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POSSUM: Polarisation Sky Survey

of the Universe's Magnetism

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The Australian Square Kilometre Array Pathfinder (ASKAP) is a next-generation radio telescope about to commence operations in outback Australia. ASKAP's large instantaneous field-of-view allows it to survey the sky vastly faster than is possible with existing radio telescopes, allowing us to address fundamental questions about the origin and evolution of the Universe.

The "Polarisation Sky Survey of the Universe's Magnetism" (POSSUM) is one of the eight major surveys to be undertaken on ASKAP. POSSUM will be a continuum polarisation survey of the entire sky south of +30 degrees, covering the frequency range 1130-1430 MHz to an RMS sensitivity of 10 μJy/beam at 10-arcsec resolution. The main result will be a catalogue of Faraday rotation measures (RMs) for around a million extragalactic radio sources at a density of approximately 25 RMs per deg^2. This data set will allow us to determine the 3D geometry of the Milky Way's magnetic field, to test dynamo and other models for magnetic field generation, and to carry out a comprehensive census of magnetic fields as a function of redshift in galaxies, in clusters and in the overall intergalactic medium.