Star formation and gas flow history of a dwarf irregular galaxy traced
  by gas-phase and stellar metallicities
  Studying the evolution of dwarf galaxies can provide insights into the
characteristics of systems that can act as building blocks of massive galaxies.
This paper discusses the history of star formation and gas flows (inflow and
outflow) of a dwarf irregular galaxy in the Local Group, NGC 6822, from the
viewpoint of gas-phase and stellar chemical abundance. Gas-phase oxygen
abundance, stellar metallicity distribution and gas fraction data are compared
to chemical evolution models in which continuous star formation and gas flows
are assumed. If the galaxy is assumed to be a closed or an accretion-dominated
system where steeper stellar initial mass functions are allowed, the observed
gas-phase oxygen abundance and gas fraction can be explained simultaneously;
however metallicity distributions predicted by the models seem to be
inconsistent with the observed distribution, which suggests that the star
formation, gas flows and/or chemical enrichment are more complex than assumed
by the models. When NGC 6822 is assumed to be a system dominated by outflow,
the observed values of gas-phase oxygen abundance and gas fraction can be
explained, and the metallicity distributions predicted by some of the models
are also roughly consistent with the observed distribution in the metallicity
range of -2.0<[Fe/H]<-0.5. It should be noted that this result does not
necessarily mean that the accretion of gas is completely ruled out. More
observables, such as chemical abundance ratios, and detailed modelling may
provide deeper insight into the evolution of the system.
