Purpose of the Program

Use HAWC+ to measure far infrared polarization toward the largest filaments in the Milky Way.

Principal Investigator

Ian Stephens (Worcester State University and Harvard/CfA)

Proposal ID and Data Access


Proposal Abstract

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.


I. W. Stephens, P. C. Myers, C. Zucker, J. M. Jackson, B.-G. Andersson, R. Smith, A. Soam, C. Battersby, P. Sanhueza, T. Hogge, H. A. Smith, G. Novak, S. Sadavoy, T. G. S. Pillai, Z.-Y. Li, L. W. Looney, K. Sugitani, S. Coudé, A. Guzmán, A. Goodman, T. Kusune, F. P. Santos, L. Zuckerman, and F. Encalada, The Magnetic Field in the Milky Way Filamentary Bone G47. The Astrophysical Journal 926, L6 (2022).

External website of the PI team