On the nature of the Milky Way satellites
  We combine a series of high-resolution simulations with semi-analytic galaxy
formation models to follow the evolution of a system resembling the Milky Way
and its satellites. The semi-analytic model is based on that developed for the
Millennium Simulation, and successfully reproduces the properties of galaxies
on large scales, as well as those of the Milky Way. In this model, we are able
to reproduce the luminosity function of the satellites around the Milky Way by
preventing cooling in haloes with Vvir < 16.7 km/s (i.e. the atomic hydrogen
cooling limit) and including the impact of the reionization of the Universe.
The physical properties of our model satellites (e.g. mean metallicities, ages,
half-light radii and mass-to-light ratios) are in good agreement with the
latest observational measurements. We do not find a strong dependence upon the
particular implementation of supernova feedback, but a scheme which is more
efficient in galaxies embedded in smaller haloes, i.e. shallower potential
wells, gives better agreement with the properties of the ultra-faint
satellites. Our model predicts that the brightest satellites are associated
with the most massive subhaloes, are accreted later (z $\lta$ 1), and have
extended star formation histories, with only 1 per cent of their stars made by
the end of the reionization. On the other hand, the faintest satellites were
accreted early, are dominated by stars with age > 10 Gyr, and a few of them
formed most of their stars before the reionization was complete. Objects with
luminosities comparable to those of the classical MW satellites are associated
with dark matter subhaloes with a peak circular velocity $\gta$ 10 km/s, in
agreement with the latest constraints.
