Planck intermediate results. XX. Comparison of polarized thermal emission from Galactic dust with simulations of MHD turbulence
Abstract
Polarized emission observed by Planck HFI at 353 GHz towards a sample of nearby fields is presented, focusing on the statistics of polarization fractions p and angles ψ. 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.
Additional Information
© 2015 ESO. Article published by EDP Sciences. Received 28 April 2014; Accepted 4 September 2014; Published online 13 April 2015. The development of Planck has been supported by: ESA; CNES and CNRS/INSU-IN2P3-INP (France); ASI, CNR, and INAF (Italy); NASA and DoE (USA); STFC and UKSA (UK); CSIC, MICINN, JA and RES (Spain); Tekes, AoF and CSC (Finland); DLR and MPG (Germany); CSA (Canada); DTU Space (Denmark); SER/SSO (Switzerland); RCN (Norway); SFI (Ireland); FCT/MCTES (Portugal); and PRACE (EU). A description of the Planck Collaboration and a list of its members, including the technical or scientific activities in which they have been involved, can be found at http://www.sciops.esa.int/index.php?project=planck&page=Planck_Collaboration. Some of the results in this paper have been derived using the HEALPix package. The authors would like to thank Charles Beichman for his careful reading of the manuscript and useful comments. The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013) / ERC grant agreement No. 267934.Attached Files
Published - aa24086-14.pdf
Accepted Version - 1405.0872.pdf
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Additional details
- Eprint ID
- 96861
- Resolver ID
- CaltechAUTHORS:20190701-105706574
- European Space Agency (ESA)
- Centre National d'Études Spatiales (CNES)
- Centre National de la Recherche Scientifique (CNRS)
- Institut National des Sciences de l'Univers (INSU)
- Agenzia Spaziale Italiana (ASI)
- Consiglio Nazionale delle Ricerche (CNR)
- Istituto Nazionale di Astrofisica (INAF)
- NASA
- Department of Energy (DOE)
- Science and Technology Facilities Council (STFC)
- United Kingdom Space Agency (UKSA)
- Consejo Superior de Investigaciones Científicas (CSIC)
- Ministerio de Economía, Industria y Competitividad (MINECO)
- Junta de Andalucía
- Spanish Supercomputing Network (RES)
- Finnish Ministry of Employment and the Economy
- Academy of Finland
- Finnish IT Center for Science (CSC)
- Deutsches Zentrum für Luft- und Raumfahrt (DLR)
- Max Planck Society
- Canadian Space Agency (CSA)
- DTU Space (Denmark)
- State Secretariat for Education and Research (Switzerland)
- Swiss Space Office (SSO)
- Research Council of Norway
- Science Foundation, Ireland
- Fundação para a Ciência e a Tecnologia (FCT)
- Ministério da Ciência, Tecnologia e Ensino Superior (MCTES)
- Partnership for Advanced Computing in Europe (PRACE)
- 267934
- European Research Council (ERC)
- Created
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2019-07-02Created from EPrint's datestamp field
- Updated
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2023-03-15Created from EPrint's last_modified field
- Caltech groups
- Infrared Processing and Analysis Center (IPAC)