Invited Talk - Splinter CosmicRays

Monday, 13 September 2021, 10:15   (virtual Cosmic)

Constraining the physics of cosmic ray transport in dense gas

Kedron Silsbee
Max Planck Institute for Extraterrestrial Physics

Cosmic rays are very influential to the chemistry and dynamics of the molecular gas which forms young stellar systems. Despite this, their abundance, particularly in denser regions, remains uncertain. Although cosmic rays are not directly observable, we can infer their presence in molecular clouds from chemical tracers of gas ionization, gamma ray and synchrotron emission, enhanced gas temperature, and excited ro-vibrational states of H2. These suggest that while cosmic rays above approximately 1 GeV propagate freely into clouds, lower energy cosmic rays are excluded from the denser gas. This is qualitatively in agreement with predictions from theoretical models of cosmic ray attenuation. However, depending on the physics that dominates the propagation, the degree of attenuation varies significantly, and current data is insufficient to distinguish between the models. In this talk I will give an overview of the different transport regimes thought to play a role (diffusion, free propagation, and streaming), and what predictions these make for the variation of the ionization rate. I will then discuss the ways future observations may be able to constrain the dominant propagation regime.