Discovery of 14NH3 (2,2) Maser Emission in Sgr B2 Main

We report the discovery of the first 14NH3 (2,2) maser, seen in the Sgr B2 Main star-forming region near the center of the Milky Way, using data from the Very Large Array radio telescope. The maser is seen in both lower-resolution (3″ or ∼0.1 pc) data from 2012 and higher-resolution (0 1 or ∼1000 au) data from 2018. In the higher-resolution data NH3 (2,2) maser emission is detected toward five independent spots. The maser spots are not spatially or kinematically coincident with any other masers in this region, or with the peaks of the radio continuum emission from the numerous ultracompact and hypercompact H ii regions in this area. While the (2,2) maser spots are spatially unresolved in our highest-resolution observations, they have unusually broad line widths of several kilometers per second, which suggests that each of these spots consists of multiple masers tracing unresolved velocity structure. No other NH3 lines observed in Sgr B2 Main are seen to be masers, which continues to challenge existing models of NH3 maser emission.