Planck intermediate results. XXI. Comparison of polarized thermal emission from Galactic dust at 353 GHz with interstellar polarization in the visible
Publication date: 14 April 2015
Authors: Planck Collaboration
Journal: Astronomy & Astrophysics
Volume: 576, April 2015
Copyright: ESO, 2015
The Planck survey provides unprecedented full-sky coverage of the submillimetre polarized emission from Galactic dust. In addition to the information on the direction of the Galactic magnetic field, this also brings new constraints on the properties of dust. The dust grains that emit the radiation seen by Planck in the submillimetre also extinguish and polarize starlight in the visible. Comparison of the polarization of the emission and of the interstellar polarization on selected lines of sight probed by stars provides unique new diagnostics of the emission and light scattering properties of dust, and therefore of the important dust model parameters, composition, size, and shape. Using ancillary catalogues of interstellar polarization and extinction of starlight, we obtain the degree of polarization, pV, and the optical depth in the V band to the star, τV. Toward these stars we measure the submillimetre polarized intensity, PS, and total intensity, IS, in the Planck 353 GHz channel. We compare the column density measure in the visible, E(B − V), with that inferred from the Planck product map of the submillimetre dust optical depth and compare the polarization direction (position angle) in the visible with that in the submillimetre. For those lines of sight through the diffuse interstellar medium with comparable values of the estimated column density and polarization directions close to orthogonal, we correlate properties in the submillimetre and visible to find two ratios, RS/V = (PS/IS) / (pV/τV) and RP/p = PS/pV, the latter focusing directly on the polarization properties of the aligned grain population alone.
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