Characterization of methanol as a magnetic field tracer in star-forming regions

TL;DR

This paper develops a theoretical model to analyze methanol's magnetic properties, enabling more accurate magnetic field measurements in star-forming regions and confirming the significance of magnetic fields around protostars.

Contribution

It introduces a detailed quantum model of methanol's hyperfine structure and g-factors, improving magnetic field interpretation in star formation studies.

Findings

Hyperfine structure affects methanol's magnetic response.

Large variation in Landé g-factors alters previous interpretations.

Magnetic fields around protostars are confirmed as dynamically important.

Abstract

Magnetic fields play an important role during star formation. Direct magnetic field strength observations have proven specifically challenging in the extremely dynamic protostellar phase. Because of their occurrence in the densest parts of star forming regions, masers, through polarization observations, are the main source of magnetic field strength and morphology measurements around protostars. Of all maser species, methanol is one of the strongest and most abundant tracers of gas around high-mass protostellar disks and in outflows. However, as experimental determination of the magnetic characteristics of methanol has remained largely unsuccessful, a robust magnetic field strength analysis of these regions could hitherto not be performed. Here we report a quantitative theoretical model of the magnetic properties of methanol, including the complicated hyperfine structure that results from its internal rotation. We show that the large range in values of the Land\'{e} g-factors of the hyperfine components of each maser line lead to conclusions which differ substantially from the current interpretation based on a single effective g-factor. These conclusions are more consistent with other observations and confirm the presence of dynamically important magnetic fields around protostars. Additionally, our calculations show that (non-linear) Zeeman effects must be taken into account to further enhance the accuracy of cosmological electron-to-proton mass ratio determinations using methanol.