Validating Semi-Analytic Models of High-Redshift Galaxy Formation using
  Radiation Hydrodynamical Simulations
  We use a cosmological hydrodynamic simulation calculated with Enzo and the
semi-analytic galaxy formation model (SAM) GAMMA to address the chemical
evolution of dwarf galaxies in the early universe. The long-term goal of the
project is to better understand the origin of metal-poor stars and the
formation of dwarf galaxies and the Milky Way halo by cross-validating these
theoretical approaches. We combine GAMMA with the merger tree of the most
massive galaxy found in the hydrodynamic simulation and compare the star
formation rate, the metallicity distribution function (MDF), and the
age-metallicity relationship predicted by the two approaches. We found that the
SAM can reproduce the global trends of the hydrodynamic simulation. However,
there are degeneracies between the model parameters and more constraints (e.g.,
star formation efficiency, gas flows) need to be extracted from the simulation
to isolate the correct semi-analytic solution. Stochastic processes such as
bursty star formation histories and star formation triggered by supernova
explosions cannot be reproduced by the current version of GAMMA. Non-uniform
mixing in the galaxy's interstellar medium, coming primarily from
self-enrichment by local supernovae, causes a broadening in the MDF that can be
emulated in the SAM by convolving its predicted MDF with a Gaussian function
having a standard deviation of ~0.2 dex. We found that the most massive galaxy
in the simulation retains nearby 100% of its baryonic mass within its virial
radius, which is in agreement with what is needed in GAMMA to reproduce the
global trends of the simulation.
