New interstellar masers in nonmetastable ammonia

Abstract

We report the astronomical detections of several ammonia inversion transitions involving nonmetastable levels with energies as high s 1090 K above the ground state. The (J, K) = (9, 6) inversion transition shows maser-like emission in the directions of W51, NGC 7538, W49, and DR 21(OH). The NH3 (6, 3) line exhibits similar characteristics in W51 but is seen in absorption in NGC 7538. These are the first definite detections of ammonia masers in space. The intensities and narrow line widths (0.5-1.5 km s-1) for the emission features are in contrast to the previously detected broad, weak, nonmetastable lines attributed to thermal emission in these sources. Temporal variability appears to be evident in the (9, 6) emission in W49 over a 4 month period. The highly excited (J, K) = (9, 6) and (6, 3) ammonia lines are found in regions containing compact H II regions and strong infrared sources with associated H2O and OH masers; i.e., in regions of active star formation.

Ammonia in the hot core W 51-IRS2: 11 new maser lines and a maser component with a velocity drift

“…High velocity features ( > ∼ 60 km s −1 ) were observed by Madden et al (1986) and in W51-IRS2. The Madden et al (9,6) spectrum from late 1984 or early 1985 shows about half a dozen of narrow spikes between 50 and 62 km s −1 .…”

“…The (6, 3) and (9, 6) lines (Madden et al 1986), the (5, 4), (7,5), and (9, 8) lines (Mauersberger et al 1987), and the (11, 9) line ) were known before this study. However, the nonthermal features in the (6, 2), (5, 3), (7, 4), (8, 5), (6, 6), (7, 6), (8, 6), (7, 7), (9, 7), (10, 7), (9, 9), (10, 9), and (12, 12) transitions are new discoveries in W51-IRS2, with the (12, 12) transition being the most highly excited NH 3 maser line so far detected.…”

“…There is rapid variability in the (9, 6) line (see previous subsection). In the eighties (Madden et al 1986;), (6, 3) emission was seen at 54 km s −1 . The line has switched from one group of maser components to another.…”

“…(J, K) = (3, 3) maser emission was first detected by Wilson et al (1982) toward the star forming region W 33. To date, several NH 3 maser lines have been observed (e.g., Guilloteau et al 1983;Madden et al 1986;Mauersberger et al 1988b;Hofner et al 1994;Kraemer & Jackson 1995;Beuther et al 2007), even including the rare isotopologue 15 NH 3 (Mauersberger et al 1986b;Schilke et al 1991).…”

“…At a distance of 6.1 ± 1.3 kpc (Imai et al 2002) or 5.1 +2.9 −1,4 kpc (Xu et al 2009), 1 pc subtends ∼40 . With a rotational temperature T rot ∼ 300 K, a source averaged column density of N(NH 3 ) ∼ 10 19 cm −2 , and a virial density of n(H 2 ) ∼ 10 7.7 cm −3 , W51-IRS2 is the source with the largest number of detected masing ammonia lines (Madden et al 1986;Mauersberger et al 1987;). Here we focus on such non-thermally excited lines and report results from monitoring observations spanning a A&A 549, A90 (2013) time interval of almost two decades and leading to the detection of a dozen new molecular maser lines.…”