Metals and ionizing photons from dwarf galaxies
  We estimate the potential contribution of M < 10^9 Msun 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 (> 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%) required to reionize the
Milky Way environment. Our fiducial model shows that the gaseous environment
can be 50% reionized at z ~ 8 by galaxies with 10^7 Msun < M < 10^8 Msun. At
later times, radiative feedback stops the star-formation in these small
systems, and reionization is completed by more massive dwarf galaxies by z_rei
= 6.4\pm 0.5. The metals ejected by supernova-driven outflows from M < 10^9
Msun dwarf galaxies almost uniformly fill the Milky Way environment by z ~ 5,
enriching it to Z ~ 2 10^-2 Zsun. At z ~ 2 these early metals are still found
to represent ~ 50% of the total mass of heavy elements in the circum-Galactic
Medium.
