# Nitrogen Fractionation in External Galaxies

## TL;DR

This paper investigates nitrogen isotope ratios in external galaxies through chemical modeling, identifying high gas densities and cosmic rays as key factors influencing nitrogen fractionation variations.

## Contribution

It provides a theoretical analysis of nitrogen fractionation in external galaxies, highlighting physical conditions affecting isotope ratio variations.

## Key findings

- High gas densities promote nitrogen fractionation.
- Cosmic rays significantly influence isotope ratios.
- Variations can reach from solar-like to more enriched values.

## Abstract

In star forming regions in our own Galaxy, the 14N/15N ratio is found to vary from $\sim$ 100 in meteorites, comets and protoplanetary disks up to $\sim$ 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 14N/15N ratio from the solar value of $\sim$440 and hence evaluate the contribution of chemical reactions in the ISM to nitrogen fractionation. We find that the main cause of ISM enrichment of nitrogen fractionation is high gas densities, aided by high fluxes of cosmic rays.