The Universe at $Z > 5$: when and how did the `Dark Age' End?
  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 relevance of pregalactic activity to heavy element production and the origin of magnetic fields is briefly addressed. 
Martin J. Rees