Sulfur-Bearing Molecules In Massive Star-Forming Regions: Observations Of OCS, CS, H2S and SO

TL;DR

This study investigates sulfur-bearing molecules in massive star-forming regions using submillimeter spectroscopy, revealing their abundance variations and potential as chemical clocks for star formation stages.

Contribution

It provides new observational data on sulfur molecule abundances and suggests their ratios can serve as chemical clocks in massive star-forming regions.

Findings

H2S is likely the most abundant sulfur molecule in hot cores.

Sulfur molecule abundances decrease from hot core to H II-only sources.

Abundance ratios can indicate evolutionary stages of star-forming regions.

Abstract

We studied sulfur chemistry of massive star-forming regions through single-dish submillimeter spectroscopy. OCS, O13CS, 13CS, H2S and SO transitions were observed toward a sample of massive star-forming regions with embedded UCH II or CH II regions. These sources could be divided into H II-hot core and H II-only sources based on their CH3CN emission. Our results show that the OCS line of thirteen sources is optically thick, with optical depth ranging from 5 to 16. Column densities of these molecules were computed under LTE conditions. CS column densities were also derived using its optically thin isotopologue 13CS. H2S is likely to be the most abundant gas-phase sulfuretted molecules in hot assive cores. Both the column density and abundance of sulfur-bearing molecules decrease significantly from H II-hot core to H II-only sources. Ages derived from hot core models appear to be consistent with star-formation theories, suggesting that abundance ratios of [CS]/[SO], [SO]/[OCS] and [OCS]/[CS] could be used as chemical clocks in massive star-forming regions.