Meyer, Romain A.;
(2020)
The Role of Galaxies and Quasars in Reionising the High Redshift Intergalactic Medium.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
Only one billion years after the Big Bang, the neutral hydrogen in the intergalactic medium had been completely ionised. This last phase transition of the Universe known as the epoch of reionisation is one of the frontiers in astrophysics. Despite our growing knowledge on the timing and topology of cosmic reionisation, the sources responsible for emitting the necessary ionising photons have remained elusive. Specifically, the escape fraction of ionising photons in reionisation-era galaxies and the role of quasars remain open and debated questions. This Thesis aims to answer these questions in order to understand the nature of the sources of reionisation. Firstly, I present the discovery of a luminous galaxy whose double-peak Lyman-α emission profile indicates an escape fraction close to 100%. I show how this galaxy is the first evidence of an object self-ionising its own H II bubble deep into the reionisation era. Secondly, I measure the cross-correlation of z ∼ 5-6 galaxies and metal absorbers with the IGM opacity to Lyman-α probed by high-redshift quasars. I extend the analytical model of the galaxy-IGM cross-correlation to derive average escape fractions for faint galaxies in the reionisation era. Thirdly, I investigate the evolution of quasars with redshift by measuring the relative offsets of broad emission lines in four hundred quasars at 1 < z < 7. I discuss how quasar evolution and selection biases can explain the increased blueshift of the triplyionised carbon (C IV) quasar broad emission line in the first billion years. I then present the first results of a programme to detect missing lensed z ∼ 6 quasars. Finally, this Thesis concludes on the combination of the different results into a coherent picture of the nature of the sources of reionisation and prospects for future instruments and surveys.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | The Role of Galaxies and Quasars in Reionising the High Redshift Intergalactic Medium |
| Event: | UCL (University College London) |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2020. 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. |
| Keywords: | astrophysics, astronomy, galaxies, reionisation |
| 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/10112095 |
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