Modeling supernova feedback in galaxy formation simulations with energy-conserving momentum injection

Abstract Accurate modeling of supernova (SN) feedback in galaxy formation simulations is complicated by energy conservation violations arising from the vector nature of momentum injection. We present a mechanical feedback scheme addressing two key sources: the relative motion between gas elements and the SN-hosting star particle, and multiple momentum injections into a single gas element within one timestep. Computing the kinetic energy increment in the rest frame of the gas element ensures energy conservation while avoiding the momentum inversion that can occur when this calculation is instead performed in the lab frame. This correction inherently violates momentum conservation, disturbing the angular momentum distribution and hindering disk formation when momentum is coupled on galactic scales. To prevent unphysical large-scale momentum coupling without an ad hoc maximum coupling radius, we switch to purely thermal feedback when the cooling radius is resolved by the local inter-element separation. Our scheme is designed for high- to intermediate-resolution zoom-in simulations with star particle masses up to ${\sim }10^5\, {M}_\odot$. Through cosmological zoom-in simulations of dwarf galaxies ($M_\mathrm{vir} \sim 10^{11}\, {M}_\odot$) at two mass resolutions, we demonstrate good convergence in star formation histories; without the momentum correction, stellar mass in low-resolution runs falls to as low as 59% of that in high-resolution counterparts. At the feedback strength reproducing dwarf galaxy stellar masses, a Milky Way-mass simulation overproduces stellar mass, suggesting additional processes, such as active galactic nuclei feedback, are required at this mass scale.