Comparisons of the Interstellar Magnetic Field Directions obtained from the IBEX Ribbon and Interstellar Polarizations

TL;DR

This study compares interstellar magnetic field directions derived from IBEX Ribbon observations and optical polarization data, revealing a coherent local magnetic field structure with implications for local ISM origins.

Contribution

It provides a detailed comparison of ISMF directions from two different methods, highlighting their similarities and the coherence of the local magnetic field over tens of parsecs.

Findings

The best-fit magnetic pole from polarization data is within 35 degrees uncertainty.

The IBEX Ribbon and polarization directions are within 33 degrees, indicating a coherent local ISMF.

The local ISMF is nearly perpendicular to the local ISM flow, suggesting an origin related to an expanding magnetized shell.

Abstract

Variations in the spatial configuration of the interstellar magnetic field (ISMF) near the Sun can be constrained by comparing the ISMF direction at the heliosphere found from the Interstellar Boundary Explorer spacecraft (IBEX) observations of a 'Ribbon' of energetic neutral atoms (ENAs), with the ISMF direction derived from optical polarization data for stars within ~40 pc. Using interstellar polarization observations towards ~30 nearby stars within 90 deg of the heliosphere nose, we find that the best fits to the polarization position angles are obtained for a magnetic pole directed towards ecliptic coordinates of lambda, beta 263 deg, 37 deg (or galactic coordinates of L,B 38 deg, 23deg), with uncertainties of +/- 35 deg, based on the broad minimum of the best fits and the range of data quality. This magnetic pole is 33 deg from the magnetic pole that is defined by the center of the arc of the ENA Ribbon. The IBEX ENA ribbon is seen in sightlines that are perpendicular to the ISMF as it drapes over the heliosphere. The similarity of the polarization and Ribbon directions for the local ISMF suggest that the local field is coherent over scale sizes of tens of parsecs. The ISMF vector direction is nearly perpendicular to the flow of local ISM through the local standard of rest, supporting a possible local ISM origin related to an evolved expanding magnetized shell. The local ISMF direction is found to have a curious geometry with respect to the cosmic microwave background dipole moment.