Uncertainties in supernova input rates drive qualitative differences in
  simulations of galaxy evolution
  Feedback from core collapse supernovae (SNe), the final stage of evolution of
massive stars, is a key element in galaxy formation theory. The energy budget
of SN feedback, as well as the duration over which SNe occur, are constrained
by stellar lifetime models and the minimum mass star that ends its life as a
SN. Simplifying approximations for this SN rate are ubiquitous in simulation
studies. We show here how the choice of SN budget and timings ($t_0$ for the
delay between star formation and the first SN, $\tau_{\rm SN}$ for the duration
of SN injection, and the minimum SN progenitor mass) drive changes in the
regulation of star formation and outflow launching. Extremely long delays for
instantaneous injection of SN energy $(t_0 << 20\;\rm{Myr})$ reduces star
formation and drive stronger outflows compared smaller delays. This effect is
primarily driven by enhanced clustering of young stars. With continuous
injection of energy, longer SN durations results in a larger fraction of SN
energy deposited in low ambient gas densities, where cooling losses are lower.
This is effect is particularly when driven by the choice of the minimum SN
progenitor mass, which also sets the total SN energy budget. These underlying
uncertainties mean that despite advances in the sub-grid modeling of SN
feedback, serious difficulties in constraining the strength of SN feedback
remain. We recommend future simulations use realistic SN injection durations,
and bound their results using SN energy budgets and durations for minimum SN
progenitors of $7M_\odot$ and $9M_\odot$.
