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Genetically modified galaxies: performing controlled experiments in cosmological galaxy formation simulations

Rey, Martin Pierre; (2020) Genetically modified galaxies: performing controlled experiments in cosmological galaxy formation simulations. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

This thesis develops and applies a novel approach to studying the formation of galaxies in our Universe. Galaxies grow through gravitational amplification of early-Universe overdensities, within which gas reaches sufficient densities to trigger star formation. A galaxy's mass growth is therefore seeded randomly, originating from quantum inflationary perturbations. Understanding how this intrinsic stochasticity in histories couples with strongly non-linear astrophysics is key to interpreting the observed diversity of the galaxy population. To provide new insights to this issue, we clarify and extend the "genetic modification'' framework in Chapter 2. This approach generates alternative versions of a simulation’s initial conditions, each version with a carefully engineered change to the galaxy’s history. This in turn creates controlled experiments allowing us to construct a causal account of the galaxy's response to modifying its merger history. We introduce a new class of variance modifications aiming at improving control over several mergers. We then evolve these variance-modified initial conditions using the simulation code RAMSES, first studying dark matter halo formation (Chapter 3). We causally recover the known correlation between halo formation time and concentration when modifying the merger histories of two haloes, and further establish how late major mergers determine concentrations at fixed formation time. We then turn to the formation of ultra-faint dwarf galaxies with high-resolution hydrodynamical simulations. Scanning through histories, we demonstrate that earlier forming ultra-faints have higher stellar mass today and predict a new class of highly diffuse ultra-faint galaxies which assemble through late mergers (Chapter 4). We finally use a larger suite of objects (Chapter 5) to show how ultra-faints growing sufficiently in dynamical mass after reionization can accrete gas and re-ignite star formation. We conclude that, by transforming cosmological histories into tuneable parameters, "genetically modified'' experiments generate new insights on the complexity of dark matter halo and galaxy formation.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Genetically modified galaxies: performing controlled experiments in cosmological galaxy formation simulations
Event: UCL
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: © The Author 2020. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10089039
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