S315p.180 — Polarized thermal dust emission from Planck, a comparison with MHD simulations and lessons from a fBm model

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Aug 4th at 6:00 PM until 6:00 PM

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Author(s): François Levrier1

Institution(s): 1. LERMA/LRA, ENS Paris / Observatoire de Paris / UPMC

The Planck satellite has mapped the polarized microwave sky (from 30 GHz to 353 GHz) with unprecedented sensitivity and angular resolution. This wealth of data yields the first complete map of polarized thermal emission from dust in our own Galaxy, shedding new light on the formation of dense cold structures within which new stars and planetary systems are born, under the combined effects of gravity, turbulence and magnetic fields. On behalf of the Planck Collaboration, I will present a statistical analysis of this polarized emission from nearby molecular clouds, focusing first on the evolution of the maximum polarization fraction observed as a function of column density, and on the anti-correlation between the polarization fraction and the local dispersion of polarization angles. To interpret this data, I will present numerical simulations of anisotropic MHD turbulence and show the essential role played by the topology of the interstellar magnetic field, in particular its large-scale component. To extend the analysis beyond the polarization fraction and angle, I will present the one-point and two-point statistics of Stokes Q and U, showing in particular how changes in magnetic field direction lead to multimodality in the (Q,U) distributions. Finally, using the results of a numerical experiment with fractional Brownian motion (fBm) fields, I will exhibit the observables best suited to retrieve the spectral index of the turbulent component of the interstellar magnetic field.