Finding the needle in the haystack: 21 cm cosmology in the midst of foregrounds
File(s)
Author(s)
Hothi, Iandeep
Type
Thesis
Abstract
Epoch of Reionization (EoR) represents the last major phase change in the Universe. Here, radiation from the first sources carved out ionized bubbles around them, which grew until the bubbles merged - slowly ionizing the Intergalactic Medium (IGM). This epoch gives rise to the Universe we see today but is a 1 billion-year period we know very little about. We have indirect constraints from the CMB and spectra of high redshift quasars that give up loose timing constraints but leave fundamental questions unanswered. The hydrogen during this epoch emits a weak hyperfine transition line, a photon with a wavelength of 21cm - giving us a direct probe into this important epoch.
Several radio interferometers are looking to measure this 21cm signal, providing statistics that will allow us to answer fundamental questions about this epoch. Sadly, the signal we observed is contaminated with foregrounds that are orders of magnitude stronger than the 21cm signal we wish to observe. These foregrounds come from our own galaxy in the form of synchrotron and free-free emission from diffuse clouds as well as from extra-galactic sources.
In this Thesis, we aim to understand these foregrounds and utilise techniques to mitigate them. Allowing for 21 cm Cosmology In The Midst of
Foregrounds. We first start by applying these techniques to real data and forward model observations to better understand the performance and limitations of the different techniques. We then see how these techniques perform on higher-order statistics and if we can recover the statistic from observations. We then look to potential synergies between large-scale galaxy surveys and interferometers to see if we can understand the end of the EoR better and use these synergies for foreground mitigation. We finally focus on removing bright sources in our sky and how improving models of these bright sources will allow us to better recover the 21cm signal from the EoR.
Several radio interferometers are looking to measure this 21cm signal, providing statistics that will allow us to answer fundamental questions about this epoch. Sadly, the signal we observed is contaminated with foregrounds that are orders of magnitude stronger than the 21cm signal we wish to observe. These foregrounds come from our own galaxy in the form of synchrotron and free-free emission from diffuse clouds as well as from extra-galactic sources.
In this Thesis, we aim to understand these foregrounds and utilise techniques to mitigate them. Allowing for 21 cm Cosmology In The Midst of
Foregrounds. We first start by applying these techniques to real data and forward model observations to better understand the performance and limitations of the different techniques. We then see how these techniques perform on higher-order statistics and if we can recover the statistic from observations. We then look to potential synergies between large-scale galaxy surveys and interferometers to see if we can understand the end of the EoR better and use these synergies for foreground mitigation. We finally focus on removing bright sources in our sky and how improving models of these bright sources will allow us to better recover the 21cm signal from the EoR.
Version
Open Access
Date Issued
2022-08
Date Awarded
2022-11
Copyright Statement
Creative Commons Attribution NonCommercial NoDerivatives Licence
Advisor
Chapman, Emma
Pritchard, Jonathan
Sponsor
Royal Society (Great Britain)
Grant Number
638743-FIRSTDAWN
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)