Constraining Sub-Grid Physics with High-Redshift Spatially-Resolved
  Metallicity Distributions
  We examine the role of energy feedback in shaping the distribution of metals
within cosmological hydrodynamical simulations of L* disc galaxies. While
negative abundance gradients today provide a boundary condition for galaxy
evolution models, in support of inside-out disc growth, empirical evidence as
to whether abundance gradients steepen or flatten with time remains highly
contradictory. We made use of a suite of L* discs, realised with and without
`enhanced' feedback. All the simulations were produced using the smoothed
particle hydrodynamics code Gasoline, and their in situ gas-phase metallicity
gradients traced from redshift z~2 to the present-day. Present-day
age-metallicity relations and metallicity distribution functions were derived
for each system. The `enhanced' feedback models, which have been shown to be in
agreement with a broad range of empirical scaling relations, distribute energy
and re-cycled ISM material over large scales and predict the existence of
relatively `flat' and temporally invariant abundance gradients. Enhanced
feedback schemes reduce significantly the scatter in the local stellar
age-metallicity relation and, especially, the [O/Fe]-[Fe/H] relation. The local
[O/Fe] distribution functions for our L* discs show clear bimodality, with
peaks at [O/Fe]=-0.05 and +0.05 (for stars with [Fe/H]>-1), consistent with our
earlier work on dwarf discs. Our results with `enhanced' feedback are
inconsistent with our earlier generation of simulations realised with
`conservative' feedback. We conclude that spatially-resolved metallicity
distributions, particularly at high-redshift, offer a unique and under-utilised
constraint on the uncertain nature of stellar feedback processes.
