Detection of CH3SH in protostar IRAS 16293-2422

TL;DR

This study reports the detection of the sulphur-bearing molecule CH3SH in the protostar IRAS 16293-2422, providing insights into sulphur chemistry in star-forming regions and suggesting the presence of other undetected S-bearing molecules.

Contribution

First detection of CH3SH in IRAS 16293-2422, linking observations with chemical models to understand sulphur chemistry in star-forming environments.

Findings

CH3SH detected in IRAS 16293-2422

CH3SH abundance is about 4e-9 relative to H2

CH3SH likely formed on grain surfaces

Abstract

The nature of the main sulphur reservoir in star forming regions is a long standing mystery. The observed abundance of sulphur-bearing species in dense clouds is only about 0.1 per cent of the same quantity in diffuse clouds. Therefore, the main sulphur species in star forming regions of the interstellar medium are still unknown. IRAS 16293-2422 is one of the regions where production of S-bearing species is favourable due to its conditions which allows the evaporation of ice mantles. We carried out observations in the 3 mm band towards the solar type protostar IRAS 16293-2422 with the IRAM 30m telescope. We observed a single frequency setup with the EMIR heterodyne 3 mm receiver with an Lower Inner (LI) tuning frequency of 89.98 GHz. Several lines of the complex sulphur species CH3SH were detected. Observed abundances are compared with simulations using the NAUTILUS gas-grain chemical model. Modelling results suggest that CH3SH has the constant abundance of 4e-9 (compared to H2) for radii lower than 200 AU and is mostly formed on the surfaces. Detection of CH3SH indicates that there may be several new families of S-bearing molecules (which could form starting from CH3SH) which have not been detected or looked for yet.