Cosmic ray propagation in diffuse clouds.
This study aims to answer the question on how effectively low energy CRs (in this context energy < 1 GeV) can penetrate into diffuse clouds when they come from the fully ionized interstellar medium (ISM). The amount of CRs entering the cloud determines the ionization rate inside the cloud itself, affecting its chemistry. When CRs start penetrating the cloud, the ionization losses (mainly due to ionization of H2 molecule) produce a negative gradient in the spatial distribution of CRs. The presence of a gradient drives the excitation of Alfvén waves through the streaming instability, the same waves which are responsible for the scattering of CRs. As a consequence, immediately outside the cloud, CRs produce a thin layer of enhanced magnetic turbulence (i.e. Alfvén waves) where CRs are scattered more effectively, remaining trapped for a while. Due to this trapping, the amount of energy losses due to ionization increases, and particles below a fixed energy threshold will never enter into the cloud. The energy threshold mainly depends on the external CRs flux and on the density profile of the cloud. This phenomenon could have important implication for the penetration of CRs into clouds close to SNR, where the density of CRs is higher.
Study of ionization induced by CRs in molecular clouds as a function of the CR spectrum.
In the current literature, the ionization rate of chemicals inside a MC is calculated assumed a fixed spectrum of CRs. The accepted bias is that the Galactic CR spectrum is the same everywhere in the Galaxy. This assumption is expected to fail in the vicinity of a SNR, where the flux of CRs should be dominated by those escaping from the SNR, rather than by the average Galactic contribution. Hence, a correct calculation of the ionization rate in these MCs located close to SNRs, requires the use of the right CR spectrum. Our idea is to build a software able to calculate the ionization rate of H2, and possibly other chemicals, using an arbitrary CR spectrum as input. With respect to the current literature we will also implement improved versions of the ionization cross section of H2 molecule due to collision with electrons and protons.