Deuterated ammonia in Galactic massive star-forming regions

Abstract

ABSTRACT We present sensitive observations of NH2D $1_{11}^\mathrm{ a}\!-\!1_{01}^\mathrm{ s}$ at 110.153 599 GHz toward 50 Galactic massive star-forming regions with the Institut de Radioastronomie Millimétrique (IRAM) 30-m telescope. The NH2D $1_{11}^\mathrm{ a}\!-\!1_{01}^\mathrm{ s}$ transition is detected toward 36 objects, yielding a detection rate of 72 per cent. 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 NH3, defined as the abundance ratio of NH2D to NH3, for 19 sources is also obtained with the NH3 information 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 Galactocentric distance and decreases with line width.