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Following the collapse and evolution of cosmological structures in simulations

Abstract : Observational efforts during the last decades have led to the establishment of the ΛCDM model as the standard model of our Universe. In this model, dark matter represents the majority of the matter content of the Universe, whose unknown nature poses one of the largest mysteries in physics today. A key ingredient for constraining its properties and physical origin from astronomical observations is the modeling of dark matter in cosmological simulations to understand the formation of structures and create accurate predictions. In this thesis, we study various aspects of the gravitational collapse of perturbations in the initial density field, which leads to an intricate web composed of walls, filaments, and halos, in which baryons condense and form the rich structures that we can observe today. In particular, we use cosmological Nbody simulations and exploit the Lagrangian mapping from coordinates in the initial conditions to the late time positions and velocities to follow the evolution of the dark matter fluid. In a first part, we use the phase-space properties of dark matter to study the emergence of the largescale velocity dispersion tensor field. It carries the anisotropic signature of gravitational collapse, allowing us to derive a new classification method of the cosmic web and characterize the velocity field of dark matter in these collapsed environments. We then show that the amplitude of the dark matter velocity dispersion is in good agreement with the isotropic random velocities in the shock-heated baryonic gas tracing the dark matter distribution. This will allow improved predictions of temperatures of the intergalactic medium from N-body simulations in future studies. In a second part, we focus on the collapse of gravitationally bound halos and their origin in the initial perturbation field. These proto-halo patches play an important role for zoom simulations, i.e. simulations that focus computational resources on an individual object of interest and thus require accurate knowledge about the Lagrangian patch from where the object forms. In this regard, we develop a web application, which allows users to find target objects for re-simulation in various halo catalogs of existing state-of-the-art simulations, to retrieve initial conditions for different simulation codes refined on their associated proto-halo, and to reference the initial conditions in scientific publications. Finally, we exploit the available dataset of halos and associated proto-halos to study the connection between the initial perturbations, intrinsic properties of the collapsed objects, and the influence of the large scale environment.
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Submitted on : Friday, May 29, 2020 - 9:48:10 AM
Last modification on : Monday, October 12, 2020 - 11:10:20 AM


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  • HAL Id : tel-02648529, version 1



Michael Bühlmann. Following the collapse and evolution of cosmological structures in simulations. Cosmology and Extra-Galactic Astrophysics [astro-ph.CO]. COMUE Université Côte d'Azur (2015 - 2019), 2019. English. ⟨NNT : 2019AZUR4064⟩. ⟨tel-02648529⟩



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