A Multitransition Methanol Survey toward a Large Sample of High-mass Star-forming Regions

• Published in: The Astrophysical journal. Supplement series Vol. 266; no. 2; pp. 29 - 45
• Main Authors: Zhao, J. Y., Zhang, J. S., Wang, Y. X., Qiu, J. J., Yan, Y. T., Yu, H. Z., Chen, J. L., Zou, Y. P.
• Format: Journal Article
• Language: English
• Published: Saskatoon The American Astronomical Society 01.06.2023; IOP Publishing
• Subjects: Astrochemistry; Density ratio; Emission analysis; Emission lines; Interstellar molecules; Line spectra; Low temperature; Low temperature environments; Masers; Massive stars; Molecule formation; Rotational temperatures; Star formation; Target detection
• ISSN: 0067-0049; 1538-4365
• DOI: 10.3847/1538-4365/acc323

We carried out a spectral line survey of CH 3 OH toward a large sample of 175 high-mass star-forming regions in the 3 mm, 2 mm, and 1.3 mm bands with the Institut de Radioastronomie Millimétrique (IRAM) 30 m telescope. Out of our 175 targets, 148 sources were detected with one or more CH 3 OH transition lines. Nineteen CH 3 OH transition lines, including 13 thermal lines and 6 maser lines, were detected. The 8 0 → 7 1 A + (∼95.169 GHz) CH 3 OH maser line, one of the strongest class I CH 3 OH maser lines, was detected in 52 sources. Forty-two of them are previously reported masers and the other 10 are new detections. Through analyzing the rotational diagram of the detected CH 3 OH emission lines (nonmasing lines), we obtained the rotational temperature and the column density for 111 sources. Our results show that E -type CH 3 OH tends to have lower column density than A -type CH 3 OH. The column density ratio of E / A was derived in 55 sources with the majority having a ratio less than 1.0 (about 70%), with a peak ratio of ∼0.6. This is consistent with theoretical predictions, i.e., overabundance of A -type CH 3 OH at low temperature leading to a low E / A ratio. Furthermore, we found that CH 3 OH abundance decreases beyond T dust ∼ 30 K, which is supported by modeling results. All these support the fact that CH 3 OH is easily formed at low-temperature environments, via successive hydrogenation of CO on cold dust surfaces.