Low-order multipoles and the Global 21-cm signal
File(s)
Author(s)
Ignatov, Yordan
Type
Thesis
Abstract
The early Universe, characterized by the Cosmic Microwave Background (CMB), and the late Universe, thoroughly probed by extensive galaxy surveys, are both remarkably well-measured. Yet, no direct probes of the intervening period have been detected, in which primordial hydrogen collapsed to form the first stars and galaxies. The 21-cm signal stands as an excellent potential tracer of this period, and is formed by the absorption and emission of 21-cm photons when the CMB interacts with neutral hydrogen in the early Universe. Detecting this signal would provide constraints on the timings and properties of first stellar formation, and the reionization of the Universe.
The 21-cm signal is very faint, and is set against much brighter foreground emission from the Milky Way and other galaxies. The search for the sky-averaged ``global'' signal is carried out by numerous radio antenna experiments. A large number of factors hinder this detection, such as chromatic beams, instrumental calibration errors and ionospheric effects, all of which threaten to wash out the signal or lead to false signal shapes being inferred. These effects must be taken into account when modelling the foregrounds and signal in experiment data.
The 21-cm signal is very faint, and is set against much brighter foreground emission from the Milky Way and other galaxies. The search for the sky-averaged ``global'' signal is carried out by numerous radio antenna experiments. A large number of factors hinder this detection, such as chromatic beams, instrumental calibration errors and ionospheric effects, all of which threaten to wash out the signal or lead to false signal shapes being inferred. These effects must be taken into account when modelling the foregrounds and signal in experiment data.
Version
Open Access
Date Issued
2025-06-17
Date Awarded
01/12/2025
License URL
Advisor
Pritchard, Jonathan
Sponsor
Science and Technology Facilities Council (Great Britain)
Grant Number
ST/W507519/1
Publisher Department
Department of Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)