Galaxies at High Redshift and Reionization
  The quest to discover the most distant galaxies has developed rapidly in the
last decade. We are now exploring redshifts of 6 and beyond, when the Universe
was less than a billion years old, an epoch when the previously-neutral
intergalactic medium was reionized. The continuing discovery of galaxies at
progressively higher and higher redshifts has been driven by the availability
of large telescopes on the ground and in space, improvements in detector
technology, and new search strategies. Over the past 4 years, the Lyman break
technique has been shown to be effective in isolating z~6 star-forming i'-drop
galaxies through spectroscopic confirmation with large ground-based telescopes
(Keck, Gemini and the ESO VLTs). Narrow-band imaging, notably with the wide
field of the Subaru telescope, has also produced samples of Lyman-alpha
emitters at these redshifts. A The discovery of this i'-drop galaxy population
has been used to infer the global star formation rate density at this epoch
(z~6), and we are now beginning to constrain the contribution to reionization
of the UV flux from these galaxies. Infrared data from the Spitzer Space
Telescope has been used to determine the spectral energy distributions (SEDs)
from the rest-frame UV to the optical, and constrain the previous star
formation histories, masses and ages. The indications are that much of the
stellar mass of these galaxies might have formed in vigorous bursts at z>6. The
next big advances would be to test the population synthesis modelling of these
z~6 galaxies through spectroscopy of the rest-frame optical (rather than crude
broad-band SEDs), and also to push the observational horizon for galaxies
further to directly explore star formation during the reionization epoch. JWST
is likely to have a profound impact on realising these goals.
