| This thesis focuses on the epoch 5 < z < 40 when the first luminous objects in the universe formed and reionized the intergalactic medium (IGM). I have paid particular attention to observational signatures of these objects with present or upcoming instruments such as the Square Kilometer Array (SKA), Next Generation Space Telescope (NGST), Chandra X-ray Observatory (CXO), and Gamma-Ray Large Area Space Telescope (GLAST).; The first supernovae which polluted the IGM with metals seen at lower redshifts also accelerated relativistic electrons. CMB photons can inverse-Compton scatter off these electrons, producing X-rays. Unlike UV photons, these X-rays can escape easily from their host to reionize the universe. Their large mean free path implies that the universe could have been reionized in a homogeneous manner, rather than as a two-phase medium. Furthermore, these photons can inject energy via HeII ionizations to heat the IGM to high temperatures. X-rays also increase the electron fraction in the IGM, promoting gas-phase H 2 formation and cooling.; The first ionizing sources should be visible in free-free emission with the SKA. In addition, NGST should be able to detect Balmer-line emission and obtain redshift measurements. Unlike Lyalpha emission, Halpha emission is unattenuated by resonant scattering in the neutral IGM. X-ray emission from the first star clusters is unlikely to be directly observable by CXO, though the integrated emission could constitute a significant fraction of the remaining unresolved X-ray background. Using synchrotron emission measurements with the SKA, one can test for the presence of relativistic electrons and infer the level of X-ray emission. Finally, high-redshift blazars may be detectable with GLAST. Observations of gamma-ray absorption due to pair production against high-redshift UV photons can constrain UV radiation fields and star formation during the reionization epoch. |
