Spectrally resolved cosmic rays

Cosmic rays (CRs) are an important component in the interstellar medium (ISM), which can heat and ionize the gas in dense star forming cores, alter the diffuse ISM and drive glactic outflows. The energy of CRs range from just above the thermal distribution in the non-relativistic regime up to the ultra-relativistic part with momenta up to 10²⁰ eV. The details of the impact of CRs, they interaction with the gas, the cooling rates and transport properties strongly depend on the momentum of the CRs. Low energy CRs ionize the gas and can cool efficiently via Coulomb and ionization losses. GeV CRs contain most of the CR energy, which is comparable to the other energy components in the ISM and can have a direct dynamical impact. Ultra-relativistic CRs do not dominate in total energy, but provide important observational links via e.g. gamma rays.

In numerical simulations we would like to accurately incorporate CRs from the non-relativistic up to the ultra-relativistic limit. Ideally we would like to include a full spectrum in every computational, which requires to cover the large range in CR energies and the large dynamic range in the spectrum with efficient numerical methods. I have been working an efficient model that allows to compute the main proton processes including Coulomb & ionization losses, adiabatic processes and hadronic losses. The numerical model and an application to galaxies is published here:

• Girichidis et al. 2020, MNRAS 491, 993
• Girichidis et al. submitted to MNRAS