Local Constraints On Alcohol–Thioalcohol Analogs In G35.2N

[astro-ph.GA] The chemistry of sulfur-bearing complex organic molecules in dense star-forming environments remains uncertain, partly because the dominant sulfur reservoirs in dense gas and ices are poorly identified. Alcohol–thioalcohol pairs allow direct comparisons of structurally related O- and S-bearing molecules.

We present ALMA Band 6 observations of CH₃OH/CH₃SH and C₂H₅OH/C2H₅SH toward three spectral-extraction positions (MM3-pos, MM4-pos, and MM5-pos) in the MM3–MM5 region of G35.2N. Local thermodynamic equilibrium modeling yields column densities and abundance ratios. CH₃OH column densities were inferred from ¹³CH₃OH assuming ¹²C/¹³C = 50 to mitigate optical-depth effects.

CH₃OH, CH₃SH, and C₂H₅OH are robustly constrained at all three positions; C₂H₅SH is robustly constrained at MM3-pos and MM5-pos but remains tentative at MM4-pos. The corresponding adopted column-density ranges are (1.8−2.7)×10¹⁸, (1.7−2.6)×10¹⁶, (5.7−8.5)×10¹⁶, and (2.4−4.6)×10¹⁵ cm⁻². The CH₃OH/C₂H₅OH and CH₃OH/CH₃SH ratios are consistent across the positions within uncertainties, with nominal values of 31–32 and 100–110, respectively.

Comparisons with chemically rich sources and warm-up chemical models show that CH₃OH/C₂H₅OH lies within the range measured elsewhere, whereas CH₃OH/CH₃SH exhibits greater source-to-source variation. The ethyl-level O/S comparison remains less certain because many literature C₂H₅SH measurements provide only lower limits.

CH₃OH/CH₃SH is thus the best-constrained O/S alcohol–thioalcohol ratio in these data and provides an empirical probe of source-dependent sulfur-bearing organic chemistry. More sensitive C₂H₅SH observations are needed to test C₂H₅OH/C₂H₅SH.

Xuefang Xu, Shanghuo Li, Qian Gou, Chunguo Duan, Laurent Pagani, Di Li, Jun Kang, Jiaxin Du, Jiaxiang Jiao

Comments: 8 pages, 9 figures, 6 tables, published in A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2609.20671 [astro-ph.GA] (or arXiv:2609.20671v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2609.20671
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Journal reference: Astronomy & Astrophysics, 2026, Volume 713, Number 67
Related DOI:
https://doi.org/10.1051/0004-6361/202661403
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Submission history
From: Xuefang Xu
[v1] Thu, 17 Sep 2026 16:46:39 UTC (7,657 KB)
https://arxiv.org/abs/2609.20671

Astrobiology, Astrochemistry,