Stellar orbits and the survival of metallicity gradients in simulated
  dwarf galaxies
  We present a detailed analysis of the formation, evolution, and possible
longevity of metallicity gradients in simulated dwarf galaxies. Specifically,
we investigate the role of potentially orbit-changing processes such as radial
stellar migration and dynamical heating in shaping or destroying these
gradients. We also consider the influence of the star formation density
threshold, investigating both a low and high value (0.1 amu/$cm^{3}$ - 100
amu/$cm^{3}$).
  The Nbody-SPH models that we use to self-consistently form and evolve dwarf
galaxies in isolation show that, in the absence of significant angular
momentum, metallicity gradients are gradually built up during the evolution of
the dwarf galaxy, by ever more centrally concentrated star formation adding to
the overall gradient. Once formed, they are robust, survive easily in the
absence of external disturbances and hardly decline over several Gyr, and they
agree well with observed metallicity gradients of dwarf galaxies in the Local
Group. The underlying orbital displacement of stars is quite limited in our
models, being of the order of only fractions of the half light radius over
time-spans of 5 to 10 Gyr in all star formation schemes. This is contrary to
the strong radial migration found in massive disc galaxies, caused by
scattering of stars off the corotation resonance of spiral structures. In the
dwarf regime the stellar body only seems to undergo mild dynamical heating, due
to the lack of long-lived spiral structures and/or discs.
  The density threshold has profound influences on the star formation mode of
the models, but only a minor influence on the evolution of metallicity
gradients. Increasing the threshold 1000-fold causes comparatively stronger
dynamical heating of the stellar body due to the increased turbulence and the
scattering of stars off dense gas clouds, but the effect remains very limited
in absolute terms.
