Metals and ionizing photons from dwarf galaxies

We estimate the potential contribution of M <10(9)M(circle dot) dwarf galaxies to the reionization and early metal enrichment of the Milky Way environment, or circum-Galactic medium. Our approach is to use the observed properties of ancient stars ()under tilde>12 Gyr old) measured in nearby dwarf galaxies to characterize the star formation at high z. We use a merger-tree model for the build-up of the Milky Way, which self-consistently accounts for feedback processes, and which is calibrated to match the present-day properties of the Galaxy and its dwarf satellites. We show that the high-z analogues of nearby dwarf galaxies can produce the bulk of ionizing radiation (> 80 per cent) required to reionize theMilkyWay environment. Our fiducial model shows that the gaseous environment can be 50 per cent reionized at z approximate to 8 by galaxies with 10(7) M-circle dot