Discovery of non-metastable ammonia masers in Sagittarius B2

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 UCHII 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 UCHII 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.

Maser Activity of Organic Molecules toward Sgr B2(N)

“…We also constrain the n H 2 of the masing clumps to be (5-8) × 10 4 cm −3 , a level significantly lower than that derived for (Argon et al 2000;Caswell et al 2010;Walsh et al 2014;Yan et al 2022). The K4 core and arc-like K6 H II region are marked with a green circle marker and dotted line, respectively.…”

“…Six OH maser spots have been identified with a VLA survey of OH masers, with the brightest spot being associated with the K3 centimeter-wave core (Argon et al 2000;Qiao et al 2014). In a recent VLA observation, nine NH 3 (9, 6) maser spots were resolved in this region; most of these spots are concentrated in the N1-K2-K3 region, while the brightest spot is located toward the N3 hot molecular core (Yan et al 2022). In contrast, the maser emission of the organic molecular species presented in this work is found to be located close to the K4 centimeter-wave core and the K6 H II region, being spatially offset from the spots of the radiative pumping maser species OH and Class II CH 3 OH.…”

“…Yellow shading indicates the overlap region where the CH 3 OH emission exceeds 40σ and the CH 2 NH emission exceeds 4σ. The 84 GHz Class I CH 3 OH maser spots, MS1 and MS2, are marked with + symbols in magenta, while the brightest maser spots of OH, H 2 O, NH 3 , and Class II CH 3 OH masers are marked in other colors(Argon et al 2000;Caswell et al 2010;Walsh et al 2014;Yan et al 2022). The K4 core and arc-like K6 H II region are marked with a green circle marker and dotted line, respectively.…”

Maser Activity of Large Molecules toward Sgr B2 North

“…The 83-km s −1 components of the 84 GHz Class I CH3OH maser, 5.29 GHz CH2NH maser, and 4.36 GHz CH2NH2 maser are shown with contours and superimposed on the free-free continuum emission at 6.8 cm. The brightest 84 GHz Class I CH3OH maser spot is marked with a diamond symbol while the brightest maser spots of OH, H2O, NH3, and Class II CH3OH masers are marked with + symbols(Argon et al 2000;Caswell et al 2010;Walsh et al 2014;Yan et al 2022). The arc-like K6 H II region is marked with a yellow dotted line.…”