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Planck 2018 results. XII. Galactic astrophysics using polarized dust emission

Aghanim, N. and Ghosh, T. and Bock, J. J. and Crill, B. P. and Doré, O. and Helou, G. and Rocha, G. and Chary, R.-R. and Górski, K. M. and Lawrence, C. R. and Roudier, G. (2020) Planck 2018 results. XII. Galactic astrophysics using polarized dust emission. Astronomy and Astrophysics, 641 . Art. No. A12. ISSN 0004-6361.

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Observations of the submillimetre emission from Galactic dust, in both total intensity I and polarization, have received tremendous interest thanks to the Planck full-sky maps. In this paper we make use of such full-sky maps of dust polarized emission produced from the third public release of Planck data. As the basis for expanding on astrophysical studies of the polarized thermal emission from Galactic dust, we present full-sky maps of the dust polarization fraction p, polarization angle ψ, and dispersion function of polarization angles S. The joint distribution (one-point statistics) of p and N_H confirms that the mean and maximum polarization fractions decrease with increasing N_H. The uncertainty on the maximum observed polarization fraction, p_(max) = 22.0_(−1.4)^(+3.5)% at 353 GHz and 80′ resolution, is dominated by the uncertainty on the Galactic emission zero level in total intensity, in particular towards diffuse lines of sight at high Galactic latitudes. Furthermore, the inverse behaviour between p and S found earlier is seen to be present at high latitudes. This follows the S ∝ p⁻¹ relationship expected from models of the polarized sky (including numerical simulations of magnetohydrodynamical turbulence) that include effects from only the topology of the turbulent magnetic field, but otherwise have uniform alignment and dust properties. Thus, the statistical properties of p, ψ, and S for the most part reflect the structure of the Galactic magnetic field. Nevertheless, we search for potential signatures of varying grain alignment and dust properties. First, we analyse the product map S × p, looking for residual trends. While the polarization fraction p decreases by a factor of 3−4 between N_H = 10²⁰ cm⁻² and N_H = 2 × 1022 cm⁻², out of the Galactic plane, this product S × p only decreases by about 25%. Because S is independent of the grain alignment efficiency, this demonstrates that the systematic decrease in p with N_H is determined mostly by the magnetic-field structure and not by a drop in grain alignment. This systematic trend is observed both in the diffuse interstellar medium (ISM) and in molecular clouds of the Gould Belt. Second, we look for a dependence of polarization properties on the dust temperature, as we would expect from the radiative alignment torque (RAT) theory. We find no systematic trend of S × p with the dust temperature T_d, whether in the diffuse ISM or in the molecular clouds of the Gould Belt. In the diffuse ISM, lines of sight with high polarization fraction p and low polarization angle dispersion S tend, on the contrary, to have colder dust than lines of sight with low p and high S. We also compare the Planck thermal dust polarization with starlight polarization data in the visible at high Galactic latitudes. The agreement in polarization angles is remarkable, and is consistent with what we expect from the noise and the observed dispersion of polarization angles in the visible on the scale of the Planck beam. The two polarization emission-to-extinction ratios, R_(P/p) and R_(S/V), which primarily characterize dust optical properties, have only a weak dependence on the column density, and converge towards the values previously determined for translucent lines of sight. We also determine an upper limit for the polarization fraction in extinction, p_V/E(B − V), of 13% at high Galactic latitude, compatible with the polarization fraction p ≈ 20% observed at 353 GHz. Taken together, these results provide strong constraints for models of Galactic dust in diffuse gas.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Aghanim, N.0000-0002-6688-8992
Bock, J. J.0000-0002-5710-5212
Crill, B. P.0000-0002-4650-8518
Doré, O.0000-0002-5009-7563
Helou, G.0000-0003-3367-3415
Rocha, G.0000-0002-4150-8076
Chary, R.-R.0000-0001-7583-0621
Additional Information:© 2020 Planck Collaboration. Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Received 16 July 2018; Accepted 28 February 2019; Published online 11 September 2020. Planck ( is a project of the European Space Agency (ESA) with instruments provided by two scientific consortia funded by ESA member states and led by Principal Investigators from France and Italy, telescope reflectors provided through a collaboration between ESA and a scientific consortium led and funded by Denmark, and additional contributions from NASA (USA). The Planck Collaboration acknowledges the support of ESA; CNES, and CNRS/INSU-IN2P3-INP (France); ASI, CNR, and INAF (Italy); NASA and DoE (USA); STFC and UKSA (UK); CSIC, MINECO, 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); ERC and PRACE (EU). A description of the Planck Collaboration and a list of its members, indicating which technical or scientific activities they have been involved in, can be found at This work has made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC, Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. The research leading to these results has received funding from the European Research Council under the European Union’s Horizon 2020 Research & Innovation Framework Programme/ERC grant agreement ERC-2016-ADG-742719. This research has received funding from the Agence Nationale de la Recherche (ANR-17-CE31-0022). We thank Pekka Teerikorpi and Andrei Berdyugin for kindly providing stellar polarization data and providing insights on stellar polarization references, Gina Panopoulou for discussions of the zero point calibration of the polarization angle, and Ralf Siebenmorgen and Nikolai Voshchinnikov for statistical discussions. We gratefully acknowledge the help of Rosine Lallement regarding the handling of the Gaia data.
Group:Infrared Processing and Analysis Center (IPAC), Astronomy Department
Funding AgencyGrant Number
European Space Agency (ESA)UNSPECIFIED
Centre National d'Études Spatiales (CNES)UNSPECIFIED
Centre National de la Recherche Scientifique (CNRS)UNSPECIFIED
Institut National des Sciences de l'Univers (INSU)UNSPECIFIED
Agenzia Spaziale Italiana (ASI)UNSPECIFIED
Consiglio Nazionale delle Ricerche (CNR)UNSPECIFIED
Istituto Nazionale di Astrofisica (INAF)UNSPECIFIED
Department of Energy (DOE)UNSPECIFIED
Science and Technology Facilities Council (STFC)UNSPECIFIED
United Kingdom Space Agency (UKSA)UNSPECIFIED
Consejo Superior de Investigaciones Científicas (CSIC)UNSPECIFIED
Ministerio de Economía, Industria y Competitividad (MINECO)UNSPECIFIED
Junta de AndalucíaUNSPECIFIED
Spanish Supercomputing Network (RES)UNSPECIFIED
Finnish Ministry of Employment and the EconomyUNSPECIFIED
Academy of FinlandUNSPECIFIED
Finnish IT Center for Science (CSC)UNSPECIFIED
Deutsches Zentrum für Luft- und Raumfahrt (DLR)UNSPECIFIED
Max Planck SocietyUNSPECIFIED
Canadian Space Agency (CSA)UNSPECIFIED
State Secretariat for Education and Research (Switzerland) UNSPECIFIED
Swiss Space Office (SSO)UNSPECIFIED
Research Council of NorwayUNSPECIFIED
Science Foundation, IrelandUNSPECIFIED
Fundação para a Ciência e a Tecnologia (FCT)UNSPECIFIED
Ministério da Ciência, Tecnologia e Ensino Superior (MCTES)UNSPECIFIED
European Research Council (ERC)742719
Partnership for Advanced Computing in Europe (PRACE)UNSPECIFIED
Gaia Multilateral AgreementUNSPECIFIED
Agence Nationale pour la Recherche (ANR)ANR-17-CE31-0022
Subject Keywords:polarization – magnetic fields – turbulence – dust, extinction – local insterstellar matter – submillimeter: ISM
Record Number:CaltechAUTHORS:20190627-085435272
Persistent URL:
Official Citation:Planck 2018 results - XII. Galactic astrophysics using polarized dust emission. Planck Collaboration, N. Aghanim, et. al., A&A, 641 (2020) A12; DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:96767
Deposited By: Tony Diaz
Deposited On:27 Jun 2019 16:11
Last Modified:14 Sep 2020 16:51

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