Polarization Properties and Magnetic Field Structures in the High-mass Star-forming Region W51 Observed with ALMA

We present the first ALMA dust polarization observations toward the high-mass star-forming regions W51 e2, e8, and W51 North in Band 6 (230 GHz) with a resolution of about (∼5 mpc). Polarized emission in all three sources is clearly detected and resolved. Measured relative polarization levels are be...

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Bibliographic Details
Published in:The Astrophysical journal 2018-03, Vol.855 (1), p.39
Main Authors: Koch, Patrick M., Tang, Ya-Wen, Ho, Paul T. P., Yen, Hsi-Wei, Su, Yu-Nung, Takakuwa, Shigehisa
Format: Article
Language:English
Subjects:
Astrophysics
Convergence
Convergence zones
Cosmic dust
Gravitation
ISM: individual objects: (W51 e2, W51 e8, W51 North)
ISM: magnetic fields
Magnetic fields
Magnetic properties
Massive stars
Morphology
Polarization
Star formation
Stars & galaxies
stars: formation
Substructures
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Summary:We present the first ALMA dust polarization observations toward the high-mass star-forming regions W51 e2, e8, and W51 North in Band 6 (230 GHz) with a resolution of about (∼5 mpc). Polarized emission in all three sources is clearly detected and resolved. Measured relative polarization levels are between 0.1% and 10%. While the absolute polarization shows complicated structures, the relative polarization displays the typical anticorrelation with Stokes I, although with a large scatter. Inferred magnetic (B) field morphologies are organized and connected. Detailed substructures are resolved, revealing new features such as comet-shaped B-field morphologies in satellite cores, symmetrically converging B-field zones, and possibly streamlined morphologies. The local B-field dispersion shows some anticorrelation with the relative polarization. Moreover, the lowest polarization percentages together with largest dispersions coincide with B-field convergence zones. We put forward , where is the measurable angle between a local B-field orientation and local gravity, as a measure of how effectively the B field can oppose gravity. Maps of for all three sources show organized structures that suggest a locally varying role of the B field, with some regions where gravity can largely act unaffectedly, possibly in a network of narrow magnetic channels, and other regions where the B field can work maximally against gravity.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/aaa4c1