Discovery of non-metastable ammonia masers in Sagittarius B2

TL;DR

This paper reports the discovery of widespread non-metastable ammonia masers in Sagittarius B2, revealing new insights into their excitation mechanisms and association with shocks in a complex star-forming region.

Contribution

It presents the first detection of multiple non-metastable ammonia masers in Sagittarius B2, with high-resolution imaging identifying their spatial distribution and physical properties.

Findings

Detected 18 ammonia maser spots across different Sgr B2 regions.

Maser brightness temperatures exceed 3000 K, confirming their maser nature.

Maser velocities suggest association with shocks from outflows or expanding HII regions.

Abstract

We report the discovery of widespread maser emission in non-metastable inversion transitions of NH$_3$ toward various parts of the Sagittarius B2 molecular cloud/star forming region complex: We detect masers in the $J,K = $ (6,3), (7,4), (8,5), (9,6), and (10,7) transitions toward Sgr B2(M) and Sgr B2(N), an NH$_3$ (6,3) maser in Sgr B2(NS), and NH$_3$ (7,4), (9,6), and (10,7) masers in Sgr B2(S). With the high angular resolution data of the Karl G. Jansky Very Large Array (JVLA) in A-configuration we identify 18 maser spots. Nine maser spots arise from Sgr B2(N), one from Sgr B2(NS), five from Sgr B2(M), and three in Sgr B2(S). Compared to our Effelsberg single dish data, the JVLA data indicate no missing flux. The detected maser spots are not resolved by our JVLA observations. Lower limits to the brightness temperature are $>$3000~K and reach up to several 10$^5$~K, manifesting the lines' maser nature. In view of the masers' velocity differences with respect to adjacent hot molecular cores and/or UCH{\scriptsize II} regions, it is argued that all the measured ammonia maser lines may be associated with shocks caused either by outflows or by the expansion of UCH{\scriptsize II} regions. Overall, Sgr B2 is unique in that it allows us to measure many NH$_3$ masers simultaneously, which may be essential to elucidate their so far poorly understood origin and excitation.