Speaker
Description
The microphysics of cosmic ray (CR) propagation in complex, magnetized interstellar media remains unsettled. CR pressure gradients can self-generate magneto-sonic turbulence, promoting diffusion, while ion-neutral damping in dense regions suppresses this turbulence, favoring ballistic transport. The interplay between these processes across the hierarchical structure of the interstellar medium (ISM) governs how strongly CRs interact with different components of molecular cloud complexes, and determines their role in regulating the physical, thermal, and chemical evolution of ISM clouds. Recent gamma-ray observations and ionization rate measurements of nearby Galactic molecular clouds suggest that CR transport in dense clumps deviates from both purely ballistic and purely diffusive behavior. To investigate this, we present a self-consistent model of CR transport and interactions in magnetized molecular clouds, testing three CR propagation regimes: ballistic, diffusive, and a hybrid configuration featuring a diffusive envelope with a ballistic core. By computing ionization rates and gamma-ray signatures of CRs traversing parameterized cloud environments, we show that Fermi-LAT data and ionization measurements of nearby molecular cloud complexes are best explained by a combination of diffusive transport in turbulent envelopes and a transition to ballistic propagation in dense cores. Moreover, we find that the structure of the diffusive envelope must vary between individual clouds to consistently account for both the gamma-ray and ionization constraints. Our results establish an efficient new framework for interpreting multi-wavelength observations of CR interactions in molecular clouds and offer a path toward systematically constraining the physics of CR transport in dense ISM environments and its environmental dependence.
