The history of stellar metallicity in a simulated disc galaxy
  We explore the chemical distribution of stars in a simulated galaxy. Using
simulations of the same initial conditions but with two different feedback
schemes (MUGS and MaGICC), we examine the features of the age-metallicity
relation (AMR), and the three-dimensional age-metallicity-[O/Fe] distribution,
both for the galaxy as a whole and decomposed into disc, bulge, halo, and
satellites. The MUGS simulation, which uses traditional supernova feedback, is
replete with chemical substructure. This sub- structure is absent from the
MaGICC simulation, which includes early feedback from stellar winds, a modified
IMF and more efficient feedback. The reduced amount of substructure is due to
the almost complete lack of satellites in MaGICC. We identify a significant
separation between the bulge and disc AMRs, where the bulge is considerably
more metal-rich with a smaller spread in metallicity at any given time than the
disc. Our results suggest, however, that identifying the substructure in
observations will require exquisite age resolution, on the order of 0.25 Gyr.
Certain satellites show exotic features in the AMR, even forming a 'sawtooth'
shape of increasing metallicity followed by sharp declines which correspond to
pericentric passages. This fact, along with the large spread in stellar age at
a given metallicity, compromises the use of metallicity as an age indicator,
although alpha abundance provides a more robust clock at early times. This may
also impact algorithms that are used to reconstruct star formation histories
from resolved stellar populations, which frequently assume a
monotonically-increasing AMR.
