2018ApJ...869..121M

We present new radio-frequency interferometric maps of emission from the ¹⁴NH₃, ¹⁵NH₃, and NH₂D isotopologues of ammonia and the ¹²CH₃OH and ¹³CH₃OH isotopologues of methanol toward Sgr B2(N). With a resolution of ∼3'' (0.1 pc), we are able to spatially resolve emission from two hot cores in this source and separate it from absorption against the compact H II regions in this area. The first (N1) is the well-known v = 64 km s^–1 core, and the second (N2) is a core 6'' to the north at v = 73 km s^–1. Using emission from ¹⁵NH₃ and hyperfine satellites of ¹⁴NH₃ metastable transitions, we estimate the ¹⁴NH₃ column densities of these sources and compare them to those of NH₂D. We find that the ammonia deuteration fraction of N2 is roughly 10-20 times higher than that in N1. We also measure an [¹⁵NH₃/¹⁴NH₃] abundance ratio that is apparently 2-3 times higher in N2 than in N1, which could indicate a correspondingly higher degree of nitrogen fractionation in N2. In addition, we find that N2 has a factor of 7 higher methanol abundance than N1. Together, these abundance signatures suggest that N2 is a younger source, for which species characteristic of grain chemistry at low temperatures are currently being actively liberated from ice mantles and have not yet reached chemical equilibrium in the warm gas phase. The high D abundance and possible high ¹⁵N abundance in NH₃ found in N2 are interesting for studying the potential interstellar origin of abundances in primitive solar system material.