New Maser Emission from Nonmetastable Ammonia in NGC 7538. III. Detection of the (10,6) Transition and a Velocity Gradient

TL;DR

This paper reports the first detection of nonthermal ammonia maser emission at the (10,6) transition in NGC 7538, imaging multiple maser spots with high brightness temperatures and modeling their kinematics as part of a disk or torus structure.

Contribution

It presents the first astronomical detection of the (10,6) ammonia maser line and confirms multiple masers can occur with the same K value, advancing understanding of maser excitation.

Findings

Detected the (10,6) ammonia maser line in NGC 7538.

Imaged multiple maser spots with sizes < 0.1 arcseconds.

Modeled maser positions and velocities as motion in a disk or torus.

Abstract

We present the first astronomical detection of the 14NH3 (J,K) = (10,6) line: nonthermal emission at several velocities in the Galactic star-forming region NGC 7538. Using the VLA we have imaged the (10,6) and (9,6) ammonia masers at several positions within NGC 7538 IRS 1. The individual sources have angular sizes < 0.1 arcseconds corresponding to brightness temperatures T_B > 1E6 K. We apply the pumping model of Brown & Cragg, confirming the conjecture that multiple ortho-ammonia masers can occur with the same value of K. The positions and velocities of the (10,6) and (9,6) masers are modeled as motion in a possible disk or torus and are discussed in the context of recent models of the region.