PUMA and MAJICK: cross-matching and imaging techniques for a detection of the epoch of reionisation

Abstract

The epoch of reionisation (EoR) is one of the last unknowns in observational cosmology. After recombination, when the Universe cooled sufficiently and collapsed into neutral hydrogen (HI), the Universe was devoid of any light sources. During this cosmic ‘dark age’, the Universe was completely opaque to ultra-violet radiation, due to the abundance of HI. After some time, the very first luminous sources formed via gravitational collapse, and began to ionise the surrounding HI. Eventually the Universe transitioned from opaque to transparent, allowing us once again to peer into the cosmic depths. The exact timing and manner of the EoR has never been observed, and is paramount to confirming our the wealth of theoretical understanding. A new generation of low radio-frequency interferometers have opened a window to explore the EoR, by tracing the evolution of 21 cm radiation from HI. The experiment hinges upon our ability to remove astrophysical foregrounds; extragalactic radio-loud galaxies and galactic diffuse synchrotron emission all conspire to drown out the EoR signal.

In the first part of this thesis, we develop a new cross-matching method in order to create the most accurate radio source foreground model possible. We go on to apply this technique to catalogue creation and verification, and investigate the effects of accurate source positions in foreground removal. We comment on how this technique can inform next generation instrument design, such as the upcoming instrument SKA_LOW. In the second part, we investigate averaging interferometric data as a potential method to reduce both the enormous data loads that interferometers produce, and the contamination caused by far-field sources. Averaging inherently causes signal loss, with the amplitude of the loss dependent on the scale and layout of the telescope, and so its impact on a potential EoR measurement must be well understood. We develop simulation and imaging software with new functionality to achieve this.