Magnetically aligned straight depolarisation canals and the rolling
  Hough transform
  Aims. We aim to characterize the properties of the straight depolarization
canals detected in the Low Frequency Array (LOFAR) polarimetric observations of
a field centered on the extragalactic source 3C 196. We also compare the canal
orientations with magnet- ically aligned Hi filaments and the magnetic field
probed by polarized dust emission. Methods. We used the rolling Hough transform
(RHT) to identify and characterize the orientation of the straight
depolarization canals in radio polarimetric data and the filaments in Hi data.
Results. The majority of the straight depolarization canals and the Hi
filaments are inclined by 10deg with respect to the Galactic plane and are
aligned with the plane-of-sky magnetic field orientation probed by the Planck
dust polarization data. The other distinct orientation, of 65deg with respect
to the Galactic plane, is associated with the orientation of a bar-like
structure observed in the 3C 196 field at 350 MHz. Conclusions. An alignment
between three distinct tracers of the (local) interstellar medium (ISM)
suggests that an ordered magnetic field plays a crucial role in confining
different ISM phases. The majority of the straight depolarization canals are a
result of a projection of the complicated 3D distribution of the ISM. The RHT
analysis is a robust method for identifying and characterizing the straight
depolarization canals observed in radio-polarimetric data.
