Sulfur-bearing molecules are highly reactive in the gas phase of the ISM. However, the form in which most of the sulfur is locked onto interstellar dust grains is unknown. By taking advantage of the short time-scales of shocks in young molecular outflows, one could track back the main form of sulfur in the ices. In this paper, six transitions of H2S and its isotopologues in the L1157-B1 bowshock have been detected using data from the Herschel-CHESS survey and the IRAM-30m ASAI large program. These detections are used to calculate the properties of H2S gas in L1157-B1 through use of a rotation diagram and to explore the possible carriers of sulfur on the grains. The isotopologue detections allow the first calculation of the H2S deuteration fraction in an outflow from a low mass protostar. The fractional abundance of H2S in the region is found to be 6.0×10−7 and the deuteration fraction is 2×10−2. In order to investigate the form of sulfur on the grains, a chemical model is run with four different networks, each with different branching ratios for the freeze out of sulfur bearing species into molecules such as OCS and H2S. It is found that the model best fits the data when at least half of each sulfur bearing species hydrogenates when freezing. We therefore conclude that a significant fraction of sulfur in L1157-B1 is likely to be locked in H2S on the grains.
@article{arxiv.1608.01983,
title = {H2S in the L1157-B1 Bow shock},
author = {Jonathan Holdship and Serena Viti and Izaskun Jimenez-Serra and Bertrand Lefloch and Claudio Codella and Linda Podio and Milena Benedettini and Francesco Fontani and Rafael Bachiller and Mario Tafalla and Cecilia Ceccarelli},
journal= {arXiv preprint arXiv:1608.01983},
year = {2016}
}
Comments
10 Pages, 7 Figures. Accepted for publication in MNRAS