Cataloguing Discrete Radio Sources and Widefield Imaging in Nearby Galaxies

Abstract

The study of nearby galaxies such as M82 is vital in developing an understanding of the structure and evolution of galaxies in the local Universe. Key to this is the cataloguing and monitoring of the discrete radio source populations within these galaxies. The radio emission from these nearby galaxies is dominated by star formation and accretion processes. Advancements in widefield imaging techniques have meant that the generation of images covering the extent of a galaxy (roughly 9 arcmin in the case of M82) is becoming more feasible. This maximises the region in which sources can be located and gives a much fuller understanding of the galaxy as a whole. Although becoming more feasible, accurately performing high resolution widefield imaging is still a very computationally expensive task which requires the use of high-performance computing resources. In this thesis the optimisation of this widefield source finding process is investigated, applied to 2019 shallow snapshot imaging mode LeMMINGs C-band observations of M82. The inability to generate full resolution (8 mas pixel) widefield images utilizing standard computing resources meant that a low resolution (40 mas pixel) widefield imaging approach was taken. Source finding with PYBDSF was applied to this low resolution widefield image. Previous literature with deeper observations meant that the results could be cross-referenced to determine the efficacy of the techniques and parameters applied. Due to the low sensitivity observations, only nine real sources were detected in these data, with eight in the central M82 region and one previously undetected (SMUDge) over 4 arcmin eastwards from the centre, on the outskirts of the galaxys extent. These sources consisted of seven SNRs, one SN and one unknown (possible HMXRB). Although the source finding was successful on the low resolution image, the scientific parameter extraction was less successful. Full resolution images were created through two methods: one WSCLEAN full resolution widefield image and TCLEAN cut-out images of individual sources. The WSCLEAN widefield image resulted in the most accurate parameters and image statistics, but the TCLEAN cut-outs gave reasonable results much more efficiently. Through a number of methods the supernova rate was determined to be 0.024-0.030 per year. The star-formation rate of stars >5 Solar masses was determined from these supernova rate values, through the Miller-Scalo IMF, to be 0.60-0.75 Solar masses per year. Both of these values are lower than those calculated in previous literature due to the incomplete nature of the observation caused by the lack of sensitivity and limited image fidelity.

Date of Award	1 Aug 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Neal Jackson (Supervisor) & Rob Beswick (Supervisor)