Magnetically aligned straight depolarisation canals and the rolling Hough transform

TL;DR

This study uses the rolling Hough transform to analyze straight depolarization canals in LOFAR radio data, revealing their alignment with magnetic fields and their relation to interstellar medium structures.

Contribution

It introduces the application of the rolling Hough transform to characterize depolarization canals and compares their orientations with magnetic field tracers in the ISM.

Findings

Depolarization canals and Hi filaments are inclined by about 10° to the Galactic plane.

Canal orientations align with magnetic field directions from Planck dust polarization.

A distinct 65° orientation correlates with a bar-like structure in the 3C 196 field.

Abstract

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.