These simulations include self-consistent cosmic ray injection, transport, and feedback in gas. This is the 'single bin' model that represents cosmic rays with a single energy density, roughly the energy of cosmic-ray protons near the peak of the spectrum at 1-10 GeV. These simulations use the cosmic-ray diffusion coefficient that best fits gamma-ray observations, kappa = 3e29 cm^2 g^-1 (or 700 in Gizmo's code units). This value of kappa also produces the most meaningful differences from the simulations with only MHD+.

These simulations also include MHD+, magnetohydrodynamics as well as fully-anisotropic Spitzer-Braginskii conduction and viscosity.

We ran these simulations after we fixed the cosmic-ray heating bug in Gizmo (after 2018-4-26). That bug erroneously applied a heating term from cosmic rays to all gas in the simulation at z >~ 8, which prevented gas cooling and star formation at those early times, and which affects other FIRE-2 simulations.

Most of these MHD+ and Cosmic Ray simulations have a subset of 61 out of 601 snapshots available, specifically, every tenth snapshot. However, this simulation has all 601 snapshots available.