Compressive Faraday Imaging for Next-Generation Radio Telescopes

Abstract

Over the past decade radio astronomy has grown considerably. Next-generation radio telescopes have pushed the boundaries of what is possible scientifically. Furthermore, the advent of broadband polarisation measurements with modern radio telescopes have enabled the investigation of the origin and evolution of magnetic fields using the RM Synthesis technique. This technique is based on the fact that there is Fourier relationship between polarized intensity (corrected by the spectral dependency) as a function of wavelength-squared and the Faraday dispersion function. However, the reconstruction of Faraday depth structures from incomplete spectral polarisation radio measurements is an under-constrained problem that requires additional regularisation. In this thesis, a compressed sensing framework for Faraday imaging named cs-romer along with a method to select the optimal basis/wavelet given the data are proposed. The framework is demonstrated on a variety of simulated scenarios and observational configurations. Additionally, cs-romer is demonstrated on real data from the JVLA and MeerKAT telescopes. The results of a JVLA analysis on the Abell 1314 cluster show that individual galaxies within Abell 1314 deviate from the behaviour expected for a Faraday-thin screen such as the intra-cluster medium and instead suggest that the Faraday rotation exhibited by these galaxies is dominated by their local environments. For MeerKAT we use the framework on the COSMOS field, showing that cs-romer is able to correct polarisation fraction outliers that are found when using the dirty Faraday spectra. In this work, I also developed two additional frameworks to calibrate cross-hand polarisation for eMERLIN observations towards Abell 1314, demonstrating the importance of such self-calibration by showing an improvement in signal-to-noise from 91.7 to 524.7.

Date of Award	31 Dec 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Paddy Leahy (Supervisor) & Anna Scaife (Supervisor)