4.6 Article

Galactic magnetic field reconstruction using the polarized diffuse Galactic emission: formalism and application to Planck data

Journal

ASTRONOMY & ASTROPHYSICS
Volume 652, Issue -, Pages -

Publisher

EDP SCIENCES S A
DOI: 10.1051/0004-6361/201833962

Keywords

polarization; dust; extinction; submillimeter; ISM; ISM; magnetic fields; methods; statistical; cosmic background radiation

Funding

  1. European Union [687312]
  2. European Research Council under the European Union [771282]
  3. NASA Office of Space Science
  4. European Research Council (ERC) [771282] Funding Source: European Research Council (ERC)

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The study focuses on the polarized Galactic synchrotron and thermal dust emission as a key tool to understand the Galactic magnetic field. A Markov chain Monte Carlo method is used to constrain the regular GMF geometry through simulations. By analyzing Planck polarization maps, the methodology proves effective in inferring the large-scale geometrical properties of the GMF, revealing a mean pitch angle of 27 degrees with 14% scatter.
The polarized Galactic synchrotron and thermal dust emission constitutes a major tool in the study of the Galactic magnetic field (GMF) and in constraining its strength and geometry for the regular and turbulent components. In this paper, we review the modeling of these two components of the polarized Galactic emission and present our strategy for optimally exploiting the currently existing data sets. We investigate a Markov chain Monte Carlo (MCMC) method to constrain the model parameter space through maximum-likelihood analysis, focusing mainly on dust polarized emission. Relying on simulations, we demonstrate that our methodology can be used to constrain the regular GMF geometry. Fitting for the reduced Stokes parameters, this reconstruction is only marginally dependent of the accuracy of the reconstruction of the Galactic dust grain density distribution. However, the reconstruction degrades, apart from the pitch angle, when including a turbulent component on the order of the regular one as suggested by current observational constraints. Finally, we applied this methodology to a set of Planck polarization maps at 353 GHz to obtain the first MCMC based constrains on the large-scale regular-component of the GMF from the polarized diffuse Galactic thermal dust emission. By testing various models of the dust density distribution and of the GMF geometry, we prove that it is possible to infer the large-scale geometrical properties of the GMF. We obtain coherent three-dimensional views of the GMF, from which we infer a mean pitch angle of 27 degrees with 14% scatter, which is in agreement with results obtained in the literature from synchrotron emission.

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