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The ionising output and gas content of galaxies

Fletcher, Thomas James; (2021) The ionising output and gas content of galaxies. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Molecular gas is the primary fuel for star formation in galaxies. Gas within giant molecular clouds collapses to form the next generation of stars. This star formation is critical in determining both how galaxies appear, via their starlight, as well as their evolution. Nowhere is this more evident than for the first generation of star-forming galaxies. These galaxies were fuelled by pristine gas, driving intense star formation, giving rise to massive stars. The starlight from these galaxies bathed the Universe with ultraviolet light, reionising the neutral hydrogen in the intergalactic medium. In this thesis we study analogues of the first galaxies, targeting Lyman continuum emission in z ∼ 3 galaxies. We determine significant individual escape fractions of ionising photons for a large sample of galaxies for the first time. However, a stack of non-detections provides a stringent upper limit on the escape fraction of < 0.5%, with no clear difference in the properties of detections and non-detections, suggesting a dichotomy in the way that Lyman continuum photons escape their host galaxy. We then use the xCOLD GASS survey to determine the molecular gas content of the local Universe more accurately than before. We calculate the ratio of molecular to atomic gas and investigate how this varies with stellar mass. Finally, we build a modular analytical model based upon empirical scaling relations. We model the SFR-M∗ plane and scaling relations between SFR and gas masses. We successfully use our model to predict the SFR distribution function, matching empirically derived results. We also use our model to predict the molecular and atomic gas mass functions, demonstrating the potential of this simple model based on observations. This thesis provides insight into the contribution of the first galaxies to reionisation, the molecular gas content of the local Universe and how scaling relations can be used to predict galaxy properties.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: The ionising output and gas content of galaxies
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2021. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/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
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI: https://discovery.ucl.ac.uk/id/eprint/10121742
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