Seminar by Julia Santos, Leiden University
The observable sulfur content in dense interstellar clouds and protostellar environments corresponds to only a small fraction of the expected cosmic value, with the bulk of its reservoir remaining currently unknown. One hypothesis is that the missing sulfur is locked away in or beneath the icy mantles that shroud interstellar dust grains, challenging its observation. This conspicuous characteristic unique to sulfur-bearing species makes them prominent puzzle pieces in understanding the evolution of volatile and refractory components throughout the different stages of star formation. Sulfur dioxide (SO2) and carbonyl sulfide (OCS) are particularly relevant since both are major carriers of gaseous sulfur and are the only sulfurated molecules detected in interstellar ices to date. Hydrogen sulfide (H2S) is another riveting case, whose efficient predicted formation on interstellar dust grains contrasts with its observationally constrained upper limits. In this seminar, I will showcase laboratory experiments on interstellar ice analogues that allow us to explore potential formation and destruction routes for sulfurated species. They offer particularly promising new pathways to OCS in interstellar ices, as well as direct quantification of H2S destruction mechanisms. I will also present recent results on ALMA observations of gaseous SO2 and OCS towards protostars in comparison to ice counterparts obtained with infrared observatories—including JWST. Such comparisons provide powerful information on the chemical and physical environments of these molecules. Combined, our experimental and observational results contribute to elucidating the still elusive origin and fate of sulfur-bearing molecules in star-forming regions.
Host: Jane Huang