For ``Physics Reports'' special issue in memory of D.N. Schramm; (astro-ph/9912345)
Abstract. The universe would have been completely dark between
the epoch of
recombination and the development of the first non-linear
structure. But at redshifts beyond 5 - perhaps even beyond 20 -
stars formed within `subgalaxies' and created the first heavy
elements; these same systems (together perhaps with `miniquasars')
generated the UV radiation that ionized the IGM, and maybe also the
first significant magnetic fields. Although we can already probe back
to z 
5, these very
first objects may be so faint that their
detection must await next-generation optical and infrared
telescopes. Observations in other wavebands may offer indirect clues
to when reionization occurred. Despite the rapid improvements in
numerical simulations, the processes of star formation and feedback
are likely to remain a challenge for the next decade.
Table of Contents
INTRODUCTION
COSMOGONIC PRELIMINARIES: MOLECULAR HYDROGEN AND UV
FEEDBACK
The H2 Cooling Regime
The Atomic-Cooling Stage
THE EPOCH OF IONIZATION BREAKTHROUGH
UV Production in `Subgalaxies'
How Uncertain is the Ionization Epoch?
Detecting `Pregalaxies' at Very High Redshift
The `Breakthrough' Epoch
Black Hole Formation and AGNs at High z?
Distinguishing Between Objects with z >
zi and z < zi
RADIO AND MICROWAVE PROBES OF THE IONIZATION
EPOCH
CMB Fluctuations as a Probe of the Ionization
Epoch
21 cm Emission, Absorption and Tomography
VERY DISTANT SUPERNOVAE (AND PERHAPS GAMMA-RAY
BURSTS)
The Supernova Rate at High Redshifts
Gamma Ray Bursts: The Most Luminous Known Cosmic
Objects
WHERE ARE THE OLDEST (AND THE EXTREME METAL-POOR)
STARS?
SUMMARY
REFERENCES
