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

Preview

Text Rey_10089039_thesis.pdf - Submitted Version Download (3MB) | Preview

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.

Download activity - last month

Export as CSVXMLJSON

Download activity - last 12 months

Export as JSONXMLCSV

Downloads by country - last 12 months

Export as JSONCSVXML

Archive Staff Only

View Item