2025/09/30 by Coudé, Simon, Stephens, Ian W., Myers, Philip C. +13 · 1 citation
#Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences
paper · doi:10.48550/arxiv.2509.25832
Polarization observations of the Milky Way and many other spiral galaxies have found a close correspondence between the orientation of spiral arms and magnetic field lines on scales of hundreds of parsecs. This paper presents polarization measurements at 214 μm toward ten filamentary candidate ``bones" in the Milky Way using the High-resolution Airborne Wide-band Camera (HAWC+) on the Stratospheric Observatory for Infrared Astronomy (SOFIA). These data were taken as part of the Filaments Extremely Long and Dark: A Magnetic Polarization Survey (FIELDMAPS) and represent the first study to resolve the magnetic field in spiral arms at parsec scales. We describe the complex yet well-defined polarization structure of all ten candidate bones, and we find a mean difference and standard deviation of -74∘ ± 32∘ between their filament axis and the plane-of-sky magnetic field, closer to a field perpendicular to their length rather than parallel. By contrast, the 850 μm polarization data from Planck on scales greater than 10 pc show a nearly parallel mean difference of 3∘ ± 21∘. These findings provide further evidence that magnetic fields can change orientation at the scale of dense molecular clouds, even along spiral arms. Finally, we use a power law to fit the dust polarization fraction as a function of total intensity on a cloud-by-cloud basis and find indices between -0.6 and -0.9, with a mean and standard deviation of -0.7 ± 0.1. The polarization, dust temperature, and column density data presented in this work are publicly available online.