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

TL;DR

This paper presents a new method to evaluate and constrain models of the large-scale Galactic magnetic field using WMAP5 polarization data and extragalactic Rotation Measure sources, revealing that existing models do not fit well in all regions.

Contribution

It introduces a joint analysis approach combining different data sets to assess and improve Galactic magnetic field models, highlighting the importance of extensive parameter space exploration.

Findings

Existing GMF models do not fit both disk and halo regions well.

Best-fit parameters often differ significantly from original values.

Electron density characteristics can be constrained with current data.

Abstract

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. The thermal and relativistic electron densities are critical for determining the GMF from the observables but they are not well constrained. We show that some characteristics of the electron densities can already be constrained using our method and with future data it may be possible to carry out a self-consistent analysis in which models of the GMF and electron densities are simultaneously optimized.