DDO 187: Do dwarf galaxies have extended halos?

Abstract

If dwarf galaxies are primeval objects in the Universe, as hierarchical galaxy formation scenarios predict, they should show traces of their old stellar populations, perhaps distributed in extended, differentiated structures. The working hypothesis that such a structure could exist is tested for the case of DDO 187, a field dIrr galaxy showing a high gas fraction and low metallicity. For this purpose, the structure, star formation history (SFH) and other properties of the galaxy are analyzed using the spatial distribution of stars, the color-magnitude diagrams (CMDs) of about 1500 resolved stars and the fluxes of Hii regions, together with data about the gas distribution. The distance of DDO 187 has been also computed and has been found to 2.5 Mpc; three times smaller than a previous estimate based on Cepheid stars.