Mosaic polarisation calibration in large interferometric datasets

Abstract

In this thesis, I searched for polarised sources in the ATCA 2.1 GHz observations of the XXL-S field, observed in two parts - the pilot 6.5 deg² and the follow-up 20 deg², using the usual source finding with PyBDSF and the rotation measure synthesis technique. The source finding technique detected 39 polarised sources from a subset of the pilot data, with minimum and maximum total polarisation fractions of 2% and 30% respectively. Also, 150 polarised sources were detected in the follow-up survey with minimum and maximum total polarisation fractions of 0.6% and 53% respectively. The rotation measure synthesis detected 49 polarised sources from sources fitted with more than one Gaussian with PyBDSF. These analyses provide clear evidence of the efficiency of rotation measure synthesis for polarisation studies. We present catalogues of the polarised sources from both schemes and discuss extensively the parameters in each catalogue.

The polarised sources detected via source finding were then used to study the total intensity-polarised source counts to provide a significant contribution towards the polarised source controversy. Using nearly half the total number of sources detected in total intensity in both fields, the minimum polarised flux density detected is ∼0.28 mJy. Also, only fewer sources out of the detected total are polarised consistent with Rudnick & Owen (2014a,b). Using the polarised flux and their total intensity flux densities, I present a simple image-based direction-dependent leakage correction using a Maximum Likelihood technique to quantify the variation in leakages across the XXL-S mosaic.

I finally discuss ongoing efforts to improve the results discussed in this thesis and then propose a few potential areas of research feasible with the XXL-S datasets.

Date of Award	5 Dec 2023
Original language	English
Awarding Institution	University of Bristol
Supervisor	Mark Birkinshaw (Supervisor) & Malcolm N Bremer (Supervisor)