Exploring the Magnetic Fields of the Milky Way and Magellanic System
Creators: name: Livingston, Jack
Publisher: name: The Australian National University
Year: 2022

description: There is a vitally important yet understudied aspect of astrophysics, one that works on large and small scales, regulating star-formation, tracing galaxy mergers and interactions, permeating the entire Universe: astrophysical magnetic fields. Radio polarimetry, is a powerful tool that enables us to explore these astrophysics magnetic fields. Soon, the next generation of telescopes like the Australian Square Kilometre Array (SKA) Pathfinder (ASKAP) will be fully functional for radio polarimetry observations, and projects like the Polarised Sky Survey of the Universe's Magnetism (POSSUM) will require test targets before they undertake all-sky surveys. This thesis acts as a bridge between early radio polarisation studies and the next steps in the study of astrophysical magnetic fields, heading towards the epoch of ASKAP and the SKA. In this thesis, we investigate the magnetic fields of the Magellanic Clouds and Milky Way (MW) using both archival and specifically acquired polarisation data from the Australia Telescope Compact Array (ATCA). In total this thesis adds 327 new polarised sight-lines across the MW and Magellanic Clouds, creates a novel characterisation of magnetic field complexity, and marks the most detailed analysis of the line-of-sight magnetic fields of the Magellanic Clouds to date. This work spans magnetic field size scales from parsec size to the size of an interacting galaxy system. Firstly, we produce a study of Faraday complexity of the inner one kiloparsec of the Galactic Centre (GC), finding that the GC is significantly more complex than the rest of the magnetised sky. By using a variety of different models for the magneto-ionic environment along the line-of-sight we find a magnetic field that is highly spatially variable, indicating the presence of small-scale magneto-ionic turbulence. The source of this turbulence likely comes from stellar feedback and enhanced star formation within the GC. Broadening our perspective, we observe the magnetic fields of the Small Magellanic Cloud (SMC) to investigate how magnetic fields manifest on galactic scales in low-mass galaxies. In the process of our study, we increase the number of measurements of the magnetic fields of the SMC by an order of magnitude. The large-scale magnetic field of the SMC is generally directed away from us, with a prominent random magnetic field component. We find evidence of the SMC magnetising its immediate surroundings and of magnetised cold gas outflows coming from north of the main body of the SMC. We also observe a similarity between the magnetic fields of the SMC and the Magellanic Bridge (MB), indicating a possible connection between the two in a `pan-Magellanic' magnetic field. Continuing this work on the Magellanic System, we study the magnetic fields of the Large Magellanic Cloud (LMC) and their connection to the Magellanic System. Our work doubles the available measurements of the line-of-sight magnetic fields of the LMC. Combining this data with previous observations of the LMC, we find that the large-scale magnetic field of the LMC deviates from the previously proposed spiral-like magnetic field. Like the SMC the magnetic field of the LMC has a prominent random component and its surroundings are magnetised. However, the LMC does not share the same field orientation as the SMC and the MB indicating it likely has a field not directly connected with the `pan-Magellanic' magnetic field. The Magellanic Clouds and the GC are two areas of the magnetised sky that warrant further investigation due to their implications on the nature of astrophysical magnetic fields and their proximity. Projects like POSSUM and future projects with the SKA can conduct follow up observations of the GC and the Magellanic Clouds to continue to explore small-scale magneto-ionic turbulence, the magnetic fields of low-mass galaxies, and how interacting galaxy systems affect and are affected by their magnetic fields.