Letter to the Editor

Discovery of non-metastable ammonia masers in Sagittarius B2

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: yyan@mpifr-bonn.mpg.de, astrotingyan@gmail.com
² Astronomy Department, Faculty of Science, King Abdulaziz University, PO Box 80203, Jeddah 21589, Saudi Arabia
³ Xinjiang Astronomical Observatory, Chinese Academy of Sciences, 830011 Urumqi, PR China
⁴ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475, USA
⁵ Department of Astronomy, University of Florida, PO Box 112055, Florida, USA
⁶ Center for Astrophysics, Guangzhou University, 510006 Guangzhou, PR China

Received: 20 September 2022
Accepted: 23 September 2022

Abstract

We report the discovery of widespread maser emission in non-metastable inversion transitions of NH₃ toward various parts of the Sagittarius B2 molecular cloud and 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 NH₃ (6,3) maser in Sgr B2(NS), and NH₃ (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 the 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 10⁵ K, manifesting the lines’ maser nature. In view of the masers’ velocity differences with respect to adjacent hot molecular cores and/or UCH 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 II regions. Overall, Sgr B2 is unique in that it allows us to measure many NH₃ masers simultaneously, which may be essential in order to elucidate their thus far poorly understood origin and excitation.