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J. Hewitt (MIT )
The most distant structure we observe is the surface of last scattering of the cosmic microwave background, marking recombination at a redshift of about 1000. The next most distant structures we observe are quasars and galaxies at a redshift of about 6, collapsed objects whose spectra tell us the universe is reionized at that redshift. Between redshifts of 1000 and 6, the neutral hydrogen must have formed the first structures with the dark matter, formed the first luminous objects, and undergone reionization. Optical spectra of the highest redshift quasars show intriguing features that may be evidence for the process of reionization. The signatures of reheating and reionization may also be observable in the redshifted 21cm line of neutral hydrogen. One of the goals of the planned low frequency array LOFAR is to detect these signatures.
This work was supported by a grant from the National Science Foundation.