  Using a reionization model simultaneously accounting for a number of
experimental data sets, we investigate the nature and properties of
reionization sources. Such model predicts that hydrogen reionization starts at
z \approx 15, is initially driven by metal-free (PopIII) stars, and is 90%
complete by z \approx 8. We find that a fraction f_\gamma >80% of the ionizing
power at z > 7 comes from haloes of mass M<10^9 M_sun predominantly harbouring
PopIII stars; a turnover to a PopII-dominated phase occurs shortly after, with
this population, residing in M>10^9 M_sun haloes, yielding f_\gamma \approx 60%
at z=6. Using Lyman-break broadband dropout techniques, J-band detection of
sources contributing to 50% (90%) of the ionizing power at z \sim 7.5 requires
to reach a magnitude J_{110,AB} = 31.2 (31.7), where about 15 (30) (PopIII)
sources/arcmin^2 are predicted. We conclude that z>7 sources tentatively
identified in broadband surveys are relatively massive (M \approx 10^9 M_sun)
and rare objects which are only marginally (\approx 1%) adding to the
reionization photon budget.
