Magnetic arms of NGC6946 traced in the Faraday cubes at low radio frequencies

TL;DR

This paper introduces a wavelet-based method to analyze large-scale galactic magnetic fields in low-frequency radio data, overcoming Faraday dispersion effects that obscure these structures.

Contribution

The authors develop a wavelet transform technique to decompose Faraday data cubes, revealing magnetic field structures at large scales in low-frequency radio observations.

Findings

Magnetic arms in NGC 6946 are visible at long wavelengths using the new method.

Wavelet decomposition isolates large-scale magnetic field patterns.

The approach enhances the analysis of galactic magnetic fields with future radio telescopes.

Abstract

Magnetic fields in galaxies exist on various spatial scales. Large-scale magnetic fields are thought to be generated by the $\alpha-\Omega$ dynamo. Small-scale galactic magnetic fields (1 kpc and below) can be generated by tangling the large-scale field or by the small-scale turbulent dynamo. The analysis of field structures with the help of polarized radio continuum emission is hampered by the effect of Faraday dispersion (due to fluctuations in magnetic field and/or thermal electron density) that shifts signals from large to small scales. At long observation wavelengths large-scale magnetic fields may become invisible, as in the case of spectro-polarimetric data cube of the spiral galaxy NGC~6946 observed with the Westerbork Radio Synthesis Telescope in the wavelength range 17-23 cm. The application of RM Synthesis alone does not overcome this problem. We propose to decompose the Faraday data cube into data cubes at different spatial scales by a wavelet transform. Signatures of the `magnetic arms' observed in NGC~6946 at shorter wavelengths become visible. Our method allows us to search for large-scale field patterns in data cubes at long wavelengths, as provided by new-generation radio telescopes.