Observational Signatures of the First Luminous Objects

The next generation of astronomical instruments will be able to detect dense pockets of ionized gas created by the first luminous objects. The integrated free-free emission from ionized halos creates a spectral distortion of the Cosmic Microwave Background, greater than the distortion due to the reionized intergalactic medium. Its detection is well within the capabilities of the planned DIMES satellite. Ionized halos may also be imaged directly in free-free emission by the Square Kilometer Array. Bright halos will be detected as discrete sources, while residual unresolved sources can still be detected statistically from temperature fluctuations in maps. Balmer line emission from ionized halos is detectable by the Next Generation Space Telescope and can be used to obtain redshift information. Unlike Ly-alpha, the H-alpha line does not suffer from resonant scattering by neutral hydrogen, and is still observable when the IGM is not fully reionized. In addition, it is less susceptible to dust extinction. Finally, the kinetic Sunyaev-Zeldovich effect may be used to detect ionized gas at high redshift. Used in concert, these observations will probe ionizing emissivity, gas clumping, and star formation in the early universe.