Separation of anomalous and synchrotron emissions using WMAP polarization data
Institut d'Astrophysique Spatiale (CNRS), Université Paris-Sud, Bât. 121, 91405 Orsay, France e-mail: email@example.com
2 Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON, M5S 3H8, Canada
3 LPSC, Université Joseph Fourier Grenoble 1, CNRS/IN2P3, Institut National Polytechnique de Grenoble, 53 Av. des Martyrs, 38026 Grenoble, France
4 Centre d'Étude Spatiale des Rayonnements, 9 Av. du Colonel Roche, 31028 Toulouse, France
Accepted: 10 September 2008
Context. Apart from its contribution to cosmology, the WMAP data brings new information on the Galactic interstellar medium. In particular the polarization data provide constraints on the Galactic magnetic field and the synchrotron emission, while the intensity data can be used to study the anomalous microwave emission.
Aims. The main goals of this study is to use the information from both WMAP intensity and polarization data to do a separation of the Galactic components, with a focus on the synchrotron and anomalous emissions.
Methods. Our analysis is made at 23 GHz where the signal-to-noise ratio is the highest and the estimate of the CMB map is less critical. Our estimate of the synchrotron intensity is based on an extrapolation of the Haslam 408 MHz data with a spatially varying spectral index constrained by the WMAP 23 GHz polarization data and a bi-symmetrical spiral model of the galactic magnetic field with a turbulent part following a –5/3 power law spectrum.
Results. The 23 GHz polarization data are found to be compatible with a magnetic field with a pitch angle and an amplitude of the turbulent part of the magnetic field 0.57 times the local value of the field, in agreement with what is found using rotation measures of pulsars and polarized extinction by dust. The synchrotron spectral index between 408 MHz and 23 GHz obtained from polarization data and our model of the magnetic field has a mean value of with a limited spatial variation with a standard deviation of 0.06. When thermal dust, free-free and synchrotron are removed from the WMAP intensity data, the residual anomalous emission is highly correlated with thermal dust emission with a spectrum in agreement with spinning dust models.
Conclusions. Considering a classical model of the large scale Galactic magnetic field, we show that the polarization data of WMAP are in favor of a soft synchrotron intensity highly correlated with the 408 MHz data. Furthermore the combination of the WMAP polarization and intensity data brings strong evidence for the presence of unpolarized spinning dust emission in the 20–60 GHz range. In preparation for the Planck mission this joint analysis of polarization and intensity data opens new perspective on the study of the Galactic interstellar medium and on the component separation exercise.
Key words: ISM: magnetic fields / radio continuum: ISM / turbulence / polarization / dust, extinction
© ESO, 2008