Searching for the reionization sources

ABSTRACT Using a reionization model simultaneously accounting for a number of experimental datasets, we investigate the nature and properties of reionization sources. Such model predictsthat hydrogen reionization starts at z ≈ 15, is initially driven by metal-free (PopIII) stars, andis 90% complete by z ≈ 8. We find that a fraction f γ > 80% of the ionizing power at z ≥ 7comes from haloes of mass M 10 9 M ⊙ haloes, yielding f γ ≈ 60% at z = 6. Using Lyman-break broadband dropout techniques,J-banddetection of sources contributingto 50% (90%) of the ionizing powerat z ∼ 7.5requiresto reach a magnitude J 110,AB = 31.2(31.7), where ∼ 15(30) (PopIII) sources/arcmin 2 arepredicted. We conclude that z > 7 sources tentatively identified in broadband surveys arerelatively massive (M ≈ 10 9 M ⊙ ) and rare objects which are only marginally (≈ 1%) addingto the reionization photon budget.Key words: intergalactic medium cosmology: theory large-scale structure of Universe.