| Issue |
A&A
Volume 667, November 2022
|
|
|---|---|---|
| Article Number | A151 | |
| Number of page(s) | 18 | |
| Section | Interstellar and circumstellar matter | |
| DOI | https://doi.org/10.1051/0004-6361/202244631 | |
| Published online | 22 November 2022 | |
CHEMOUT: CHEMical complexity in star-forming regions of the OUTer Galaxy
III. Nitrogen isotopic ratios in the outer Galaxy
1
Centro de Astrobiología (CAB), CSIC-INTA,
Ctra. de Ajalvir Km. 4,
28850
Torrejón de Ardoz, Madrid, Spain
e-mail: lcolzi@cab.inta-csic.es
2
INAF – Osservatorio di Astrofísica e Scienza dello Spazio,
Via Gobetti 93/3,
40129
Bologna, Italy
3
INAF – Osservatorio Astrofísico di Arcetri,
Largo E. Fermi 5,
50125
Florence, Italy
4
Department of Chemistry “Giacomo Ciamician”, University of Bologna,
Via F. Selmi 2,
Bologna
40126, Italy
5
Centre for Astrochemical Studies, Max-Planck-Institute for Extraterrestrial Physics,
Giessenbachstrasse 1,
85748
Garching, Germany
6
INAF – IAPS,
via Fosso del Cavaliere, 100,
00133
Roma, Italy
Received:
29
July
2022
Accepted:
16
September
2022
Context. Nitrogen isotopic ratios are a key tool for tracing Galactic stellar nucleosynthesis.
Aims. We present the first study of the 14N/15N abundance ratio in the outer regions of the Milky Way (namely, for galactocentric distances, RGC, from 12 up to 19 kpc), with the aim to study the stellar nucleosynthesis effects in the global Galactic trend.
Methods. We analysed IRAM 30 m observations towards a sample of 35 sources in the context of the CHEMical complexity in star-forming regions of the OUTer Galaxy (CHEMOUT) project. We derived the 14N/15N ratios from HCN and HNC for 14 and 3 sources, respectively, using the J = 1–0 rotational transition of HN13C, H15NC, H13CN, and HC15N.
Results. The results found in the outer Galaxy have been combined with previous measurements obtained in the inner Galaxy. We find an overall linear decreasing H13CN/HC15N ratio with increasing RGC. This translates to a parabolic 14N/15N ratio with a peak at 11 kpc. Updated Galactic chemical evolution models have been taken into account and compared with the observations. The parabolic trend of the 14N/15N ratio with RGC can be naturally explained (i) by a model that assumes novae as the main 15N producers on long timescales (≥1 Gyr) and (ii) by updated stellar yields for low- and intermediate-mass stars.
Key words: Galaxy: abundances / Galaxy: evolution / local insterstellar matter / ISM: abundances / ISM: molecules / radio lines: ISM
© L. Colzi et al. 2022
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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