Semi-analytic galaxies -- III. The impact of supernova feedback on the
  mass-metallicity relation
  We use the semi-analytic model (SAM) of galaxy formation and evolution SAG
coupled with the MULTIDARK simulation MDPL2 to study the evolution of the
stellar mass-gas metallicity relation of galaxies (MZR). We test several
implementations of the dependence of the mass loading due to supernovae (SNe).
We find that no evolution in the normalization of the MZR is obtained unless we
introduce an explicit scaling of the reheated and ejected mass with redshift as
$(1+z)^\beta$. The latter is in agreement with results from the FIRE
simulations, and it should encompass small scale properties of the interstellar
medium varying over time, which are not captured in SAMs, as well as other
energy sources in addition to SNe. Increasing $\beta$ leads to stronger
evolution of the MZR normalization; $\beta = 1.9$ reproduces the observed MZR
in the range $0 < z < 3.5$. A stronger redshift dependence of outflows reduces
the levels of star formation at earlier epochs with the consequent decrease of
metal production. This leads to a slower increase of the gas metallicity
compared to the stellar mass build-up. The cold gas can be contaminated either
by receiving a direct injection of the material recycled by stellar winds and
SNe or by gas cooling. The relative role of each process for a given stellar
mass depends on the criterion adopted to regulate the fate of the recycled
material. However, modifying the metal loading of the outflows has mild impact
on the zero-point evolution and does not affect our conclusions.
