Observable Signatures of Reionization

Harvard University, Cambridge MA

Investigators

Abstract

AST 0204514 Loeb According to the most current theories of cosmology, hydrogen, the most abundant element left over from the big bang, was formed out of free electrons and protons when the Universe cooled below a temperature of a few thousand degrees. However, recent observations imply that most of this relic cosmic hydrogen was dissociated once again (i.e., `re-ionized') less than a billion years after the big bang. It is commonly believed that the cosmic hydrogen was re-ionized by the ultraviolet radiation emitted by the first generation of stars and black holes in the universe. How and when did the first galaxies form in the Universe? What was their effect on the surrounding cosmic gas? These are two of the most exciting questions in observational and theoretical cosmology today. This project will combine analytic calculations and limited numerical simulations of radiative transfer problems to address these questions and make detailed predictions for the expected clues that future, cutting-edge observations might reveal. In particular, it will identify observational probes that could signal the cosmic time at which most of the hydrogen was re-ionized. The interplay between theory and observations of the hydrogen re-ionization epoch will constrain the properties of the first sources of light in the early Universe as well as fundamental cosmological parameters (including the nature of the dark matter). ***