Constraining models of the large scale Galactic magnetic field with WMAP5 polarization data and extragalactic Rotation Measure sources

Understand

We introduce a method to quantify the quality-of-fit between data and observables depending on the large scale Galactic magnetic field.

• We combine WMAP5 polarized synchrotron data and Rotation Measures of extragalactic sources in a joint analysis to obtain best fit parameters and confidence levels for GMF models common in the literature.
• None of the existing models provide a good fit in both the disk and halo regions, and in many instances best-fit parameters are quite different than the original values.
• We note that probing a very large parameter space is necessary to avoid false likelihood maxima.