The first high-resolution observations of 19.9-GHz methanol masers

TL;DR

This study presents the first high-resolution observations of 19.9-GHz methanol masers, revealing their distinct spatial and velocity characteristics compared to other class II methanol masers, and suggesting an evolutionary phase in star formation.

Contribution

It provides the first high-resolution imaging of 19.9-GHz methanol masers and compares their properties with other transitions, offering new insights into their spatial distribution and evolutionary significance.

Findings

19.9-GHz masers are spatially coincident with 6.7-GHz masers within 0.2 arcseconds.

Peak velocities of 19.9-GHz masers often differ from other class II transitions.

19.9-GHz masers likely trace a specific evolutionary phase in star formation.

Abstract

We have used the Australia Telescope Compact Array to undertake the first high-resolution observations of the 19.9-GHz methanol maser transition. The emission is coincident with the location of the targeted 6.7-GHz methanol masers to within 0.2 arcseconds in absolute position. We find that the relative distribution of the 19.9-GHz maser emission in our sample differs from that observed in the 6.7-GHz transition, in contrast to the similar distribution often seen in the 6.7- and 12.2-GHz methanol masers in many sources. We also find that the peak velocity for the 19.9-GHz methanol masers is frequently different from that observed in other class II transitions in the same regions. These two results suggest that while 19.9-GHz methanol masers arise from the same general location as other class II transitions, they are likely not coincident on milliarcsecond scales; which has implications for multi-transitional modelling of class II methanol maser sources. We have investigated the properties of the OH and other classII methanol transitions for those 107-GHz methanol masers with and without an associated 19.9-GHz methanol maser. On the basis of these comparisons we suggest that the 19.9-GHz transition traces an evolutionary phase around the peak of the class II maser luminosity into its decline.