Astrochemical modeling with nondiffusive mechanisms and a study of chemical evolution in various star-forming regions
Jin, Mi Wha, Chemistry - Graduate School of Arts and Sciences, University of Virginia
Garrod, Rob, AS-Chemistry, University of Virginia
Our Galaxy is replete with molecules: from simple species such as H2 and CO to more complex organic molecules (COMs)*, a rich chemical diversity has been unveiled in the interstellar medium over the past several decades. Understanding the degree to which chemical complexity can occur during the star formation process and how much of this complexity may be inherited by emerging planetary systems is important to answer our fundamental questions about the origin of life (Jorgensen, Belloche & Garrod, 2020). It has long been highlighted the important role of chemistry taking place on the surfaces of ice mantles** on interstellar dust grains to explain the chemical complexity in space. However the standard scheme of grain surface chemistry relies on thermal / energetic processes, which cannot fully explain the presence of saturated COMs in cold and quiescent environments.
To tackle this problem, we introduced the so-called "nondiffusive" mechanisms into an astrochemical model MAGICKAL. These mechanisms promote the formation of COMs without thermal diffusion of heavy species on the grain surface. Thus it can provide a general means to treat all temperature regimes in a consistent way.
Based on this advanced model, we investigated the chemistry in various star-forming regions from a cold and quiescent star-forming region (L1544) to an active star-forming region (Orion KL). We found that the new mechanisms significantly enhanced COM abundances in cold environments, successfully reproducing key observational results for the two extreme cases of star formation. Besides the investigation of chemistry based on the readily available observational data, we also provide the prediction of the ice composition for a young and deeply embedded protostar (Cha-MMS1) to assess the detectability of new ice species with the upcoming James Webb Space Telescope observations.
* Per common use in astrochemistry: Carbon-bearing molecules containing 6 or more atoms
** The accumulation of ice layers beneath the outer ice surface
PHD (Doctor of Philosophy)