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Abstract
Context
Cold dense cores are unique among the structures found in the interstellar medium, as they harbor a rich chemical inventory, including complex organic molecules (COMs), which will be inherited by future evolutionary stages, such as protostellar envelopes and protoplanetary disks. These molecules exist both in the gas phase and as ices accreted onto grain surfaces.
Aims
To model these environments, we present Pegasis, a new, fast, and extensible three-phase astrochemical code to explore the chemistry of cold cores, with an emphasis on the role of diffusive and non-diffusive chemistry in shaping their gas and grain chemical compositions.
Methods
We incorporate the latest developments in interstellar chemistry modeling by utilizing the 2024 KIDA chemical network and comparing our results with current state-of-the-art astrochemical models. Using a traditional rate-equation-based approach, we implement both diffusive and non-diffusive chemistry, coupled with either an inert or chemically active ice mantle.
Results
We identify crucial reactions that enhance the production of COMs through non-diffusive mechanisms on the grain-surface as well as the mechanisms through which they can build up in gas-phase. Across all models with non-diffusive chemistry, we observe a definite enhancement in the concentration of COMs on both grain-surface as well in the grain-mantle. Finally, our model broadly reproduces the observed abundances of multiple gas-phase species in a cold dense core TMC-1 (CP) and provides insights into its chemical age.
Conclusions
Our work demonstrates the capabilities of Pegasis in exploring a wide range of grain-surface chemical processes and modeling approaches for three-phase chemistry in the interstellar medium, providing robust explanations for observed abundances in cold cores, such as TMC-1 (CP). In particular, it highlights the role of non-diffusive chemistry in the production of gas-phase COMs on grain surfaces, which are subsequently chemically desorbed, especially when the precursors involved in their formation on the surfaces are heavier than atomic hydrogen.