"The Thing": Investigating a massive depolarisation region in radio frequency maps of the Milky Way

Magnetic fields structurally support the Galactic disk, modulate the star formation rate, and store a non-negligible amount of the Milky Way's total energy budget. Although we have some idea of how gas, dust, stars, and planets are distributed throughout the Galaxy, how they came to be remains a mystery. Mapping the three-dimensional structure of Galactic magnetic fields is a key piece in the puzzle of Galaxy formation and evolution. Unfortunately for us, magnetic fields do not emit light, and as a result, they cannot be mapped directly. Luckily, nature gifted us with an indirect means of measuring the magnetic field of the Galaxy. Galactic regions containing ionised matter and magnetic fields alter the polarisation properties of light before it arrives on Earth. I am part of the Global Magneto-Ionic Medium Survey (GMIMS) collaboration, which aims to map the polarisation properties of the Milky Way's radio emissions using radio telescopes. A remarkable observation that came out of GMIMS is "The Thing". "The Thing" is a massive portion of the polarised sky that vanishes at low enough radio frequencies (~500 MHz). In my talk, I will discuss different physical mechanisms that may produce "The Thing" and explain how we use it to probe the three-dimensional magnetic field structure of the Galaxy.