title: The universe at z > 5: when and how did the "dark age" end?
abstract: This paper considers how the first subgalactic structures produced the UV radiation that ionized the intergalactic medium before z = 5 and the "feedback" effects of the UV radiation on structure formation. The first "pregalaxies" may eventually be detectable by their direct UV emission, with characteristic spectral features at Lyman alpha; high-z supernovae may also be detectable. Other probes of the intergalactic medium beyond z = 5, and of the epochs of reheating and reionization, are discussed, along with possible links between the diffusion of pregalactic metals and the origin of magnetic fields.
authors.affiliation: Institute of Astronomy, Madingley Road, Cambridge, CB3 OHA, United Kingdom.
authors.forename: M J
authors.initials: MJ
authors.lastname: Rees