numerical simulations is shown to be an artifact of the circular mask of the selection algorithm." @default.
• W2964679927 created "2019-08-13" @default.
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• W2964679927 date "2019-06-28" @default.
• W2964679927 modified "2023-09-27" @default.
• W2964679927 title "Spatial description of large scale structure and reionisation" @default.
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