Connecting the interstellar magnetic field at the heliosphere to the Loop I superbubble

P C Frisch,D B Seriacopi,D J Mccomas,H O Funsten,A M Magalhaes,V Piirola,S J Wiktorowicz,N A Schwadron,A Berdyugin

doi:10.1088/1742-6596/577/1/012010

Abstract

The local interstellar magnetic field affects both the heliosphere and the surrounding cluster of interstellar clouds (CLIC). Measurements of linearly polarized starlight provide the only test of the magnetic field threading the CLIC. Polarization measurements of the CLIC magnetic field show multiple local magnetic structures, one of which is aligned with the magnetic field traced by the center of the "ribbon" of energetic neutral atoms discovered by the Interstellar Boundary Explorer (IBEX). Comparisons between the bulk motion of the CLIC through the local standard of rest, the magnetic field direction, the geometric center of Loop I, and the polarized dust bridge extending from the heliosphere toward the North Polar Spur direction all suggest that the CLIC is part of the rim region of the Loop I superbubble.

Highlights

Origin of local interstellar magnetic fieldThe Sun resides in a region of space with very low interstellar densities [20] that is offset by ∼ 400 pc from the density maximum of the Orion spiral arm ( known as the Orion Spur, 9)
The local interstellar magnetic field affects both the heliosphere and the surrounding cluster of interstellar clouds (CLIC)
The property that the optical polarization vectors are perpendicular to the Loop I synchrotron polarizations, and perpendicular to polarized infrared light from dust associated with Loop I [42; 43], shows that the position angles of polarized starlight trace the magnetic field directions in the global diffuse interstellar medium, and that the linearly polarized starlight has a plane of polarization that is parallel to the magnetic field direction

Summary

Origin of local interstellar magnetic field

The Sun resides in a region of space with very low interstellar densities [20] that is offset by ∼ 400 pc from the density maximum of the Orion spiral arm ( known as the Orion Spur, 9). The property that the optical polarization vectors are perpendicular to the Loop I synchrotron polarizations (e.g. compare polarization maps in references [39and [4]), and perpendicular to polarized infrared light from dust associated with Loop I [42; 43], shows that the position angles of polarized starlight trace the magnetic field directions in the global diffuse interstellar medium, and that the linearly polarized starlight has a plane of polarization that is parallel to the magnetic field direction This property enables the mapping of the local ISMF direction using high-sensitivity polarization measurements, ≤ 0.01% [2; 14; 18; 21; 22]. Dust extinction and polarization strengths jump at 100 ± 20 pc where l < 40◦, and at 280 ± 50 pc where 360◦ < l < 270◦, indicating that the densest parts of Loop I extend closest to the Sun for longitudes < 40◦

Location of the heliosphere in the rim of Loop I

Interstellar magnetic field shaping the heliosphere

Structure in the local interstellar magnetic field

What is an interstellar cloud?

Conclusions