Galaxies at Cosmic Dawn: Exploring the First Billion Years with Hubble and Spitzer – Implications for JWST

Wed 02 Aug, 2017 @12PM, level 7
Prof. Garth Illingworth, Professor
University of California Santa Cruz
Email: gedi[at]


Hubble has revolutionized the discovery and study of very distant galaxies through its deep imaging surveys. Together the HST WFC3/IR and ACS cameras have opened up the exploration of the universe in the first billion years after the Big Bang. I will discuss what we have learned about the earliest galaxies during the reionization epoch at z>6 from the remarkable HST and Spitzer imaging surveys (e.g., HUDF/XDF, GOODS, HUDF09/12 and CANDELS), as well as surveys of galaxy clusters like the Frontier Fields (HFF). Lensing clusters provide extraordinary opportunities for characterizing the faintest earliest galaxies, but also present extraordinary challenges. Together these surveys have reliably established the volume density of galaxies in the first billion years down to extremely faint levels around -14.5 mag. The results from deep UV luminosity functions from Hubble, combined with the recent results from Planck, indicate that galaxies dominate the UV ionizing flux that reionized the universe. Some of the greatest surprises have come from the discovery of very luminous galaxies at z~8-11, around 400-650 million years after the Big Bang. Spectroscopic followup of these very rare, bright galaxies has confirmed redshifts from z~7 to z~11, and revealed, surprisingly, strong Ly╬▒ emission near the peak of reionization when the HI fraction in the IGM is high. The small sizes of galaxies at high redshifts, from analysis of the HFF cluster samples, reveal objects that, remarkably, are as small as globular clusters and dwarf galaxies. The recent confirmation of a z=11.1 galaxy, just 400 million years after the Big Bang, by a combination of Hubble and Spitzer data, pushed Hubble into JWST territory, far beyond what we ever expected Hubble could do. Twenty years of astonishing progress with Hubble and Spitzer leave me looking to JWST to provide even more remarkable exploration of the realm of the first galaxies at “Cosmic Sunrise”. The latest results on the sizes of distant galaxies, on the star formation rate density at z~10 and from Planck indicating that reionization began around z~10 together have significant implications for the detectability of the “first galaxies” with JWST.