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