Testing the Hypothesis that Methanol Maser Rings Trace Circumstellar Disks: High Resolution Near-IR and Mid-IR Imaging

TL;DR

This study used high-resolution near- and mid-infrared imaging to test if methanol maser rings trace circumstellar disks around forming high-mass stars, finding no strong evidence supporting this hypothesis.

Contribution

It provides the first high-resolution infrared imaging comparison to test the disk hypothesis for methanol maser rings around massive young stars.

Findings

Infrared emission geometries do not support the disk hypothesis.

SED modeling results are inconsistent with maser rings tracing disks.

High-resolution imaging challenges previous assumptions about maser ring origins.

Abstract

Milliarcsecond VLBI maps of regions containing 6.7 GHz methanol maser emission have lead to the recent discovery of ring-like distributions of maser spots and the plausible hypothesis that they may be tracing circumstellar disks around forming high mass stars. We aimed to test this hypothesis by imaging these regions in the near and mid-infrared at high spatial resolution and compare the observed emission to the expected infrared morphologies as inferred from the geometries of the maser rings. In the near infrared we used the Gemini North adaptive optics system of Altair/NIRI, while in the mid-infrared we used the combination of the Gemini South instrument T-ReCS and super-resolution techniques. Resultant images had a resolution of approximately 150 mas in both the near-infrared and mid-infrared. We discuss the expected distribution of circumstellar material around young and massive accreting (proto)stars and what infrared emission geometries would be expected for the different maser ring orientations under the assumption that the masers are coming from within circumstellar disks. Based upon the observed infrared emission geometries for the four targets in our sample and the results of SED modeling of the massive young stellar objects associated with the maser rings, we do not find compelling evidence in support of the hypothesis that methanol masers rings reside in circumstellar disks.