New Maser Emission from Nonmetastable Ammonia in NGC 7538

TL;DR

This paper reports the first interferometric imaging of nonmetastable ammonia masers in NGC 7538, revealing new emission features and their association with IRS 1, advancing understanding of maser excitation in star-forming regions.

Contribution

It provides the first high-resolution images of nonmetastable ammonia masers in NGC 7538 and identifies new maser components near IRS 1.

Findings

Resolved known maser near -60 km/s into multiple components

Detected new maser features near -57 km/s

Confirmed ammonia masers are associated with IRS 1

Abstract

We present the first interferometric observations at 18.5 GHz of IRS 1 in NGC 7538. These observations include images of the nonmetastable ^{14}NH_3 (9,6) masers with a synthesized beam of 2 arcseconds and images of the continuum emission with a synthesized beam of 150 milliarcseconds. Of the maser emission, the previously known feature near v_LSR = -60 km/s is spectrally resolved into at least two components and we observe several new maser emission features near v_LSR = -57 km/s. The new maser emission near -57 km/s lies 250 +/- 90 milliarcseconds northwest of the maser emission near -60 km/s. All of the masers are angularly unresolved indicating brightness temperatures T_B > 2000 K. We are also able to conclusively associate the ammonia masers with the position of IRS 1. The excitation of these rare ammonia masers is discussed in the context of the rich maser environment of IRS 1.