A VLA Polarimetric Study of the Galactic Center Radio Arc: Characterizing Polarization, Rotation Measure, and Magnetic Field Properties

TL;DR

This study uses VLA polarimetric observations to analyze the magnetic field structure, polarization, and rotation measure of the Galactic Center Radio Arc, revealing complex magnetic configurations and external Faraday rotation effects.

Contribution

It provides detailed polarization and magnetic field measurements of the Radio Arc NTFs, highlighting the presence of helical features and superposed magnetic field systems.

Findings

Detected a wide range of rotation measures from -1000 to -5800 rad/m^2.

Found intrinsic magnetic fields generally follow NTFs but show rotated patterns.

Identified large-scale helical structures possibly caused by an external magnetized source.

Abstract

The Radio Arc is one of the brightest systems of non-thermal filaments (NTFs) in the Galactic Center, located near several prominent HII regions (Sickle and Pistol) and the Quintuplet stellar cluster. We present observations of the Arc NTFs using the S-, C-, and X-bands of the Very Large Array interferometer. Our images of total intensity reveal large-scale helical features that surround the Arc NTFs, very narrow sub-filamentation, and compact sources along the NTFs. The distribution of polarized intensity is confined to a relatively small area along the NTFs. There are elongated polarized structures that appear to lack total intensity counterparts. We detect a range of rotation measure values from -1000 to -5800 rad m$\rm^{-2}$, likely caused by external Faraday rotation along the line of sight. After correcting for Faraday rotation, the intrinsic magnetic field orientation is found to generally trace the extent of the NTFs. However, the intrinsic magnetic field in several regions of the Arc NTFs shows an ordered pattern that is rotated with respect to the extent of the NTFs. We suggest this changing pattern may be caused by an additional magnetized source along the line of sight, so that we observe two field systems superposed in our observations. We suggest that the large scale helical segments near the Radio Arc could be components of such a source causing these changes in intrinsic magnetic field, and some variations in the polarization and rotation measure values along the NTFs.