A semiempirical approach to low-energy cosmic ray propagation in the diffuse interstellar medium

Abstract

We investigate the ionization of the diffuse interstellar medium by cosmic rays by modeling their propagation along the wandering magnetic fields using a Monte Carlo method. We study how low-energy cosmic rays propagate in turbulent, translucent molecular clouds, and how they regulate the ionization and both lose and gain energy from the medium. As a test case, we use high spatial resolution (0.03 pc) CO maps of a well-studied high latitude translucent cloud, MBM 3, to model turbulence. The propagation problem is solved with a modified Monte Carlo procedure that includes trapping, energization, and ionization losses. In a homogeneous medium, trapping and re-energization do not produce a significant effect. In a nonuniform medium, particles can be trapped for a long time inside the cloud. This modifies the cosmic ray distribution due to stochastic acceleration at the highest energies (about 100 MeV). At lower energies, the re-energization is too weak to produce an appreciable effect. The change in the energy distribution does not significantly affect the ionization losses, so ionization changes are due to trapping effects.

arXiv comment8 pages, 13 figures

References in corpus (11)

• Cosmic-ray ionization of molecular clouds
• Wave damping by MHD turbulence and its effect upon cosmic ray propagation in the ISM
• Turbulence-induced magnetic fields and the structure of Cosmic Ray modified shocks
• Velocity Field Statistics in Star-Forming Regions. I. Centroid Velocity Observations
• The Interaction of Cosmic Rays with Diffuse Clouds
• Confinement-Driven Spatial Variations in the Cosmic Ray Flux
• Penetration of cosmic rays into dense molecular clouds: role of diffuse envelope
• The role of cosmic rays on magnetic field diffusion and the formation of protostellar discs
• Power requirements for cosmic ray propagation models involving re-acceleration and a comment on second order Fermi acceleration theory
• Superdiffusive Stochastic Fermi Acceleration in Space and Energy
• Cosmic ray penetration in diffuse clouds