Faraday dispersion functions of galaxies
  The Faraday dispersion function (FDF), which can be derived from an observed
polarization spec- trum by Faraday rotation measure synthesis, is a profile of
polarized emissions as a function of Faraday depth. We study intrinsic FDFs
along sight lines through face-on, Milky-Way-like galaxies by means of a
sophisticated galactic model incorporating 3D MHD turbulence, and investigate
how much the FDF contains information intrinsically. Since the FDF reflects
distributions of thermal and cosmic- ray electrons as well as magnetic fields,
it has been expected that the FDF could be a new probe to examine internal
structures of galaxies. We, however, find that an intrinsic FDF along a sight
line through a galaxy is very complicated, depending significantly on actual
configurations of turbulence. We perform 800 realizations of turbulence, and
find no universal shape of the FDF even if we fix the global parameters of the
model. We calculate the probability distribution functions of the standard
deviation, skewness, and kurtosis of FDFs and compare them for models with
different global pa- rameters. Our models predict that the presence of vertical
magnetic fields and large scale-height of cosmic-ray electrons tend to make the
standard deviation relatively large. Contrastingly, differences in skewness and
kurtosis are relatively less significant.
