Metallicity Distribution Functions of Four Local Group dwarf galaxies
  We present stellar metallicities in Leo I, Leo II, IC 1613, and Phoenix dwarf
galaxies derived from medium (F390M) and broad (F555W, F814W) band photometry
using the Wide Field Camera 3 (WFC3) instrument aboard the Hubble Space
Telescope. We measured metallicity distribution functions (MDFs) in two ways,
1) matching stars to isochrones in color-color diagrams, and 2) solving for the
best linear combination of synthetic populations to match the observed
color-color diagram. The synthetic technique reduces the effect of photometric
scatter, and produces MDFs 30-50 % narrower than the MDFs produced from
individually matched stars. We fit the synthetic and individual MDFs to
analytical chemical evolution models (CEM) to quantify the enrichment and the
effect of gas flows within the galaxies. Additionally, we measure stellar
metallicity gradients in Leo I and II. For IC 1613 and Phoenix our data do not
have the radial extent to confirm a metallicity gradient for either galaxy.
  We find the MDF of Leo I (dwarf spheroidal) to be very peaked with a steep
metal rich cutoff and an extended metal poor tail, while Leo II (dwarf
spheroidal), Phoenix (dwarf transition) and IC 1613 (dwarf irregular) have
wider, less peaked MDFs than Leo I. A simple CEM is not the best fit for any of
our galaxies, therefore we also fit the `Best Accretion Model' of Lynden-Bell
1975. For Leo II, IC 1613 and Phoenix we find similar accretion parameters for
the CEM, even though they all have different effective yields, masses, star
formation histories and morphologies. We suggest that the dynamical history of
a galaxy is reflected in the MDF, where broad MDFs are seen in galaxies that
have chemically evolved in relative isolation and narrowly peaked MDFs are seen
in galaxies that have experienced more complicated dynamical interactions
concurrent with their chemical evolution.
