Two epochs of globular cluster formation from deep field luminosity functions: implications for reionization and the Milky Way satellites

Our results suggest that: (i) the bulk of the old globular cluster population with estimated ages greater than or similar to 12 Gyr (about 50 per cent of the total population) formed in the relatively massive dwarf galaxies at redshifts z greater than or similar to 6; (ii) proto-GC formation was an important mode of star formation in those dwarf galaxies, and likely dominated the reionization process. Another consequence of this scenario is that some of the most massive Milky Way satellites may be faint and yet undiscovered because tidal stripping of a dominant GC population precedes significant stripping of the dark matter haloes of these satellites. This scenario may alleviate some remaining tensions between cold dark matter simulations and observations.