GTC/CanariCam Mid-IR Polarimetry of Magnetic Fields in Star-Forming Region W51 IRS2

Swanson, Pae; Telesco, Charles; Zhang, Han; Varosi, Frank; Fernandez-Acosta, Sergio; Wright, Christopher; Packham, Christopher
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American Astronomical Society Meeting Abstracts

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We present 0.4 arcsec-resolution mid-IR imaging polarimetry, obtained with CanariCam at GTC, of the central 0.11 pc x 0.28 pc (4.2 arcsec x 10.8 arcsec) region of W51 IRS2. The observed mid-IR polarization across this region is typically several percent, with values as high as 12%. The polarization arises from ensembles of non-spherical silicate particles aligned by the interstellar magnetic field (B-field). Applying Aitken's method, we decompose the polarization of each sight line into emission and absorption components, from which we infer the morphologies of the corresponding projected B-fields that thread the emitting and foreground-absorbing regions. We conclude that the projected B-field in the foreground material is part of the larger-scale ambient field. The morphology of the projected B-field in the mid-IR emitting region spanning the cometary H II region W51 IRS2W is similar to that in the absorbing region. Elsewhere, the two B-fields differ significantly with no clear relationship between them. The morphology of the B-field in W51 IRS2W implies that it may be an integral part of a champagne outflow of gas originating in the cometary core and merging with one or more of the previously observed large-scale outflows, in qualitative agreement with MHD simulations by Gendelev & Krumholz (2012). In those models, outflowing gas powered by an OB star is funneled along a preexisting ambient B-field while also perturbing that B-field locally. This research is supported by NSF grant AST-1908625 to C. Telesco.