Nitrogen fractionation across the Galaxy: Observations of the 14N/15N ratio in a large sample of high-mass star-forming cores

We have measured the 14N/15N ratio in a sample of 27 high-mass star
forming cores, from observations of HCN(1-0) and HNC(1-0) (Colzi et al.
2017a, in press.). The observations were done with the IRAM-30m
Telescope that is a single-dish Radiotelescope and one of the best
existing radio-millimeter telescopes. Surprisingly, we have found values
that are distributed remarkably well around that of the PSN (about 441).
Moreover, these sources were divided into the three main evolutionary
categories of the high-mass star formation process: 11 high-mass
starless cores, 9 high-mass protostellar objects and 7 ultracompact HII
regions. This study shows that the chemical evolution does not seem to
play a role in the fractionation of nitrogen.
Afterwards we have decided to implement the sample by an even larger
sample of this kind of sources (about 90 in total) observed also with
IRAM 30-m. We have computed the 14N/15N ratios from the same molecules
and we have confirmed that these ratios in these high-mass sources, for
these two molecules, are concentrated from about 270 (value measured for
the terrestrial atmosphere) and about 441 (Colzi et al., in prep).
Thanks to the very large sample and the fact that these sources span a
wide range of distances from the Galactic center, we have decided also
to search for a Galactocentric gradient, and this will be the first for
14N/15N with such a robust statistics.