Analyzing the Intrinsic Magnetic Field in the Galactic Center Radio Arc

TL;DR

This study investigates the complex magnetic field patterns in the Galactic Center Radio Arc NTFs, revealing the influence of external and internal Faraday effects and suggesting local structures may impact magnetic orientations.

Contribution

It provides the first detailed spectro-polarimetric analysis of the Radio Arc NTFs, identifying the roles of external and internal Faraday effects in magnetic field rotation.

Findings

External Faraday effects likely cause the observed magnetic rotation.

Internal Faraday effects are probable in regions with parallel magnetic fields.

Local structures, such as the Radio Shell, may influence magnetic field patterns.

Abstract

The Radio Arc is a system of organized non-thermal filaments (NTFs) located within the Galactic Center (GC) region of the Milky Way. Recent observations of the Radio Arc NTFs revealed a magnetic field which alternates between being parallel and rotated with respect to the orientation of the filaments. This pattern is in stark contrast to the predominantly parallel magnetic field orientations observed in other GC NTFs. To help elucidate the origin of this pattern, we analyze spectro-polarimetric data of the Radio Arc NTFs using an Australian Telescope Compact Array data set covering the continuous frequency range from $\sim$4 to 11 GHz at a spectral resolution of 2 MHz. We fit depolarization models to the spectral polarization data to characterize Faraday effects along the line-of-sight. We assess whether structures local to the Radio Arc NTFs may contribute to the unusual magnetic field orientation. External Faraday effects are identified as the most likely origin of the rotation observed for the Radio Arc NTFs; however, internal Faraday effects are also found to be likely in regions of parallel magnetic field. The increased likelihood of internal Faraday effects in parallel magnetic field regions may be attributed to the effects of structures local to the GC. One such structure could be the Radio Shell local to the Radio Arc NTFs. Future studies are needed to determine whether this alternating magnetic field pattern is present in other multi-stranded NTFs, or is a unique property resulting from the complex interstellar region local to the Radio Arc NTFs.