PROBING THE COSMIC DARK AGES USING THE 21 CM LINE Jonathan Pritchard California Institute of Technology, Pasadena, CA, USA
Observations of the redshifted 21 cm line offer a promising probe of the intergalactic medium (IGM) before reionization is completed. Anisotropies in the 21 cm signal arise from ﬂuctuations in the IGM temperature, density, and neutral fraction and through the Lyman alpha ﬂux. These ﬂuctuations contain a wealth of information about astrophysics and cosmology. At lower redshifts (z < 30), the state of the IGM is determined by the nature and number of luminous sources. In this regime, 21 cm observations should shed light on the thermal history of the IGM and how reionization proceeds. At higher redshifts (30 < z < 200), it may be possible to probe truly primordial gas and make precision measurements of the D-H ratio. Additionally, if the matter power spectrum can be extracted from the signal, measurements of cosmological parameters can be made. In this talk, I discuss the theory underlying 21 cm observations and explore many of these possible applications.