Abstract
Dust polarization observations are a powerful, practical tool to probe the geometry (and to some extent, the strength) of magnetic fields in starforming regions. In particular, Planck polarization data have revealed the importance of magnetic fields on large scales in molecular clouds. However, due to insufficient resolution, Planck observations are unable to constrain the B-field geometry on prestellar and protostellar scales. The high angular resolution of 11.7 arcsec provided by NIKA2-Pol 1.15 mm polarimetric imaging, corresponding to 0.02 pc at the distance of the Orion molecular cloud (OMC), makes it possible to advance our understanding of the B-field morphology in star-forming filaments and dense cores (IRAM 30m large program B-FUN). The commissioning of the NIKA2-Pol instrument has led to several challenging issues, in particular, the instrumental polarization or intensity-to-polarization “leakage” effect. In the present paper, we illustrate how this effect can be corrected for, leading to reliable exploitable data in a structured, extended source such as OMC-1. We present a statistical comparison between NIKA2-Pol and SCUBA2-Pol2 results in the OMC-1 region. We also present tentative evidence of local pinching of the B-field lines near Orion-KL, in the form of a new small-scale hourglass pattern, in addition to the larger-scale hourglass already seen by other instruments such as Pol2.
Highlights
Observations of nearby molecular clouds by the Herschel Gould Belt Survey have shown the crucial role of filaments in the star formation process [3, 4], but the detailed fragmentation manner of star-forming filaments remains under debate
The IRAM 30m large program B-FUN will perform high-resolution polarization observations of a broad sample of nearby star-forming filaments imaged by Herschel [3], in an effort to improve our understanding of the role of magnetic fields in core/star formation along filaments
It is important to characterize the B-field at different wavelengths and high angular resolution to understand how it is involved in the star formation process [5, 9, 14]
Summary
Observations of nearby molecular clouds by the Herschel Gould Belt Survey have shown the crucial role of filaments in the star formation process [3, 4], but the detailed fragmentation manner of star-forming filaments remains under debate. Stars form inside molecular filaments characterized by a common inner width of ∼0.1 pc [7] and the angular resolution of Planck is insufficient to probe the geometry of the B-field in the
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