Deuterated ammonia in Galactic massive star-forming regions

TL;DR

This study investigates deuterated ammonia in 50 massive star-forming regions, revealing high deuterium ratios that increase with distance from the Galactic center and decrease with line width, providing insights into star formation chemistry.

Contribution

First comprehensive survey of NH2D in massive star-forming regions, establishing deuterium fractionation patterns and their dependence on galactic environment.

Findings

Detection rate of NH2D is 72%.

Deuterium ratio varies from 0.0006 to 0.043.

Deuterium ratio increases with Galactocentric distance.

Abstract

We present sensitive observations of NH2D at 110.153599 GHz toward 50 Galactic massive star-forming regions with IRAM 30-m telescope. The NH2D transition is detected toward 36 objects, yielding a detection rate of 72%. Column densities of NH2D, HC3N and C18O for each source are derived by assuming local thermal equilibrium conditions with a fixed excitation temperature. The deuterium ratio of NH$_3$, defined as the abundance ratio of NH2D to NH3, for 19 sources is also obtained with the information of NH3 from the literature. The range of deuterium fractionation bends to be large in the late-stage star-forming regions in this work, with the value from 0.043 to 0.0006. The highest deuterium ratio of NH3 is 0.043 in G081.75+00.78 (DR21). We also find that the deuterium ratio of NH3 increases with the Galactocentric distances and decreases with the line width.