Searching for the reionization sources

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