A Centimeter-wave Study of Methanol and Ammonia Isotopologues in Sgr
  B2(N): Physical and chemical differentiation between two hot cores
  We present new radio-frequency interferometric maps of emission from the
14NH3, 15NH3, and 14NH2D 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 HII regions in this area. The
first (N1) is the well-known v = 64 km/s core, and the second (N2) is a core
6'' to the north at v = 73 km/s. 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 14NH2D. We find that
the ammonia deuteration fraction of N2 is roughly 10-20 times higher than in
N1. We also measure an [15NH3/14NH3] abundance ratio that is apparently 2-3
times higher in N2 than 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.
