Cosmology with 21-cm Radio Observations Rennan Barkana, Moore Distinguished Scholar, Caltech Senior Lecturer, Department of Physics and Astronomy, Tel Aviv University

Cosmologists have studied on the one hand the cosmic microwave background from the early universe, and on the other hand, galaxies and quasars that formed much more recently. This leaves an unknown frontier, from redshift 6 up to 1000, during which the first stars formed and subsequently heated and ionized the cosmic gas. Several international efforts are underway to measure the redshifted emission from the resonance line at a wavelength of 21 cm of hydrogen atoms at early cosmic times. This new observational tool promises to become a major probe of early cosmic history.