Shock-enhanced ammonia emission in the Egg nebula

TL;DR

This study uses high-resolution observations to reveal shock-enhanced ammonia emission in the Egg Nebula, showing how high-velocity outflows interact with surrounding gas, leading to increased ammonia abundance.

Contribution

It provides detailed spatial and kinematic analysis of ammonia emission, demonstrating shock-induced ammonia enhancement in a proto-planetary nebula.

Findings

Ammonia emission aligns with shock-excited regions.

Higher inversion transitions are stronger in polar regions.

Ammonia abundance is significantly increased by shocks.

Abstract

We present high angular resolution observations of the NH$_3$(1,1), (2,2) and (3,3) inversion transitions from the Egg Nebula, the archetypical proto-planetary nebula. The spatial distribution and kinematics of the emission in all three lines show four distinct components or lobes that are aligned with the polar and equatorial directions. The kinematics of the NH$_3$ emission is also found to follow a clear pattern: redshifted emission in the South and West and blueshifted emission in the North and East. The morphology and spatial kinematics of NH$_3$ emission are shown to have strong similarity to that observed previously in molecular hydrogen emission and CO emission which arise from the shocked molecular gas. We also find that the higher lying inversion transition NH$_3$ (2,2) and (3,3) are stronger in the polar direction in comparison to the lower transition NH$_3$ (1,1). We conclude that the NH$_3$ emission traces the warm molecular gas, which is shocked and heated by the interaction between the high velocity outflows and the surrounding envelope. The presence of strong ammonia emission associated with the shock fronts and the lack of the emission at the center of the nebula indicate that the abundance of ammonia is significantly enhanced by shocks, a situation very similar to that found in outflows from protostars.