Dylan Paré (University of Iowa)

Dylan Paré Colloquium: A VLA Polarimetric Study of the Galactic Center Radio Arc

Marsfield Lecture Theatre

Abstract

The Galactic Center (GC) is a unique observational target containing molecular cloud densities, magnetic field strengths, and gas temperatures more extreme than found elsewhere in the Galaxy. One way to study the properties of the strong magnetic field in this region is to analyze the unique non-thermal filaments (NTFs) -- extended, synchrotron-emitting structures. The most prominent set of NTFs is known as the Radio Arc. I conducted a radio polarimetric study of the Radio Arc utilizing the S-, C-, and X-bands of the upgraded Very Large Array interferometer, providing a multi-GHz frequency range with hundreds of channels. In this talk I present the results of this study and compare my findings with those obtained for other NTFs in the GC. The total intensity distributions reveal large-scale helical features that surround the Arc NTFs, very narrow sub-filamentation within the Arc NTFs, and compact sources along the NTFs. The polarized intensity is confined within a 4’ region of the Arc NTFs and there are elongated polarized structure that appear to lack total intensity counterparts. RM values towards the Radio Arc range from -500 to -5800 rad m-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 Radio Arc shows an ordered pattern that is rotated by about 60° to the extent of the NTFs. This changing pattern may be caused by an additional magnetized local to the Radio Arc, so that we observe two field systems superposed in our observations. The large-scale helical segments near the Radio Arc could be components of such a source causing these changes in intrinsic magnetic field, as well as some variations in the polarization and rotation measure values along the NTFs.