Expanded VLA Detection of 36.2 GHz Class I Methanol Masers in Sagittarius A

TL;DR

This paper reports the first interferometric detection of 36.2 GHz Class I methanol masers in Sagittarius A using the EVLA, revealing their association with cloud collisions and their distinction from other maser species.

Contribution

First interferometric detection of 36.2 GHz Class I methanol masers with EVLA, demonstrating their role in tracing cloud collisions and star formation regions.

Findings

36 GHz methanol emission is confirmed as maser emission.

36 GHz and 1720 MHz OH masers are not co-spatial.

Methanol masers correlate with NH3 density peaks.

Abstract

We report on the interferometric detection of 36.2 GHz Class I methanol emission with the new 27-40 GHz Ka band receivers available on the Expanded Very Large Array (EVLA). The brightness temperatures of the interferometric 36 GHz detections unambiguously indicate for the first time that the emission is maser emission. The 36 GHz methanol masers are not co-spatial with 1720 MHz OH masers, indicating that the two species trace different shocks. The 36 GHz and 44 GHz methanol masers, which both are collisionally pumped, do not necessarily co-exist and may trace different methanol gas. The methanol masers seem correlated with NH_3(3,3) density peaks. We favor an explanation in which the 36 GHz Class I methanol masers outline regions of cloud-cloud collisions, perhaps just before the onset of the formation of individual massive stars. The transition of the Very Large Array (VLA) to the EVLA is well under way, and these detections demonstrate the bright future of this completely renewed instrument.