The sulphur depletion problem in molecular clouds: The H₂S case

Abstract

Sulphur is one of the most abundant elements in the Universe and plays a crucial role in biological systems. However, sulphuretted molecules in the ISM are not as abundant as expected and there is no clear answer of where the missing Sulphur is yet. To shed light onto this open question, we focus our attention on the chemistry of H2S, thought to be an important reservoir of Sulphur and formed mainly by grain-phase reactions. To understand the formation of H2S, the growth of ices, and the chemical desorption process, we study the CO, CH3OH, N2H+, and H2S abundances towards Barnard 1b, a Sulphur-rich cloud hosting a first Larson core. We look for correlations between gas-phase abundances of H2S and CH3OH that better constrain the location of the CO snowline in dark cores. Finally, this provides additional data to benchmark models for a deeper insight on the chemical desorption process and its efficiency.