Expanded Very Large Array Detection of 44.1 GHz Class I Methanol Masers in Sagittarius A

TL;DR

This study reports the detection of 44 GHz Class I methanol masers in Sagittarius A using EVLA, revealing multiple shock tracers and providing insights into the physical conditions and shock front geometry in the region.

Contribution

First detection of 44 GHz methanol masers in SgrA with EVLA, showing their relation to other masers and shock conditions, advancing understanding of the region's physical environment.

Findings

44 GHz masers correlate with 36 GHz masers but less with 1720 MHz OH masers.

Many 44 GHz masers exist in regions too hot and dense for 36 GHz masers.

The geometry of 36 GHz masers may trace the current shock front.

Abstract

We report on the detection of 44 GHz Class I methanol (CH3OH) maser emission in the SgrA complex with the Expanded Very Large Array (EVLA). These EVLA observations show that the SgrA complex harbors at least four different tracers of shocked regions in the radio regime. The 44 GHz masers correlate with the positions and velocities of previously detected 36 GHz CH3OH masers, but less with 1720 MHz OH masers. Our detections agree with theoretical predictions that the densities and temperatures conducive for 1720 MHz OH masers may also produce 36 and 44 GHz CH3OH maser emission. However, many 44 GHz masers do not overlap with 36 GHz methanol masers, suggesting that 44 GHz masers also arise in regions too hot and too dense for 36 GHz masers to form. This agrees with the non-detection of 1720 MHz OH masers in the same area, which are thought to be excited under even cooler and less dense conditions. We speculate that the geometry of the 36 GHz masers outlines the current location of a shock front.