Propagation of Low-Energy Cosmic Rays in Molecular Clouds: Calculations in Two Dimensions

TL;DR

This paper models the transport of low-energy cosmic rays in molecular clouds using a 2D Boltzmann equation approach coupled with MHD simulations, revealing steady-state distributions and ionization effects.

Contribution

It introduces a novel 2D computational framework combining Boltzmann transport with MHD to study cosmic ray propagation in molecular clouds.

Findings

Steady-state cosmic ray distributions achieved in simulations

Ionization rates of interstellar hydrogen calculated

Impact of anisotropic cosmic ray flux on cloud ionization

Abstract

We calculate cosmic ray transport with a collisional Boltzmann Transport Equation, including E-M forces. We apply the Crank-Nicholson Method to solve this equation. At each time step, the spatial distribution of cosmic rays is applied to the ZEUS 2D magnetohydrodynamics model, which is then utilized to calculate the resulting E-M field. Finally, the field is applied to the initial equation. This sequence is repeated over many time steps until a steady state is reached. We consider results from t = 0 until steady state for an isotropic low energy cosmic ray flux, and also for an enhanced cosmic ray flux impinging on one side of a molecular cloud. This cosmic ray flux is used to determine an ionization rate of interstellar hydrogen by cosmic rays, zeta. Astrochemical implications are briefly mentioned.