Cosmological Reionization and the End of the Dark Ages

Paul Shapiro, University of Texas

The universe was reionized by redshift z ~ 6 by a small fraction of the baryons in the universe, which released energy following their condensation out of a cold, dark, and neutral IGM into the earliest galaxies. The theory of this reionization is a critical missing link in the theory of galaxy formation. Its numerous observable consequences include effects on the spectrum, anisotropy and polarization of the cosmic microwave background and signatures of high-redshift star and quasar formation. This energy release also created feedback on galaxy formation which left its imprint on the mass spectrum and internal characteristics of galaxies and on the gas between galaxies long after reionization was complete. Recent work suggests that the photoevaporation of dwarf galaxy minihalos may have consumed most of the photons required to reionize the currently-favored Lambda-CDM universe. We will review recent developments in our understanding of this process, in the context of the recent discovery of angular fluctuations in the polarization of the CMB at large angles by WMAP and the detection of the Gunn-Peterson effect in the spectra of high redshift quasars at z ~ 6 discovered by the Sloan Digital Sky Survey. We will also discuss the possibility of observing redshifted 21-cm lines from these minihalos before and during reionization, the first baryonic structures to emerge in the universe.