GTC/CanariCam Mid-infrared Polarimetry of Magnetic Fields in Star-forming Region W51 IRS2

Abstract

We present 0.″4 resolution imaging polarimetry at 8.7, 10.3, and 12.5 μm, obtained with CanariCam at the Gran Telescopio Canarias, of the central 0.11 pc × 0.28 pc (4.″2 × 10.″8) region of W51 IRS2. The polarization, as high as ∼14%, arises from silicate particles aligned by the interstellar magnetic field (B-field). We separate, or unfold, the polarization of each sightline 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-infrared (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 B-field across the W51 IRS2W cometary core appears to be an integral part of a champagne outflow of gas originating in the core and dominating the energetics there. The bipolar outflow, W51north jet, that appears to originate at or near SMA1/N1 coincides almost exactly with a clearly demarcated north–south swath of lower polarization. While speculative, comparison of mid-IR and submillimeter polarimetry on two different scales may support a picture in which SMA1/N1 plays a major role in the B-field structure across W51 IRS2.