Magnetic fields in star-forming systems (II): examining dust
  polarization, the Zeeman effect, and the Faraday rotation measure as magnetic
  field tracers
  The degree to which the formation and evolution of clouds and filaments in
the interstellar medium is regulated by magnetic fields remains an open
question. Yet the fundamental properties of the fields (strength and 3D
morphology) are not readily observable. We investigate the potential for
recovering magnetic field information from dust polarization, the Zeeman
effect, and the Faraday rotation measure ($RM$) in a SILCC-Zoom
magnetohydrodynamic (MHD) filament simulation. The object is analyzed at the
onset of star formation, and it is characterized by a line-mass of about M/L
$\sim 63\ M_{\odot}\ pc^{-1}$ out to a radius of $1\,$pc and a kinked 3D
magnetic field morphology. We generate synthetic observations via POLARIS
radiative transfer (RT) post-processing, and compare with an analytical model
of helical or kinked field morphology to help interpreting the inferred
observational signatures. We show that the tracer signals originate close to
the filament spine. We find regions along the filament where the
angular-dependency with the line-of-sight (LOS) is the dominant factor and dust
polarization may trace the underlying kinked magnetic field morphology. We also
find that reversals in the recovered magnetic field direction are not
unambiguously associated to any particular morphology. Other physical
parameters, such as density or temperature, are relevant and sometimes dominant
compared to the magnetic field structure in modulating the observed signal. We
demonstrate that the Zeeman effect and the $RM$ recover the line-of-sight
magnetic field strength to within a factor 2.1 - 3.4. We conclude that the
magnetic field morphology may not be unambiguously determined in low-mass
systems by observations of dust polarization, Zeeman effect, or $RM$, whereas
the field strengths can be reliably recovered.
