On the reservoir of sulphur in dark clouds: chemistry and elemental abundance reconciled

Abstract

Sulphur-bearing species are often used to probe the physical structure of\nstar forming regions of the interstellar medium, but the chemistry of sulphur\nin these regions is still poorly understood. In dark clouds, sulphur is\nsupposed to be depleted under a form which is still unknown despite numerous\nobservations and chemical modeling studies that have been performed. In order\nto improve the modeling of sulphur chemistry, we propose an enhancement of the\nsulphur chemical network using experimental and theoretical literature. We test\nthe effect of the updated network on the outputs of a three phases gas-grain\nchemical model for dark cloud conditions using different elemental sulphur\nabundances. More particularly, we focus our study on the main sulphur\nreservoirs as well as on the agreement between model predictions and the\nabundances observed in the dark cloud TMC-1 (CP). Our results show that\ndepending on the age of the observed cloud, the reservoir of sulphur could\neither be atomic sulphur in the gas-phase or HS and H2S in icy grain bulks. We\nalso report the first chemical model able to reproduce the abundances of\nobserved S-bearing species in TMC-1 (CP) using as elemental abundance of\nsulphur its cosmic value.\n