Shocks & Ice Chemistry

Many of the most complex molecules in the interstellar medium are believed to be produced within the ice mantles on dust grains. However, this chemical reservoir is notoriously difficult to constrain due to being invisible to astrochemist's favorite radio telescopes and existing limitations of infrared ice absorption techniques. Instead, we must rely of theoretical models and laboratory experiments to infer what likely is occurring in interstellar ice. However, one way to work around this barrier is to study astrophysical shocks, where the rich solid-phase chemistry is temporarily lifted into the gas-phase. I am particularly interesting in studying these such shocks produced by protostellar outflows, or where a newborn star's burps collide with its stellar nursery. (Banner image by Martina Pepiciello)

Modeling C-Shock Chemistry

Using advanced chemical models that simulate both gas and ice chemistry, I have worked to simulate how molecules will evolve throughout a shock. In particular, I determined some molecules are good tracers of their initial ice abundance while others undergo significant post-shock chemistry that is perhaps even time-dependent (Burkhardt et al. 2019). These predictions can be tested against astronomical observations. Going forward, I am developing a more advanced version of the model to include additional processes, such as cosmic ray chemistry.

Chemically-Active Outflows

Using interferometers and single-dish telescopes, I study how the chemistry in shocked outflows evolves over time and physical conditions. "Chemically-active" outflows, known for their molecule-rich shock events, are ideal for these studies, but are unfortunately rare. In a study of L1157, I constrained the underlying chemistry of CH3OH, HCN, HCO+, and HNCO through a comparison of their morphology and abundances (Burkhardt et al. 2016). Currently, I am undergoing several chemical surveys of chemically-active outflows with interferometers such as the SMA and ALMA, including L1157, IRAS 20126, and HH114, as well as hunting for new ones.

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