The JCMT BISTRO Survey: multiwavelength polarimetry of bright regions in NGC 2071 in the far-infrared/submillimetre range, with POL-2 and HAWC+
Fanciullo, Lapo; Kemper, Francisca; Pattle, Kate; Koch, Patrick M; Sadavoy, Sarah; Coude, Simon; Archana Soam; Hoang, Thiem; Onaka, Takashi; Gouellec, Valentin J M Le; Arzoumanian, Doris; Berry, David; Eswaraiah, Chakali; Chung, Eun Jung; Furuya, Ray; Hull, Charles L H; Hwang, Jihye; Johnstone, Douglas; Kang, Ji-hyun; Kim, Kyoung Hee; Kirchschlager, Florian; Konyves, Vera; Kwon, Jungmi; Kwon, Woojin; Lai, Shih-Ping; Lee, Chang Won; Liu, Tie; Lyo, A-Ran; Stephens, Ian; Tamura, Motohide; Tang, Xindi; Ward-Thompson, Derek; Whitworth, Anthony; Shinnaga, Hiroko
Date:
2022-05
Abstract:
Polarized dust emission is a key tracer in the study of interstellar medium and of star formation. The observed polarization,
however, is a product of magnetic field structure, dust grain properties, and grain alignment efficiency, as well as their variations
in the line of sight, making it difficult to interpret polarization unambiguously. The comparison of polarimetry at multiple
wavelengths is a possible way of mitigating this problem. We use data from HAWC+ /SOFIA and from SCUBA-2/POL-2
(from the BISTRO survey) to analyse the NGC 2071 molecular cloud at 154, 214, and 850 μm. The polarization angle changes
significantly with wavelength over part of NGC 2071, suggesting a change in magnetic field morphology on the line of sight
as each wavelength best traces different dust populations. Other possible explanations are the existence of more than one
polarization mechanism in the cloud or scattering from very large grains. The observed change of polarization fraction with
wavelength, and the 214-to-154 μm polarization ratio in particular, are difficult to reproduce with current dust models under
the assumption of uniform alignment efficiency. We also show that the standard procedure of using monochromatic intensity
as a proxy for column density may produce spurious results at HAWC+wavelengths. Using both long-wavelength (POL-2,
850 μm) and short-wavelength (HAWC+, 200 μm) polarimetry is key in obtaining these results. This study clearly shows the
importance of multi-wavelength polarimetry at submillimetre bands to understand the dust properties of molecular clouds and
the relationship between magnetic field and star formation.
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