It is well known that the 14N/15N isotopic ratio found for the proto-Solar nebula (PSN), 440, is significantly higher than that measured in pristine Solar System materials, like comets (~140) and carbonaceous chondrites (~50-250). This suggests a local chemical enrichment of 15N during the Sun formation process. However, the cause of this enrichment and its relation with the natal clump are still uncertain. Since there is growing evidence pointing out that our Sun was born in a rich cluster containing massive stars, we have studied the 14N/15N ratio in a large sample of high-mass star forming regions. In this talk I will first show the overall behaviour of the 14N/15N ratio across the Galaxy. We have confirmed, based on a solid statistics for the first time, that the 14N/15N ratio increases with the Galactocentric distance as a consequence of the Galactic chemical evolution. Moreover, we have estimated that the 14N/15N ratio in the local interstellar medium is about 400, i.e. very close to the PSN value. Then, I will zoom-in into the massive star-forming protocluster IRAS 05358+3543, where we have obtained the first interferometric maps of N-fractionation combining single-dish and high-resolution interferometric observations of the 15N isotopologues of N2H+ (see Fig. in attachment). The analysis yields 14N/15N ratios of 100-200 in the cores, and higher values higher than 200 in the diffuse clump gas. This result, which strongly suggests a local chemical enrichment of 15N at core-scales, helps us to understand how the chemical inventory evolves from the parental molecular reservoir to smaller-scale objects, in which star-formation occurs. It suggests also that the 15N-enrichment measured in the pristine Solar System material could occur locally, in the environment in which the Sun was born, during the protocluster evolution.

Enhanced nitrogen fractionation at core scales: High-mass star-forming region IRAS 05358+3543

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.