We present the first detailed structure formation and radiative transfer
simulations of the reionization history of our cosmic neighbourhood. To this
end, we follow the formation of the Local Group of galaxies and nearby clusters
by means of constrained simulations, which use the available observational
constraints to construct a representation of those structures which reproduces
their actual positions and properties at the present time. We find that the
reionization history of the Local Group is strongly dependent on the assumed
photon production efficiencies of the ionizing sources, which are still poorly
constrained. If sources are relatively efficient, i.e. the process is
'photon-rich', the Local Group is primarily ionized externally by the nearby
clusters. Alternatively, if the sources are inefficient, i.e. reionization is
'photon-poor' the Local Group evolves largely isolated and reionizes itself.
The mode of reionization, external vs. internal, has important implications for
the evolution of our neighbourhood, in terms of e.g. its satellite galaxy
populations and primordial stellar populations. This therefore provides an
important avenue for understanding the young universe by detailed studies of
our nearby structures.Comment: 10 pages, 8 figures (all in colour), submitted to MNRA
