Local constraints on alcohol--thioalcohol analogs in G35.2N

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

doi:10.1051/0004-6361/202661403

paper

Local constraints on alcohol--thioalcohol analogs in G35.2N

arXiv:2609.20671 · doi:10.1051/0004-6361/202661403

Abstract

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 CH $_{3}$ OH/CH $_{3}$ SH and C $_{2}$ H $_{5}$ OH/C $_{2}$ H $_{5}$ SH 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. CH $_{3}$ OH column densities were inferred from $^{13}$ CH $_{3}$ OH assuming $^{12}$ C/ $^{13}$ C = 50 to mitigate optical-depth effects. CH $_{3}$ OH, CH $_{3}$ SH, and C $_{2}$ H $_{5}$ OH are robustly constrained at all three positions; C $_{2}$ H $_{5}$ SH is robustly constrained at MM3-pos and MM5-pos but remains tentative at MM4-pos. The corresponding adopted column-density ranges are $(1.8 - 2.7) \times 1 0^{18}$ , $(1.7 - 2.6) \times 1 0^{16}$ , $(5.7 - 8.5) \times 1 0^{16}$ , and $(2.4 - 4.6) \times 1 0^{15}$ cm $^{- 2}$ . The CH $_{3}$ OH/C $_{2}$ H $_{5}$ OH and CH $_{3}$ OH/CH $_{3}$ SH 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 CH $_{3}$ OH/C $_{2}$ H $_{5}$ OH lies within the range measured elsewhere, whereas CH $_{3}$ OH/CH $_{3}$ SH exhibits greater source-to-source variation. The ethyl-level O/S comparison remains less certain because many literature C $_{2}$ H $_{5}$ SH measurements provide only lower limits. CH $_{3}$ OH/CH $_{3}$ SH 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 C $_{2}$ H $_{5}$ SH observations are needed to test C $_{2}$ H $_{5}$ OH/C $_{2}$ H $_{5}$ SH.

8 pages, 9 figures, 6 tables, published in A&A