A quantum mechanical approach to establishing the magnetic field orientation from a maser Zeeman profile

TL;DR

This paper clarifies the polarization conventions in maser Zeeman measurements and demonstrates that magnetic field direction can be theoretically determined from Zeeman spectra, revealing potential reversals between large-scale and small-scale magnetic fields.

Contribution

It provides a consistent polarization framework and a theoretical method to infer magnetic field orientation from Zeeman profiles, addressing previous ambiguities.

Findings

Magnetic field direction is predictable from Zeeman spectra when polarization conventions are clarified.

A potential reversal between large-scale and small-scale magnetic fields is suggested.

The approach aligns with classical Lorentzian derivations.

Abstract

Recent comparisons of magnetic field directions derived from maser Zeeman splitting with those derived from continuum source rotation measures have prompted new analysis of the propagation of the Zeeman split components, and the inferred field orientation. In order to do this, we first review differing electric field polarization conventions used in past studies. With these clearly and consistently defined, we then show that for a given Zeeman splitting spectrum, the magnetic field direction is fully determined and predictable on theoretical grounds: when a magnetic field is oriented away from the observer, the left-hand circular polarization is observed at higher frequency and the right-hand polarization at lower frequency. This is consistent with classical Lorentzian derivations. The consequent interpretation of recent measurements then raises the possibility of a reversal between the large-scale field (traced by rotation measures) and the small-scale field (traced by maser Zeeman splitting).