Planck intermediate results. XXXIII. Signature of the magnetic field geometry of interstellar filaments in dust polarization maps

Abstract : Planck observations at 353GHz provide the first fully-sampled maps of the polarized dust emission of interstellar filaments, offering unprecedented information on the structure of the magnetic field. We present the polarization properties of three nearby filaments, Musca, B211, and L1506. These three filaments have similar total intensities (Stokes I), while the variations of the Stokes Q and U are all different: the Musca filament is visible in the Q and U maps, B211 and L1506 are seen in the Q map but are not distinguishable in the U map, and the Q increase for L1506 is not spatially coincident with that of I. They all offer 3pc segments, along which both the filament and the background Stokes parameters are almost uniform. In all three cases, the polarization fraction (p) towards the filaments is smaller than that of their background. The polarized emission results from the combination of the magnetic field (B) structure and the dust polarization properties. We model the variations of the Stokes parameters across the filaments using variations solely of the orientation of B, assuming constant dust polarization fraction (p_0). Our modelling shows that the magnetic fields in the filaments and their background have an ordered component. We find that for L1506, the depolarization arises only from the rotation by 65^\circ of the plane of the sky (POS) projection of the field in the filament with respect to that of its background. For Musca and B211, the drop in p is due mostly to different orientations of B with respect to the POS inside and outside the filaments. The magnetic fields inside Musca and B211 are nearly orthogonal to their long axes, but almost parallel in the case of L1506. In spite of the degeneracy between p_0 and the angle of B with respect to the POS, we find that for Musca and B211 the quality of the fit is better for p_0 values larger than 13% and 7%, respectively.
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Astronomy and Astrophysics - A&A, EDP Sciences, 2016, 586, pp.A136. 〈10.1051/0004-6361/201425305〉
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Soumis le : vendredi 12 décembre 2014 - 16:14:02
Dernière modification le : lundi 9 avril 2018 - 12:22:07

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P.A.R. Ade, F. Couchot, Stéphane Plaszczynski, M. Tristram, A. Catalano, et al.. Planck intermediate results. XXXIII. Signature of the magnetic field geometry of interstellar filaments in dust polarization maps. Astronomy and Astrophysics - A&A, EDP Sciences, 2016, 586, pp.A136. 〈10.1051/0004-6361/201425305〉. 〈in2p3-01094627〉

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