New Maser Emission from Nonmetastable Ammonia in NGC 7538. II. Green Bank Telescope Observations Including Water Masers

TL;DR

This study reports new ammonia and water maser emissions in NGC 7538, revealing stable ammonia masers over two months and the highest velocity water masers observed, with implications for the region's stellar evolution.

Contribution

It provides the first detection of non-variable ammonia masers in NGC 7538 and characterizes high-velocity water masers, expanding understanding of maser phenomena in star-forming regions.

Findings

Ammonia masers show no variability over two months.

Water masers exhibit the highest velocities observed in NGC 7538.

No correlation between water and ammonia maser emissions.

Abstract

We present new maser emission from ^{14}NH_3 (9,6) in NGC 7538. Our observations include the known spectral features near v_LSR = -60 km/s and -57 km/s and several more features extending to -46 km/s. In three epochs of observation spanning two months we do not detect any variability in the ammonia masers, in contrast to the >10-fold variability observed in other ^{14}NH_3 (9,6) masers in the Galaxy over comparable timescales. We also present observations of water masers in all three epochs for which emission is observed over the velocity range -105 km/s < v_LSR < -4 km/s, including the highest velocity water emission yet observed from NGC 7538. Of the remarkable number of maser species in IRS 1, H_2O and, now, ^{14}NH_3 are the only masers known to exhibit emission outside of the velocity range -62 km/s < v_LSR < -51 km/s. However, we find no significant intensity or velocity correlations between the water emission and ammonia emission. We also present a non-detection in the most sensitive search to date toward any source for emission from the CC^{32}S and CC^{34}S molecules, indicating an age greater than \approx 10^4 yr for IRS 1-3. We discuss these findings in the context of embedded stellar cores and recent models of the region.