Viti, S., Fontani, F., Jiménez Serra, I., Holdship, J. 2019. Nitrogen fractionation in external galaxies. Monthly Notices of the Royal Astronomical Society 486, 4, 4805-4812 DOI: 10.1093/mnras/stz1172
In star-forming regions in our own Galaxy, the N-14/N-15 ratio is found to vary from similar to 100 in meteorites, comets, and proloplanelary discs up to similar to 1000 in pre-stellar and star-forming cores, while in external galaxies the very few single-dish large-scale measurements of this ratio lead to values of 100-450. The extent of the contribution of isotopic fractionation to these variations is, to date, unknown. In this paper, we present a theoretical chemical study of nitrogen fractionation in external galaxies in order to determine the physical conditions that may lead to a spread of the N-14/N-15 ratio from the solar value of similar to 440 and hence evaluate the contribution of chemical reactions in the interstellar medium (ISM) to nitrogen fractionation. We rind that the main cause of ISM enrichment of nitrogen fractionation is high gas densities, aided by high fluxes of cosmic rays.