Published in

Oxford University Press (OUP), Monthly Notices of the Royal Astronomical Society, 1(494), p. 1095-1113, 2020

DOI: 10.1093/mnras/staa676

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Isotopologues of dense gas tracers in nearby infrared bright galaxies

Journal article published in 2020 by Fei Li, Junzhi Wang ORCID, Min Fang, Shanghuo Li, Zhi-Yu Zhang ORCID, Yu Gao, Minzhi Kong
This paper was not found in any repository, but could be made available legally by the author.
This paper was not found in any repository, but could be made available legally by the author.

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Data provided by SHERPA/RoMEO

Abstract

ABSTRACT We present 1 and 3 mm observations of the 13C- and 15N-bearing isotopologues of dense gas tracers towards eight nearby infrared-bright galaxies. With the Institut de Radioastronomie Millimétrique 30-m telescope, we observed the J = 1–0 transitions of H13CN, HC15N, H13CO+, HN13C, and H15NC towards M 82, NGC 3079, IC 694, Mrk 231, and NGC 6240. The J = 3–2 transition of H13CN was obtained in M 82, NGC 3079, NGC 3504, NGC 4418, NGC 6240, and NGC 6946, using the 10-m Submillimeter Telescope (SMT). We report the first detections of HN13C J = 1–0 and H13CN J = 3–2 in M 82, and H13CN J = 3–2 in NGC 6240 and NGC 3079. We find different line profiles between the J = 1–0 and 3–2 transitions of H13CN in both M 82 and NGC 3079. The optical depths of HCN show significant variations among the sample, indicating that dense gas masses estimated from the line luminosities of HCN J = 1–0 and 3–2 should be treated with caution for individual galaxies. Optical depth of HCN J = 3–2 is found to be higher than that of HCN J = 1–0 in M 82, NGC 3079, NGC 4418, and NGC 6240, which indicates that ground state transitions of dense gas tracers might better trace the star-forming gas than the high-J transitions. Based on the H13CN/HC15N line ratios, with the double-isotopic method, low 14N/15N abundance ratios of 120 and 140 are found in NGC 3079 and Mrk 231, respectively.

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