How Metals Are Transported In And Out Of A Galactic Disk: Dependence On
  The Hydrodynamic Schemes In Numerical Simulations
  Metallicity is a fundamental probe for understanding the baryon physics in a
galaxy. Since metals are intricately associated with radiative cooling, star
formation, and feedback, reproducing the observed metal distribution through
numerical experiments will provide a prominent way to examine our
understandings of galactic baryon physics. In this study, we analyze the
dependence of the galactic metal distribution on the numerical schemes and
quantify the differences in the metal mixing among modern galaxy simulation
codes (the mesh-based code Enzo and the particle-based codes Gadget-2 and
Gizmo-PSPH). In particular, we examine different stellar feedback strengths and
an explicit metal diffusion scheme in particle-based codes, as a way to
alleviate the well-known discrepancy in metal transport between mesh-based and
particle-based simulations. We demonstrate that a sufficient number of gas
particles are needed in the gas halo to properly investigate the metal
distribution therein. Including an explicit metal diffusion scheme does not
significantly affect the metal distribution in the galactic disk but does
change the amount of low-metallicity gas in the hot-diffuse halo. We also find
that the spatial distribution of metals depends strongly on how the stellar
feedback is modeled. We demonstrate that the previously reported discrepancy in
metals between mesh-based and particle-based simulations can be mitigated with
our proposed prescription, enabling these simulations to be reliably utilized
in the study of metals in galactic halos and the circumgalactic medium.
