Far-infrared Polarization Properties of Nearby Star-forming Regions: A New Compendium of SOFIA/HAWC+ Observations

TL;DR

This study provides a comprehensive analysis of far-infrared dust polarization in 26 nearby molecular clouds, revealing how polarization spectra depend on resolution, column density, and dust temperature, and highlighting the complex magnetic field structures in star-forming regions.

Contribution

It offers a new compendium of SOFIA/HAWC+ polarization data across multiple wavelengths and resolutions, analyzing scale-dependent magnetic field properties in nearby star-forming regions.

Findings

Polarization spectra depend more on column density than dust temperature.

Resolution influences the shape of the polarization spectrum, with 'falling' at small scales and 'flat' at larger scales.

Magnetic fields are decoupled from the large-scale Galactic plane in these regions.

Abstract

We present a comprehensive polarimetric study of 26 nearby molecular clouds in four far-infrared bands (53 $\mu$m to 214 $\mu$m) using 52 archival SOFIA/HAWC+ datasets. Far-infrared dust polarization observations probe the plane-of-sky magnetic field. To investigate scale-dependent trends, we group the molecular clouds by distance and analyze the data at common angular ($25''$) and common physical (0.052 pc and 0.32 pc) resolutions. The two shorter wavelengths are more impacted by smoothing, exhibiting a larger decrease in percent polarization. We analyze the polarization spectrum -- the polarization fraction as a function of wavelength -- and find that it depends more strongly on column density than dust temperature. We find a "falling" spectrum at the 0.052 pc resolution, but find a "flat" spectrum at the 0.32 pc resolution, suggesting that resolution plays an important role in the observed polarization spectra. We propose that warm dust grain emission in small-scale structures ($\lesssim$ 0.1 pc) traces different magnetic field geometries only resolved in our close regime data. There is no preferred magnetic field orientation across our data, which suggests that the magnetic field in our $\sim$ parsec scale regions is decoupled from the large-scale field that is primarily parallel to the Galactic plane. The relationship between percent polarization and column density varies between clouds, but the correlation between percent polarization and angular dispersion is consistent across regions. This compendium of dust polarization maps highlights the value of observing at multiple far-infrared wavelengths and will enable additional population-level studies of magnetic fields and dust across star-forming environments.