Magnetic fields around Radio Galaxies

Student thesis: Phd


Magnetic fields are ubiquitous throughout the universe, but are still relatively poorly understood. POSSUM, the Polarisation Sky Survey of the Universe's Magnetism, will use ASKAP, the Australian Square Kilometre Array Pathfinder, to perform a full continuum radio polarisation survey of the southern sky. When linearly polarised radio emission passes through a magneto-ionised medium it experiences a rotation of its polarisation angle, known as Faraday Rotation. This effect is frequency dependent, and a broadband polarimetry analysis allows for the reconstruction of any magnetic fields along the line of sight. This thesis aims to use preliminary POSSUM data to gain insights into the magnetic fields around radio galaxies. A focus is made on the efficient processing of the data products (the most relevant being images) produced by the ASKAP observatory. Data from POSSUM Early Science and Pilot observations have been used to construct a user-friendly pipeline which is able to tackle the increasingly large quantities of data that ASKAP produces. This pipeline has been used to analyse 42 galaxies and galaxy groups from a POSSUM Early Science field and the POSSUM Pilot I survey. For the Pilot survey, the sample is complete down to an object size of 2 square arcminutes to a sensitivity of ~30 micro Jy/bm. This has involved mapping of various polarisation properties across numerous radio galaxy lobes including polarisation fraction, polarisation intensity, Faraday rotation, and depolarisation. This work represents a significant increase in the number of well-resolved radio galaxies studied to this level of detail, with the majority of the sources being mapped in this way for the first time. Extensive cross-matching has also been undertaken between the ASKAP radio observations and other wavelengths, result- ing in new host identifications in some cases, and leading to the independent discovery of 7 new Giant Radio Galaxies (GRGs). Statistical analyses have also been performed on the data, comparing the statistics and structures within sources in addition to the sample as a whole. In conclusion, this work represents a significant increase in the number of well-resolved radio galaxy lobes with detailed polarisation mapping. The polarisation properties derived have been used to consider the local magnetoionic environments of the radio lobes, and number of new cross-identifications have been made. The work has been undertaken in a way which sets up efficient processing pipelines for the continuing and future influx of data from ASKAP, paving the way for SKA-era levels of data processing.
Date of Award31 Dec 2022
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorPaddy Leahy (Supervisor) & Anna Scaife (Supervisor)


  • Faraday Rotation
  • Radio Astronomy
  • Polarimetry
  • Magnetic Fields
  • Radio Galaxies

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