Planck intermediate results. XX. Comparison of polarized thermal emission from Galactic dust with simulations of MHD turbulence

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Ade , P A R , Juvela , M , Keihanen , E , Kurki-Suonio , H , Pelkonen , V -M , Suur-Uski , A -S , Valiviita , J & Planck Collaboration 2015 , ' Planck intermediate results. XX. Comparison of polarized thermal emission from Galactic dust with simulations of MHD turbulence ' Astronomy & Astrophysics , vol. 576 , A105 . DOI: 10.1051/0004-6361/201424086

Title: Planck intermediate results. XX. Comparison of polarized thermal emission from Galactic dust with simulations of MHD turbulence
Author: Ade, P. A. R.; Aghanim, N.; Alina, D.; Alves, M. I. R.; Aniano, G.; Annitage-Caplan, C.; Arnaud, M.; Arzoumanian, D.; Ashdown, M.; Atrio-Barandela, F.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Battaner, E.; Benabed, K.; Benoit-Levy, A.; Bernard, J. -P.; Bersanelli, M.; Bielewicz, P.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bracco, A.; Burigana, C.; Cardoso, J. -F.; Catalano, A.; Chamballu, A.; Chiang, H. C.; Christensen, P. R.; Colombi, S.; Colombo, L. P. E.; Combet, C.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; Juvela, M.; Keihanen, E.; Kurki-Suonio, H.; Pelkonen, V. -M.; Suur-Uski, A. -S.; Valiviita, J.
Contributor: University of Helsinki, Department of Physics
University of Helsinki, Particle Physics and Astrophysics
University of Helsinki, Department of Physics
University of Helsinki, Department of Astronomy (-2009)
University of Helsinki, Helsinki Institute of Physics
University of Helsinki, Helsinki Institute of Physics
Date: 2015-04
Language: eng
Number of pages: 27
Belongs to series: Astronomy & Astrophysics
ISSN: 0004-6361
URI: http://hdl.handle.net/10138/233352
Abstract: Polarized emission observed by Planck HFI at 353GHz towards a sample of nearby fields is presented, focusing on the statistics of polarization fractions p and angles psi. The polarization fractions and column densities in these nearby fields are representative of the range of values obtained over the whole sky. We find that: (i) the largest polarization fractions are reached in the most diffuse fields; (ii) the maximum polarization fraction p(max) decreases with column density N-H in the more opaque fields with N-H > 10(21) cm(-2); and (iii) the polarization fraction along a given line of sight is correlated with the local spatial coherence of the polarization angle. These observations are compared to polarized emission maps computed in simulations of anisotropic magnetohydrodynamical turbulence in which we assume a uniform intrinsic polarization fraction of the dust grains. We find that an estimate of this parameter may be recovered from the maximum polarization fraction p(max) in diffuse regions where the magnetic field is ordered on large scales and perpendicular to the line of sight. This emphasizes the impact of anisotropies of the magnetic field on the emerging polarization signal. The decrease of the maximum polarization fraction with column density in nearby molecular clouds is well reproduced in the simulations, indicating that it is essentially due to the turbulent structure of the magnetic field: an accumulation of variously polarized structures along the line of sight leads to such an anti-correlation. In the simulations, polarization fractions are also found to anti-correlate with the angle dispersion function S. However, the dispersion of the polarization angle for a given polarization fraction is found to be larger in the simulations than in the observations, suggesting a shortcoming in the physical content of these numerical models. In summary, we find that the turbulent structure of the magnetic field is able to reproduce the main statistical properties of the dust polarization as observed in a variety of nearby clouds, dense cores excluded, and that the large-scale field orientation with respect to the line of sight plays a major role in the quantitative analysis of these statistical properties.
Subject: ISM: general
dust, extinction
ISM: magnetic fields
ISM: clouds
infrared: ISM
submillimeter: ISM
RADIATIVE TORQUE ALIGNMENT
ADAPTIVE MESH REFINEMENT
MAGNETIC-FIELDS
INTERSTELLAR POLARIZATION
GRAIN ALIGNMENT
SUBMILLIMETER EMISSION
MOLECULAR CLOUDS
EFFICIENCY
TAURUS
ASSOCIATIONS
115 Astronomy, Space science
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