relatively less significant.'
author:
- 'Shinsuke Ideguchi$^1$, Yuichi Tashiro$^1$, Takuya Akahori$^2$, Keitaro Takahashi$^1$, and Dongsu Ryu$^3$'
title: Faraday Dispersion Functions of Galaxies
---

Introduction {#section1}
============

The origin and nature of magnetic fields in spiral galaxies is a longstanding problem [see e.g., @smk10]. Faraday rotation measure (RM) obtained by radio polarimetry is an important probe to examine structures of galactic magnetic fields [e.g., @gae05; @bec09]. RM can be obtained as a proportionality constant between the polarization angle and the squared wavelength, if only a single polarization source is present along the line of sight (LOS). Inside galaxies, however, there are multiple sources in general. The relation thus becomes more complicated and is hard to be interpreted [@bu66; @br05]. A more sophisticated method is needed to be developed.

Faraday RM synthesis [@bu66; @br05] is an alternative method to interpret radio polarimetry data. Using Faraday RM synthesis, we can transform an observed polarization spectrum into the so-called Faraday dispersion function (FDF), which includes information of polarized sources along the LOS. Faraday RM synthesis has been applied only recently, since a wideband polarization spectrum is needed to ensure reasonable transformation into the FDF. Up to now, there are several observations of FDFs in 