Magnetic structure of our Galaxy: A review of observations

TL;DR

This review summarizes recent observational advances in mapping the magnetic structure of the Milky Way across its disk, center, and halo, highlighting methods, findings, and remaining gaps in understanding.

Contribution

It consolidates diverse observational data to provide a comprehensive overview of the Galaxy's magnetic field structure and identifies areas needing further investigation.

Findings

Magnetic fields in the disk are mapped by polarization, Zeeman splitting, and pulsar measures.

Galactic center shows non-thermal filaments indicating poloidal fields, with uncertain field strength.

Halo magnetic fields exhibit large-scale toroidal patterns with reversed directions above and below the plane.

Abstract

The magnetic structure in the Galactic disk, the Galactic center and the Galactic halo can be delineated more clearly than ever before. In the Galactic disk, the magnetic structure has been revealed by starlight polarization within 2 or 3 kpc of the Solar vicinity, by the distribution of the Zeeman splitting of OH masers in two or three nearby spiral arms, and by pulsar dispersion measures and rotation measures in nearly half of the disk. The polarized thermal dust emission of clouds at infrared, mm and submm wavelengths and the diffuse synchrotron emission are also related to the large-scale magnetic field in the disk. The rotation measures of extragalactic radio sources at low Galactic latitudes can be modeled by electron distributions and large-scale magnetic fields. The statistical properties of the magnetized interstellar medium at various scales have been studied using rotation measure data and polarization data. In the Galactic center, the non-thermal filaments indicate poloidal fields. There is no consensus on the field strength, maybe mG, maybe tens of uG. The polarized dust emission and much enhanced rotation measures of background radio sources are probably related to toroidal fields. In the Galactic halo, the antisymmetric RM sky reveals large-scale toroidal fields with reversed directions above and below the Galactic plane. Magnetic fields from all parts of our Galaxy are connected to form a global field structure. More observations are needed to explore the untouched regions and delineate how fields in different parts are connected.