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Observations of Star Forming Galaxies in the Heart of the Reionization Era

Colloquium: Astronomy Colloquia | April 3 | 4:10 p.m. | 1 LeConte Hall

Richard Ellis, Caltech

Department of Astronomy

Deep exposures with the Hubble Space Telescope (HST) have provided the primary evidence that star-forming galaxies were present in the first billion years of cosmic history. Sometime during this early period the intergalactic medium transitioned from a neutral gas to one that is fully ionized. How did this 'cosmic reionization' occur and were star-forming galaxies the primary agents? The electron scattering optical depth inferred from cosmic microwave background observations suggests that reionization occurred sometime in the redshift interval z = 20 to z = 6 so probing the abundance, luminosity distribution and spectral properties of galaxies during this period holds the key to addressing these fundamental questions. Imaging with HST's Wide Field Camera 3 in conjunction with Spitzer photometry and Keck spectroscopy has provided important new insight into understanding when reionization occurred and the role of early galaxies in the process. I will review this progress and discuss the remaining challenges ahead of plans for future facilities such as TMT and JWST., 510-642-5275