Sep 27, 2012
Dan Stark, University of Arizona
"Early Star Forming Galaxies and the Reionization of the Universe"
The events of the first billion years of cosmic history are one of the final frontiers in the quest to trace the history of the Universe from its origins to the present day. Exploration of this uncharted era is driven by the desire to locate and understand the nature of the first stars and galaxies and to characterize their contribution to the reionization of hydrogen. With the installation of the Wide Field Camera 3 (WFC3) onboard the Hubble Space Telescope, the cosmic frontier has been pushed back to just 500 Myr after the Big Bang, delivering the first census of star formation activity in the reionization era. Deep spectroscopy of these early systems is now providing insight into the properties of primitive galaxies while simultaneously constraining the progress of reionization. I will summarize the results from these studies, providing tentative evidence that reionization comes to an end between z~7 and z~6, while revealing some tension in the ability of star-forming galaxies to achieve reionization by z=6. Finally I will discuss how spectroscopic studies of low mass gravitationally- lensed galaxies at moderate and high redshift are improving our understanding of the formation of early galactic systems, hinting at an increased transmission of ionizing radiation into the intergalactic medium and a harder ionizing spectrum.