FIELDMAPS: Filaments Extremely Long and Dark: A Magnetic Polarization Survey (Pilot Legacy Program)
PI: Ian Stephens (Harvard & Smithsonian Center for Astrophysics)
Selected in Cycle 8
Proposal ID: 08_0186
Instrument: HAWC+

Abstract Excerpt: Molecular gas in a galaxy generally follows the spiral arms. In the Milky Way, the densest of this molecular gas can form long, velocity-coherent filaments parallel and in close proximity to the Galactic plane. These dense filaments make up the 'skeleton' of molecular gas of the Milky Way - akin to the dark dust lanes seen in nearby spiral galaxies - and thus have been called 'bones.' For the early stages of star formation, these bones represent the largest star-forming structures in the Galaxy, and previous studies suggest that magnetic fields are critical to their formation. Our pilot survey of 2 bones show that HAWC+ can detect polarization over large angular extents with modest integration time. To understand how gas collects in the magnetized spiral potential, we propose a legacy survey to probe the magnetic fields across the entire extent of 8 additional bones (for a total of 10). We will use these observations in combination with new magnetohydrodynamical simulations of galactic formation of bones to investigate (1) the role of magnetic fields in the formation of bones, (2) how the field varies between arm and inter-arm bones, and (3) whether or not fields bend into filaments to build gas flows to the largest gravitational potential well.

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