Modelling the sulphur chemistry evolution in Orion KL

Abstract

Context. We present a study of the sulphur chemistry evolution in the region Orion KL along the gas and grain phases of the cloud. Aims. Our aim is to investigate the processes that dominate the sulphur chemistry in Orion KL and to determine how physical and chemical parameters, such as the final mass of the star and the initial elemental abundances, influence the evolution of the hot core and of the surrounding outflows and shocked gas (the plateau). Methods. We independently modelled the chemistry evolution of the hot core and the plateau using the time-dependent gas-grain model UCL_CHEM and considering two different phase calculations. Phase I starts with the collapsing cloud and the depletion of atoms and molecules onto grain surfaces. Phase II starts when a central protostar is formed and the evaporation from grains takes place. We show how the stellar mass, the gas density, the gas depletion efficiency, the initial sulphur abundance, the shocked gas temperature, and the different chemical paths on the grains leading to different reservoirs of sulphur on the mantles affect sulphurbearing molecules at different evolutionary stages for both components. We also compare the predicted column densities with those inferred from observations of the species SO, SO 2 , CS, OCS, H 2 S, and H 2 CS.Results. The models that reproduce the observations of the largest number of sulphur-bearing species in both components are those with an initial sulphur abundance of 0.1 times the sulphur solar abundance (0.1 S ) and a density of at least n H = 5 × 10 6 cm −3 in the shocked gas region. Conclusions. We conclude that most of the sulphur atoms were ionised during Phase I, consistent with an inhomogeneous and clumpy region where the UV interstellar radiation penetrates and leading to sulphur ionisation. We also conclude that the main sulphur reservoir on the ice mantles was H 2 S. In addition, we deduce that a chemical transition currently takes place in the plateau shocked gas, where SO and SO 2 gas-phase formation reactions change from being dominated by O 2 to being dominated by OH.

Pore evolution in interstellar ice analogues

“…In this study, we used a heating schema from Garrod & Herbst (2006) to mimic the temperature of the dust around a massive protostar. However, recent studies suggest that the heating schema could be much longer than that considered here (Esplugues et al 2014). In this case, the decrease of surface area would occur at even lower temperatures than shown in Fig.…”

Submillimeter-HCN Diagram for Energy Diagnostics in the Centers of Galaxies

“…Indeed, while N N CS SO in the CNDs of NGC 1097 and NGC 1068 estimated in LTE analysis are ∼2-3 (Martín et al 2015;Nakajima et al 2015), it is just ∼0.2 in the Orion hot core ( Table 2 in Esplugues et al 2014). If we regard the above CNDs as influenced by mechanical heating, and the abundances of these species in NGC 1097 and NGC 1068 depend on the evolution of hot core-like systems, this result indicates that NGC 1097 and NGC 1068 are more evolved systems than the Orion hot core (e.g., Charnley 1997; Esplugues et al 2014). Future sensitive and systematic study of time clock species will help us understand the chemical evolution in AGNs.…”

Sulphur-bearing species in the coma of comet 67P/Churyumov–Gerasimenko

“…3) for collapsing cloud models in which cosmic rays are somewhat enhanced and hydrogenation of the accreting species is less than 50 per cent. This model is a follow-up of Esplugues et al (2014), who investigated the time-dependent sulphur chemistry evolution using a coupled gas-grain model approach starting with the cloud collapse and condensation of species on to grain surfaces followed by sublimation and subsequent chemical reactions during the formation of the central protostar. The main addition of the Woods et al (2015) models is the inclusion of the results of the ice photolysis and radiolysis experiments to form refractory sulphur-bearing species.…”