Intrusion of MeV–TeV Cosmic Rays into Molecular Clouds Studied by Ionization, the Neutral Iron Line, and Gamma Rays

Low-energy (~MeV) cosmic rays (CRs) ionize molecular clouds and create the neutral iron line (Fe I K\alpha) at 6.4 keV. On other hand, high-energy (>~ GeV) CRs interact with dense cloud gas produce gamma rays. Based on a one-dimensional model, we study spatial correlation among ionization rates of gas, keV fluxes, gamma-ray emissions from illuminated by accelerated an adjacent supernova remnant. We find that distributions these three observables depend how intrude internal structure cloud. If intrusion is represented slow diffusion, should be detected around edge where are high. if freely stream in cloud, observed emitted. In former, cooling time responsible for shorter than their crossing time, it opposite latter. Although compare results observations, cannot conclude whether diffusion or free-streaming dominantly realized. Our predictions can checked more detail future X-ray missions such as XRISM Athena observations cover wider fields.