Bryn Mawr College Physics Colloquium
and Class of 1902 Lecture

Let there be Light: The Quest for the First Galaxies

Richard Ellis
Steele Professor of Astronomy
Monday 3 February 2014


Abstract: 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 responsible? 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 uncharted period holds the key to addressing these fundamental questions.  Recent 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 future facilities such as TMT and JWST.