A signature of the internal reionisation of the Milky Way?
  We present a new semi-analytical model of the population of satellite
galaxies of the Milky Way, aimed at estimating the effect of the spatial
structure of reionisation at galaxy scale on the properties of the satellites.
In this model reionisation can be either: (A) externally-driven and uniform, or
(B) internally-driven, by the most massive progenitor of the Milky-Way. In the
latter scenario the propagation of the ionisation front and photon dilution
introduce a delay in the photo-evaporation of the outer satellites' gas with
respect to the inner satellites. As a consequence, outer satellites experience
a longer period of star formation than those in the inner halo. We use simple
models to account for star formation, the propagation of the ionisation front,
photo-evaporation and observational biases. Both scenarios yield a model
satellite population at z=0 that matches the observed luminosity function and
mass-to-light ratios. However, the predicted population for scenario (B) is
significantly more extended spatially than for scenario (A), by about 0.3 dex
in distance, resulting in a much better match to the observations. The survival
of this structural signature imprinted by the local UV field during
reionisation on the radial distribution of satellites makes it a promising tool
for studying the reionisation epoch at galaxy scale in the Milky Way and nearby
galaxies resolved in stars with forthcoming large surveys. However, more work
is needed to determine how the effect reported here can be disentangled from
that of cosmic variance between different realisations of Milky Way haloes.
