Towards the Next Generation in Cosmic Ray Astrochemistry

• Applicant: Brandt Gaches, Ph.D.
• Subject Area: Astrophysics and Astronomy
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 542802847

Energetic particles, called cosmic rays (CRs), in particular low-energy ions with energies below 1 GeV/nucleon, are significant drivers of the thermochemistry of the dense molecular gas stars form from. Low-energy CRs produce a diverse zoo of molecules through a combination of ion-neutral chemistry, induced radiation and electron production, and interactions with icy grains. Interactions between CRs and icy grains are thought to enhance the production of complex organic molecules in cold gas. Through ionization processes, CRs regulate the strength of important non-ideal processes, such as ambi-polar and Ohmic diffusion, thought to be crucial for the formation of disks around accreting young stars. Therefore, constraining the flux of low-energy CRs and their interactions with dense gas and icy grains is crucial towards advancing our understanding of the formation of stars and planets. Despite their importance, low-energy CRs are often included very simply into astrochemical models of the molecular universe. Most often, it is assumed that the flux of low-energy CRs is a global constant with some presumed spectral shape. The next generation of astrochemical models necessitate a significant advancement in the treatment of CRs. I propose here to investigate the roles of CRs on molecular chemistry through developing more advanced astrochemistry software incorporating spectrum-resolved treatments of CR transport and physical processes. These tools will necessitate the aggregation and creation of more fundamental data of CR interactions, in particular ionization and excitation cross sections for gas phase and CR energy depositions in grains. These will be used to produce astrochemical models utilizing both steady-state prescriptions for parameter space investigations and post-processing multi-physics star formation simulations. The astrochemical models will investigate the role of CRs in three key aspects of chemistry: the carbon cycle (C+/C/CO) of molecular clouds, the trail of water from cloud to core scales, and the emergence of complex organic chemistry. The results of these novel investigations will provide key insights the interactions of low-energy cosmic rays in dense molecular gas and the role they play in key chemical processes. This proposal will train three PhD students with interdisciplinary theses and prepare one postdoctoral researcher for a higher academic positions and produce public software and data to improve future astrochemical models incorporating cosmic rays.

• DFG Programme: Independent Junior Research Groups
• International Connection: USA
• Participating Person: Professor Christopher Shingledecker, Ph.D.