Expected constraints on the Galactic magnetic field using Planck data

Abstract

Aims. We explore the ability to constrain the Galactic magnetic field intensity and spatial distribution with the incoming data from the Planck satellite. Methods. We performed realistic simulations of the Planck observations at the polarised frequency bands from 30 to 353 GHz for two all-sky surveys in the same way that we expected to turn out for the nominal mission. These simulations include cosmic microwave background (CMB), synchrotron and thermal dust Galactic emissions and instrumental noise. (Note that systematic effects are not considered in this paper.) For the synchrotron and thermal dust Galactic emissions we used a coherent 3D model of the Galaxy that describes its matter density and the magnetic field direction and intensity. We first simulated the synchrotron and dust emissions at 408 MHz and 545 GHz, respectively, and then extrapolated them to the Planck frequency bands. Results. We performed a likelihood analysis to compare the simulated data to a set of models obtained by varying the pitch angle of the regular magnetic field spatial distribution, the relative amplitude of the turbulent magnetic field, the radial scale of the electron and dust grain distributions, and the extrapolation spectral indices for the synchrotron and thermal dust emissions. We are able to set tight constraints on all considered parameters. We also found that the observed spatial variations of the synchrotron and thermal dust spectral indices will probably not affect our ability to recover the other parameters of the model. Conclusions. From this, we conclude that the Planck satellite experiment can precisely measure the main properties of the Galactic magnetic field. For an accurate reconstruction of the matter distribution one still requires on the one hand an improved modelling of the interstellar medium and on the other hand such as extra data sets rotation measurements of pulsars. © 2012 ESO.