These simulations use a modified version of the original UV background (Faucher-Giguere et al. 2009) that we used in all other FIRE-2 simulations. We modified this UV background only at z > 6 (it is the same at z < 6), such that hydrogen reionization occurs at z = 7.8, instead of z ~ 10 in the original UV background.

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.

For these versions of m12i, m12f, and m12m, all particles additionally store their 3-D acceleration.