Issue |
A&A
Volume 690, October 2024
|
|
---|---|---|
Article Number | A372 | |
Number of page(s) | 11 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361/202451412 | |
Published online | 29 October 2024 |
A new measurement of the Galactic 12C/13C gradient from sensitive HCO+ absorption observations
1
Institut de Radioastronomie Millimetrique,
300 rue de la Piscine,
38400
Saint-Martin d’Hères,
France
2
Centro de Astrobiología (CAB), CSIC-INTA,
Ctra. de Ajalvir Km. 4,
28850
Torrejón de Ardoz, Madrid,
Spain
3
Shanghai Astronomical Observatory, Chinese Academy of Sciences,
80 Nandan Road,
Shanghai
200030,
China
4
Research Center for Astronomical Computing, Zhejiang Laboratory,
Hangzhou
311100,
China
5
Department of Astronomy, Tsinghua University,
Beijing
100084,
China
6
CAS Key Laboratory of FAST, National Astronomical Observatories, Chinese Academy of Sciences,
Beijing
100101,
China
7
School of Astronomy and Space Science, Nanjing University,
Nanjing
210093,
China
8
Department of Physics, Anhui Normal University,
Wuhu, Anhui
241002,
China
★ Corresponding author; luo@iram.fr
Received:
7
July
2024
Accepted:
17
September
2024
We present a new constraint on the Galactic 12C/13C gradient with sensitive HCO+ absorption observations against strong continuum sources. The new measurements suffer less from beam dilution, optical depths, and chemical fractionation, allowing us to derive the isotopic ratios precisely. The measured 12C/13C ratio in the solar neighborhood (66±5) is consistent with those obtained from CH+. Two measurements toward the GC are 42.2±1.7 and 37.5±6.5. Though the values are a factor of two to three higher than those derived from dense gas tracers (e.g., H2CO, complex organic molecules) toward Sagittarius (Sgr) B2 regions, our results are consistent with the absorption measurements from c-C3H2 toward Sgr B2 (~40) and those from CH+ toward Sgr A* and Sgr B2(N) (>30). We have calculated a new Galactic 12C/13C gradient of (6.4±1.9)RGC/kpc+(25.9±10.5) and found an increasing trend of the 12C/13C gradient obtained from high-density to low-density gas tracers, suggesting that opacity effects and chemical fractionation may have a strong impact on the isotopic ratios observed in high-density regions.
Key words: astrochemistry / ISM: abundances / ISM: clouds / ISM: molecules / galaxy: evolution
© The Authors 2024
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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