Dr. Pascal Oesch Space Telescope Science Institute

Thanks to ultra-deep observations with the WFC3/IR camera on Hubble the frontier of galaxies has recently been pushed out to z~9-12, only ~450 Myr from the Big Bang. From several large Hubble programs such as the HUDF09, CANDELS, or CLASH, we were able to identify large samples of more than 200 galaxies at z~7-8, and we are now starting to build up the sample sizes of z~9-11 galaxy candidates. In particular, the recent HUDF12 campaign further increased the depth of the WFC3/IR dataset over the Hubble Ultra-Deep Field (HUDF), and enabled us to detect a sample of nine very faint z>8 galaxy candidates in the HUDF. Additionally, the newly completed CANDELS data over GOODS-North now revealed four relatively bright z~9-10 sources, which are in tension with the previous UV LF determination from the GOODS-South field, indicating that star-formation in the early universe might have been very stochastic. Using all z>8 candidates in and around both GOODS fields, we infer that the cosmic star-formation rate density in galaxies with SFR>0.7Msol/yr decreases rapidly at z>8, dropping by an order of magnitude from z~8 to z~10. With complementing, ultra-deep Spitzer IRAC data, we are additionally able to infer the stellar mass densities out to z~8-10. In this talk I will highlight recent progress in exploring the high redshift frontier and in understanding the growth of galaxies in the first two billion years. In particular, I will present current constraints on the UV luminosity function of galaxies at z>8, and I will demonstrate the power of combining deep Hubble and Spitzer data to directly track the star-formation and mass build-up of z>=4 galaxies.