Bibcode
Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Alves, M. I. R.; Arnaud, M.; Arzoumanian, D.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartolo, N.; Battaner, E.; Benabed, K.; Benoit-Lévy, A.; Bernard, J.-P.; Berné, O.; Bersanelli, M.; Bielewicz, P.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bracco, A.; Burigana, C.; Calabrese, E.; Cardoso, J.-F.; Catalano, A.; Chamballu, A.; Chiang, H. C.; Christensen, P. R.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Combet, C.; Couchot, F.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Dickinson, C.; Diego, J. M.; Donzelli, S.; Doré, O.; Douspis, M.; Ducout, A.; Dupac, X.; Elsner, F.; Enßlin, T. A.; Eriksen, H. K.; Falgarone, E.; Ferrière, K.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Frejsel, A.; Galeotta, S.; Galli, S.; Ganga, K.; Ghosh, T.; Giard, M.; Giraud-Héraud, Y.; Gjerløw, E.; González-Nuevo, J.; Górski, K. M.; Gregorio, A.; Gruppuso, A.; Guillet, V.; Hansen, F. K.; Hanson, D.; Harrison, D. L.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Juvela, M.; Keskitalo, R.; Kisner, T. S.; Knoche, J.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lamarre, J.-M.; Lasenby, A. et al.
Bibliographical reference
Astronomy and Astrophysics, Volume 586, id.A136, 16 pp.
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2
2016
Journal
Citations
88
Refereed citations
80
Description
Planck observations at 353 GHz provide the first fully sampled maps of
the polarized dust emission towards interstellar filaments and their
backgrounds (i.e., the emission observed in the surroundings of the
filaments). The data allow us to determine the intrinsic polarization
properties of the filaments and therefore to provide insight into the
structure of their magnetic field (B). We present the polarization maps
of three nearby (several parsecs long) star-forming filaments of
moderate column density (NH about 1022
cm-2): Musca, B211, and L1506. These three filaments are
detected above the background in dust total and polarized emission. We
use the spatial information to separate Stokes I, Q, and U of the
filaments from those of their backgrounds, an essential step in
measuring the intrinsic polarization fraction (p) and angle (ψ) of
each emission component. We find that the polarization angles in the
three filaments (ψfil) are coherent along their lengths
and not the same as in their backgrounds (ψbg). The
differences between ψfil and ψbg are
12° and 54° for Musca and L1506, respectively, and only 6°
in the case of B211. These differences forMusca and L1506 are larger
than the dispersions of ψ, both along the filaments and in their
backgrounds. The observed changes of ψ are direct evidence of
variations of the orientation of the plane of the sky (POS) projection
of the magnetic field. As in previous studies, we find a decrease of
several per cent in p with NH from the backgrounds to the
crest of the filaments. We show that the bulk of the drop in p within
the filaments cannot be explained by random fluctuations of the
orientation of the magnetic field because they are too small
(σψ< 10°). We recognize the degeneracy
between the dust alignment efficiency (by, e.g., radiative torques) and
the structure of the B-field in causing variations in p, but we argue
that the decrease in p from the backgrounds to the filaments results in
part from depolarization associated with the 3D structure of the
B-field: both its orientation in the POS and with respect to the POS. We
do not resolve the inner structure of the filaments, but at the smallest
scales accessible with Planck (~0.2 pc), the observed changes of ψ
and p hold information on the magnetic field structure within filaments.
They show that both the mean field and its fluctuations in the filaments
are different from those of their backgrounds, which points to a
coupling between the matter and the B-field in the filament formation
process.