The Full-fledged Dwarf Irregular Galaxy Leo A

We have studied Leo A, an isolated and extremely gas-rich dwarf irregular galaxy of very low stellar mass and metallicity. Ages of the stellar populations in Leo A range from ~10 Myr to ~10 Gyr. Here we report the discovery of an old stellar halo and a sharp stellar edge. We also find that the distribution of stars extends beyond the gaseous envelope of the galaxy. Therefore, by its structure as well as stellar and gaseous content, Leo A is found to resemble massive disk galaxies. This implies that galaxies of very low stellar mass are also able to develop complex structures, challenging contemporary understanding of galaxy evolution.