Planck intermediate results

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

¹ APC, AstroParticule et Cosmologie, Université Paris Diderot, CNRS/IN2P3, CEA/lrfu, Observatoire de Paris, Sorbonne Paris Cité, 10 rue Alice Domon et Léonie Duquet, 75205 Paris Cedex 13, France
² African Institute for Mathematical Sciences, 6–8 Melrose Road, Muizenberg, 7945 Cape Town, South Africa
³ Agenzia Spaziale Italiana Science Data Center, via del Politecnico snc, 00133 Roma, Italy
⁴ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
⁵ Astrophysics Group, Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, UK
⁶ Astrophysics & Cosmology Research Unit, School of Mathematics, Statistics & Computer Science, University of KwaZulu-Natal, Westville Campus, Private Bag X54001, Durban 4000, South Africa
⁷ CITA, University of Toronto, 60 St. George St., Toronto, ON M5S 3H8, Canada
⁸ CNRS, IRAP, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
⁹ California Institute of Technology, Pasadena, California, USA
¹⁰ Centro de Estudios de Física del Cosmos de Aragón (CEFCA), Plaza San Juan, 1, planta 2, 44001 Teruel, Spain
¹¹ Computational Cosmology Center, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 California, USA
¹² Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain
¹³ DSM/Irfu/SPP, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
¹⁴ DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, 2800 Kgs. Lyngby, Denmark
¹⁵ Département de Physique Théorique, Université de Genève, 24 Quai E.Ansermet, 1211 Genève 4, Switzerland
¹⁶ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206, La Laguna, Tenerife, Spain
¹⁷ Departamento de Física, Universidad de Oviedo, Avda. Calvo Sotelo s/n, 33003 Oviedo, Spain
¹⁸ Department of Astrophysics/IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands
¹⁹ Department of Physics & Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, British Columbia, Canada
²⁰ Department of Physics and Astronomy, Dana and David Dornsife College of Letter, Arts and Sciences, University of Southern California, Los Angeles, CA 90089, USA
²¹ Department of Physics and Astronomy, University College London, London WC1E 6BT, UK
²² Department of Physics, Florida State University, Keen Physics Building, 77 Chieftan Way, Tallahassee, Florida, USA
²³ Department of Physics, Gustaf Hällströmin katu 2a, University of Helsinki, 00100 Helsinki, Finland
²⁴ Department of Physics, Princeton University, Princeton, NJ 08544 New Jersey, USA
²⁵ Department of Physics, University of California, Santa Barbara, California, USA
²⁶ Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois, USA
²⁷ Dipartimento di Fisica e Astronomia G. Galilei, Università degli Studi di Padova, via Marzolo 8, 35131 Padova, Italy
²⁸ Dipartimento di Fisica e Scienze della Terra, Università di Ferrara, via Saragat 1, 44122 Ferrara, Italy
²⁹ Dipartimento di Fisica, Università La Sapienza, P.le A. Moro 2 Roma, Italy
³⁰ Dipartimento di Fisica, Università degli Studi di Milano, via Celoria, 16 Milano, Italy
³¹ Dipartimento di Fisica, Università degli Studi di Trieste, via A. Valerio 2, 34128 Trieste, Italy
³² Dipartimento di Fisica, Università di Roma Tor Vergata, via della Ricerca Scientifica, 1 Roma, Italy
³³ Dipartimento di Matematica, Università di Roma Tor Vergata, via della Ricerca Scientifica, 1 Roma, Italy
³⁴ Discovery Center, Niels Bohr Institute, Blegdamsvej 17, Copenhagen, Denmark
³⁵ European Space Agency, ESAC, Planck Science Office, Camino bajo del Castillo, s/n, Urbanización Villafranca del Castillo, Villanueva de la Cañada, 28692 Madrid, Spain
³⁶ European Space Agency, ESTEC, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
³⁷ Facoltà di Ingegneria, Università degli Studi e-Campus, via Isimbardi 10, 22060 Novedrate ( CO), Italy
³⁸ Gran Sasso Science Institute, INFN, viale F. Crispi 7, 67100 L’Aquila, Italy
³⁹ HGSFP and University of Heidelberg, Theoretical Physics Department, Philosophenweg 16, 69120 Heidelberg, Germany
⁴⁰ Helsinki Institute of Physics, Gustaf Hällströmin katu 2, University of Helsinki, Helsinki, Finland
⁴¹ INAF–Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, Padova, Italy
⁴² INAF–Osservatorio Astronomico di Roma, via di Frascati 33, Monte Porzio Catone, Italy
⁴³ INAF–Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, Trieste, Italy
⁴⁴ INAF/IASF Bologna, via Gobetti 101, Bologna, Italy
⁴⁵ INAF/IASF Milano, via E. Bassini 15, Milano, Italy
⁴⁶ INFN, Sezione di Bologna, via Irnerio 46, 40126 Bologna, Italy
⁴⁷ INFN, Sezione di Roma 1, Università di Roma Sapienza, Piazzale Aldo Moro 2, 00185 Roma, Italy
⁴⁸ INFN, Sezione di Roma 2, Università di Roma Tor Vergata, via della Ricerca Scientifica, 1 Roma, Italy
⁴⁹ INFN/National Institute for Nuclear Physics, via Valerio 2, 34127 Trieste, Italy
⁵⁰ IUCAA, Post Bag 4, Ganeshkhind, Pune University Campus, Pune 411 007, India
⁵¹ Imperial College London, Astrophysics group, Blackett Laboratory, Prince Consort Road, London, SW7 2AZ, UK
⁵² Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125, USA
⁵³ Institut d’Astrophysique Spatiale, CNRS (UMR 8617) Université Paris-Sud 11, Bâtiment 121, Orsay, France
⁵⁴ Institut d’Astrophysique de Paris, CNRS (UMR 7095), 98bis Boulevard Arago, 75014 Paris, France
⁵⁵ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁵⁶ Institute of Theoretical Astrophysics, University of Oslo, Blindern, Oslo, Norway
⁵⁷ Instituto de Astrofísica de Canarias, C/Vía Láctea s/n, La Laguna, 38205 Tenerife, Spain
⁵⁸ Instituto de Física de Cantabria (CSIC-Universidad de Cantabria), Avda. de los Castros s/n, Santander, Spain
⁵⁹ IstitutoNazionale di Fisica Nucleare, Sezione di Padova, via Marzolo 8, 35131 Padova, Italy
⁶⁰ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California, USA
⁶¹ Jodrell Bank Centre for Astrophysics, Alan Turing Building, School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK
⁶² Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637, USA
⁶³ Kavli Institute for Cosmology Cambridge, Madingley Road, Cambridge, CB3 0HA, UK
⁶⁴ Kazan Federal University, 18 Kremlyovskaya St., 420008 Kazan, Russia
⁶⁵ LAL, Université Paris-Sud, CNRS/IN2P3, 91400 Orsay, France
⁶⁶ LERMA, CNRS, Observatoire de Paris, 61 Avenue de l’Observatoire, 75014 Paris, France
⁶⁷ Laboratoire AIM, IRFU/Service d’Astrophysique – CEA/DSM – CNRS – Université Paris Diderot, Bât. 709, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
⁶⁸ Laboratoire Traitement et Communication de l’Information, CNRS (UMR 5141) and Télécom ParisTech, 46 rue Barrault 75634 Paris Cedex 13, France
⁶⁹ Laboratoire de Physique Subatomique et Cosmologie, Université Grenoble-Alpes, CNRS/IN2P3, 53, rue des Martyrs, 38026 Grenoble Cedex, France
⁷⁰ Laboratoire de Physique Théorique, Université Paris-Sud 11 and CNRS, Bâtiment 210, 91405 Orsay, France
⁷¹ Lawrence Berkeley National Laboratory, Berkeley, CA 94720 California, USA
⁷² Lebedev Physical Institute of the Russian Academy of Sciences, Astro Space Centre, 84/32 Profsoyuznaya st., 117997 Moscow, GSP-7, Russia
⁷³ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany
⁷⁴ McGill Physics, Ernest Rutherford Physics Building, McGill University, 3600 rue University, Montréal, QC, H3A 2T8, Canada
⁷⁵ National University of Ireland, Department of Experimental Physics, Maynooth, Co. Kildare, Ireland
⁷⁶ Nicolaus Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw, Poland
⁷⁷ Niels Bohr Institute, Blegdamsvej 17, 2100 Copenhagen, Denmark
⁷⁸ Optical Science Laboratory, University College London, Gower Street, WC1E 6 BT London, UK
⁷⁹ SISSA, Astrophysics Sector, via Bonomea 265, 34136 Trieste, Italy
⁸⁰ School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff, CF24 3AA, UK
⁸¹ Sorbonne Université-UPMC, UMR 7095, Institut d’Astrophysique de Paris, 98bis Boulevard Arago, 75014 Paris, France
⁸² Space Sciences Laboratory, University of California, Berkeley, California, USA
⁸³ Special Astrophysical Observatory, Russian Academy of Sciences, Nizhnij Arkhyz, Zelenchukskiy region, 369167 Karachai-Cherkessian Republic, Russia
⁸⁴ Sub-Department of Astrophysics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
⁸⁵ UPMC Univ Paris 06, UMR 7095, 98bis Boulevard Arago, 75014 Paris, France
⁸⁶ Université de Toulouse, UPS-OMP, IRAP, 31028 Toulouse Cedex 4, France
⁸⁷ University of Granada, Departamento de Física Teórica y del Cosmos, Facultad de Ciencias, 18071 Granada, Spain
⁸⁸ University of Granada, Instituto Carlos I de Física Teórica y Computacional, 18071 Granada, Spain
⁸⁹ Warsaw University Observatory, Aleje Ujazdowskie 4, 00-478 Warszawa, Poland

Received: 9 November 2014
Accepted: 12 September 2015

Abstract

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 (N_H 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 (ψ_fil) are coherent along their lengths and not the same as in their backgrounds (ψ_bg). The differences between ψ_fil and ψ_bg 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 N_H 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 (σ_ψ< 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.