The deuterium fractionation of NH$_3$ in massive star-forming regions

TL;DR

This study investigates the spatial distribution and environmental dependence of NH$_2$D deuterium fractionation in 12 massive star-forming regions, revealing trends with temperature and core evolution.

Contribution

It provides the first detailed spatial analysis of NH$_2$D deuterium fractionation in multiple massive star-forming regions, highlighting its dependence on temperature and core evolution.

Findings

Deuterium fractionation decreases with increasing temperature in most sources.

The highest deuterium fractionation regions are offset from NH$_3$ peaks.

The correlation between deuterium fractionation and temperature is less significant across all sources.

Abstract

Deuteration is sensitive to environmental conditions in star-forming regions. To investigate NH$_2$D chemistry, we compared the spatial distribution of ortho-NH$_2$D $1_{11}^s-1_{01}^a$, NH$_3$(1,1) and NH$_3$(2,2) in 12 late-stage massive star-forming regions. By averaging several pixels along the spatial slices of ortho-NH$_2$D $1_{11}^s-1_{01}^a$, we obtained the deuterium fractionation of NH$_3$. In seven targets, the deuterium fractionation of NH$_3$ shows a decreasing trend with increasing rotational temperature. This trend is less clear in the remaining five sources, likely due to limited spatial resolution. However, when considering all 12 sources together, the anticorrelation between NH$_3$ deuterium fractionation and rotational temperature becomes less significant, suggesting that other physical parameters may influence the fractionation. Additionally, we found that the region of highest deuterium fractionation of NH$_3$ is offset from the NH$_3$ peak in each source, likely because the temperature is higher near the NH$_3$ peaks and NH$_2$D may be depleted from the gas phase as the molecular cloud core evolves, as well as the increased release of CO from grains into the gas phase.