Discovery of widespread non-metastable ammonia masers in the Milky Way

• Published in: Astronomy and astrophysics (Berlin) 2024-06, Vol.686, p.A205
• Main Authors: Yan, Y. T., Henkel, C., Menten, K. M., Wilson, T. L., Wootten, A., Gong, Y., Wyrowski, F., Yang, W., Brunthaler, A., Kraus, A., Winkel, B.
• Format: Article
• Language: English
• Subjects: Ammonia; Emission; Energy levels; Masers; Massive stars; Milky Way; Star formation
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361/202348931

We present the results of a search for ammonia maser emission in 119 Galactic high-mass star-forming regions (HMSFRs) known to host 22 GHz H 2 O maser emission. Our survey has led to the discovery ofnon-metastable NH 3 inversion line masers toward 14 of these sources. This doubles the number of known non-metastable ammonia masers in our Galaxy, including nine new very high-excitation ( J , K ) = (9,6) maser sources. These maser lines, including NH 3 (5,4), (6,4), (6,5), (7,6), (8,6), (9,6), (9,8), (10,8), and (11,9), arise from energy levels of 342 K, 513 K, 465 K, 606 K, 834 K, 1090 K, 942 K, 1226 K, and 1449 K above the ground state. Additionally, we tentatively report a new metastable NH 3 (3,3) maser in G048.49 and an NH 3 (7,7) maser in G029.95. Our observations reveal that all of the newly detected NH 3 maser lines exhibit either blueshifted or redshifted velocities with respect to the source systemic velocities. Among the non-metastable ammonia maser lines, larger velocity distributions, offset from the source systemic velocities, are found in the ortho-NH 3 ( K = 3 n ) transitions than in the para-NH 3 ( K ≠ 3 n ) ones.