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Aghanim, N. and Alves, M.I.R. and Arzoumanian, D. and Aumont, J. and Baccigalupi, C. and Ballardini, M. and Banday, A.J. and Barreiro, R.B. and Bartolo, N. and Basak, S. and Benabed, K. and Bernard, J.-P. and Bersanelli, M. and Bielewicz, P. and Bonavera, L. and Bond, J.R. and Borrill, J. and Bouchet, F.R. and Boulanger, F. and Bracco, A. and Bucher, M. and Burigana, C. and Calabrese, E. and Cardoso, J.-F. and Chiang, H.C. and Colombo, L.P.L. and Combet, C. and Comis, B. and Couchot, F. and Coulais, A. and Crill, B.P. and Curto, A. and Cuttaia, F. and Davis, R.J. and de Bernardis, P. and de Rosa, A. and de Zotti, G. and Delabrouille, J. and Delouis, J.-M. and Di Valentino, E. and Dickinson, C. and Diego, J.M. and Doré, O. and Douspis, M. and Ducout, A. and Dupac, X. and Dusini, S. and Efstathiou, G. and Elsner, F. and Enßlin, T.A. and Eriksen, H.K. and Falgarone, E. and Fantaye, Y. and Ferrière, K. and Finelli, F. and Frailis, M. and Fraisse, A.A. and Franceschi, E. and Frolov, A. and Galeotta, S. and Galli, S. and Ganga, K. and Génova-Santos, R.T. and Gerbino, M. and Ghosh, T. and González-Nuevo, J. and Górski, K.M. and Gratton, S. and Gregorio, A. and Gruppuso, A. and Gudmundsson, J.E. and Guillet, V. and Hansen, F.K. and Helou, G. and Henrot-Versillé, S. and Herranz, D. and Hivon, E. and Huang, Z. and Jaffe, A.H. and Jaffe, T.R. and Jones, W.C. and Keihänen, E. and Keskitalo, R. and Kisner, T.S. and Krachmalnicoff, N. and Kunz, M. and Kurki-Suonio, H. and Lagache, G. and Lähteenmäki, A. and Lamarre, J.-M. and Langer, M. and Lasenby, A. and Lattanzi, M. and Le Jeune, M. and Levrier, F. and Liguori, M. and Lilje, P.B. and López-Caniego, M. and Lubin, P.M. and Macías-Pérez, J.F. and Maggio, G. and Maino, D. and Mandolesi, N. and Mangilli, A. and Maris, M. and Martin, P.G. and Martínez-González, E. and Matarrese, S. and Mauri, N. and McEwen, J.D. and Melchiorri, A. and Mennella, A. and Migliaccio, M. and Miville-Deschênes, M.-A. and Molinari, D. and Moneti, A. and Montier, L. and Morgante, G. and Moss, Adam and Naselsky, P. and Natoli, P. and Neveu, J. and Nørgaard-Nielsen, H.U. and Oppermann, N. and Oxborrow, C.A. and Pagano, L. and Paoletti, D. and Partridge, B. and Perdereau, O. and Perotto, L. and Pettorino, V. and Piacentini, F. and Plaszczynski, S. and Polenta, G. and Rachen, J.P. and Rebolo, R. and Reinecke, M. and Remazeilles, M. and Renzi, A. and Ristorcelli, I. and Rocha, G. and Rossetti, M. and Roudier, G. and Ruiz-Granados, B. and Salvati, L. and Sandri, M. and Savelainen, M. and Scott, D. and Sirignano, C. and Soler, J.D. and Suur-Uski, A.-S. and Tauber, J.A. and Tavagnacco, D. and Tenti, M. and Toffolatti, L. and Tomasi, M. and Tristram, M. and Trombetti, T. and Valiviita, J. and Vansyngel, F. and Van Tent, F. and Vielva, P. and Villa, F. and Wandelt, B.D. and Wehus, I.K. and Zacchei, A. and Zonca, A. (2016) Planck intermediate results. XLIV. Structure of the Galactic magnetic field from dust polarization maps of the southern Galactic cap. Astronomy & Astrophysics, 596 . A105/1-A105/15. ISSN 1432-0746

Abstract

Using data from the Planck satellite, we study the statistical properties of interstellar dust polarization at high Galactic latitudes around the south pole (b < −60°). Our aim is to advance the understanding of the magnetized interstellar medium (ISM), and to provide a modelling framework of the polarized dust foreground for use in cosmic microwave background (CMB) component-separation procedures. We examine the Stokes I, Q, and U maps at 353 GHz, and particularly the statistical distribution of the polarization fraction (p) and angle (ψ), in order to characterize the ordered and turbulent components of the Galactic magnetic field (GMF) in the solar neighbourhood. The Q and U maps show patterns at large angular scales, which we relate to the mean orientation of the GMF towards Galactic coordinates (l0,b0) = (70° ± 5°,24° ± 5°). The histogram of the observed p values shows a wide dispersion up to 25%. The histogram of ψ has a standard deviation of 12° about the regular pattern expected from the ordered GMF. We build a phenomenological model that connects the distributions of p and ψ to a statistical description of the turbulent component of the GMF, assuming a uniform effective polarization fraction (p0) of dust emission. To compute the Stokes parameters, we approximate the integration along the line of sight (LOS) as a sum over a set of N independent polarization layers, in each of which the turbulent component of the GMF is obtained from Gaussian realizations of a power-law power spectrum. We are able to reproduce the observed p and ψ distributions using a p0 value of 26%, a ratio of 0.9 between the strengths of the turbulent and mean components of the GMF, and a small value of N. The mean value of p (inferred from the fit of the large-scale patterns in the Stokes maps) is 12 ± 1%. We relate the polarization layers to the density structure and to the correlation length of the GMF along the LOS. We emphasize the simplicity of our model (involving only a few parameters), which can be easily computed on the celestial sphere to produce simulated maps of dust polarization. Our work is an important step towards a model that can be used to assess the accuracy of component-separation methods in present and future CMB experiments designed to search the B mode CMB polarization from primordial gravity waves.

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