Revealing cosmic magnetism with the Square Kilometre Array and its pathfinders

Magnetism is an enigmatic but crucial element of our Universe. The structure and strength of magnetic fields are important for a full understanding of astrophysics over a tremendous range of scales: from stellar systems, to star forming regions, the properties and evolution of individual galaxies, galaxy groups and clusters, and even as a major element of the Cosmic Web. The Square Kilometre Array (SKA) promises to deliver a revolutionary view of the magnetised Universe, through the delivery of a dense all-sky grid of Faraday rotation measures (RMs) with SKA1-MID, and exquisite sensitivity to weak magnetic fields and tenuous ionized gas reservoirs with SKA1-LOW. In this talk, I will describe some of the key innovations and results that are emerging from pathfinder polarization surveys with SKA pathfinders and precursors including the Australian SKA Pathfinder (ASKAP), the Murchison Widefield Array (MWA), and the Low Frequency Array (LOFAR). In particular, I will highlight the value of polarization surveys as a novel discovery pathway for pulsars and stellar systems; explain how our first SKA-like RM Grids are crucial for uncovering extended distributions of ionised gas; and present ongoing work to constrain the detailed internal structure and evolution of magnetic fields in galaxies through the strong frequency dependence of the polarized sky. I will conclude by describing the plans that are being developed to use the SKA itself to generate a three-dimensional map of the magnetic field across the Universe.