Radiative transfer with POLARIS. II.: Modeling of synthetic Galactic
  synchrotron observations
  We present an updated version of POLARIS, a well established code designated
for dust polarisation and line radiative transfer (RT) in arbitrary
astrophysical environments. We extend the already available capabilities with a
synchrotron feature for polarised emission. Here, we combine state-of-the-art
solutions of the synchrotron RT coefficients with numerical methods for solving
the complete system of equations of the RT problem, including Faraday rotation
(FR) as well as Faraday conversion (FC). We validate the code against Galactic
and extragalactic observations by performing a statistical analysis of
synthetic all-sky synchrotron maps for positions within the galaxy and for
extragalactic observations. For these test scenarios we apply a model of the
Milky Way based on sophisticated magneto-hydrodynamic (MHD) simulations and
population-synthesis post-processing techniques.We explore different parameters
for modeling the distribution of free electrons and for a turbulent magnetic
field component. We find that a strongly fluctuating field is necessary for
simulating synthetic synchrotron observations on small scales, we argue that
Faraday rotation alone can account for the depolarisation of the synchrotron
signal, and we discuss the importance of the observer position within the Milky
Way. Altogether, we conclude that POLARIS is a highly reliable tool for
predicting synchrotron emission and polarisation, including Faraday rotation in
a realistic galactic context. It can thus contribute to better understand the
results from current and future observational missions.
