Faraday dispersion function of disk galaxies with axisymmetric global magnetic fields I

Abstract

Faraday tomography is a novel method to probe 3-dimensional structure of magnetic fields of polarized radio sources. In this paper, we investigate Faraday dispersion function (FDF) of disk galaxies extending a simple analytic model of galactic magnetic fields developed in Ideguchi et al. (2017). The model consists of axisymmetric coherent fields and turbulent fields and we consider the effects of inclination, relative amplitude of coherent and turbulent magnetic fields and pitch angle of coherent fields. Our simple model makes it easy to obtain physical interpretation of FDFs and helps understanding observational results. We find FDFs have two peaks when galaxies are observed with non zero inclination. The gap and relative height of two peaks are dependent on the inclination angle and pitch angle but are not affected by relative amplitude of coherent and turbulent magnetic fields so much. These findings give us an important caution that two peaks in observed FDFs do not necessarily imply the presence of two separate radio sources within a beam.