Planck intermediate results. XIX. An overview of the polarized thermal emission from Galactic dust
Collaboration
33 pages
Published in:
- Astron.Astrophys. 576 (2015) A104
- Published: Apr 13, 2015
e-Print:
- 1405.0871 [astro-ph.GA]
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Abstract: (EDP Sciences)
This paper presents an overview of the polarized sky as seen by PlanckHFI at 353 GHz, whichis the most sensitive Planck channel for dust polarization. We constructand analyse maps of dust polarization fraction and polarization angle at 1deg. resolution, taking into account noise biasand possible systematic effects. The sensitivity of the Planck HFIpolarization measurements allows for the first time a mapping of Galactic dust polarizedemission on large scales, including low column density regions. We find that the maximumobserved dust polarization fraction is high (p_max = 19.8%), in particular in someregions of moderate hydrogen column density (N_H ). The polarization fraction displays a large scatter atN_H below a few 10^21 cm^-2. There is ageneral decrease in the dust polarization fraction with increasing column density aboveN_H ≃ 1 x10^21 cm^-2 and in particular a sharp drop aboveN_H ≃ 1.5 x10^22 cm^-2. We characterize the spatialstructure of the polarization angle using the angle dispersion function. We find that thepolarization angle is ordered over extended areas of several square degrees, separated byfilamentary structures of high angle dispersion function. These appear as interfaces wherethe sky projection of the magnetic field changes abruptly without variations in the columndensity. The polarization fraction is found to be anti-correlated with the dispersion ofpolarization angles. These results suggest that, at the resolution of 1deg., depolarization is due mainly tofluctuations in the magnetic field orientation along the line of sight, rather than to theloss of grain alignment in shielded regions. We also compare the polarization of thermaldust emission with that of synchrotron measured with Planck,low-frequency radio data, and Faraday rotation measurements toward extragalactic sources.These components bear resemblance along the Galactic plane and in some regions such as theFan and North Polar Spur regions. The poor match observed in other regions shows, however,that dust, cosmic-ray electrons, and thermal electrons generally sample different parts ofthe line of sight.- ISM: general
- dust, extinction
- ISM: magnetic fields
- ISM: clouds
- submillimeter: ISM
References(111)
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