Nitrogen hydrides in interstellar gas: Herschel/HIFI observations towards G10.6-0.4 (W31C)

TL;DR

This study uses Herschel/HIFI observations to analyze nitrogen hydrides in interstellar gas towards G10.6-0.4, revealing their abundances and distribution, and providing insights into interstellar nitrogen chemistry.

Contribution

First detailed Herschel/HIFI observations of multiple nitrogen hydrides towards G10.6-0.4, estimating their abundances and discussing implications for interstellar chemistry models.

Findings

Detected NH, NH2, and NH3 in absorption and emission.

Estimated uniform abundances of NH, NH2, and NH3 relative to hydrogen.

Found no detection of NH+ in the observed spectra.

Abstract

The HIFI instrument on board the Herschel Space Observatory has been used to observe interstellar nitrogen hydrides along the sight-line towards G10.6-0.4 in order to improve our understanding of the interstellar chemistry of nitrogen. We report observations of absorption in NH N=1-0, J=2-1 and ortho-NH2 1_1,1-0_0,0. We also observed ortho-NH3 1_0-0_0, and 2_0-1_0, para-NH3 2_1-1_1, and searched unsuccessfully for NH+. All detections show emission and absorption associated directly with the hot-core source itself as well as absorption by foreground material over a wide range of velocities. All spectra show similar, non-saturated, absorption features, which we attribute to diffuse molecular gas. Total column densities over the velocity range 11-54 km/s are estimated. The similar profiles suggest fairly uniform abundances relative to hydrogen, approximately 6*10^-9, 3*10^-9, and 3*10^-9 for NH, NH2, and NH3, respectively. These abundances are discussed with reference to models of gas-phase and surface chemistry.