Schedule Feb 17, 2012
The z~10 Universe Explored with HST
Pascal Oesch (UCSC, UCO)

Thanks to the installation of WFC3/IR on-board the HST, great progress has been made in exploring the galaxy population at z~7-8, in the heart of cosmic reionization, where more than 100 galaxy candidates have now been identified. These detections have enabled a detailed quantification of the evolution of the UV luminosity function (LF) of galaxies out to z~8. Pushing to even higher redshifts has proven to be extremely difficult due to the intrinsic faintness of these primordial galaxies and due to the strong absorption by the neutral intergalactic medium, which renders such galaxies invisible shortward of ~1.2 μm. Here we present a search for z~10 galaxies over ~160 arcmin2 of WFC3/IR data in the Chandra Deep Field South (CDFS). We use public data obtained with the HUDF09, ERS and CANDELS surveys and combine it with ancillary optical ACS imaging as well as with newly acquired Spitzer IRAC data from the IUDF10 program. We performed an independent analysis, tripling the search area at all luminosities relative to our first z~10 search (presented in Bouwens et al. 2011). After removing 15 intermediate redshift contaminants with strong IRAC detections, we only find one plausible z~10 candidate, that we previously reported on. The dearth of z~10 candidates indicates that the UV luminosity density increases by more than an order of magnitude in only 170 Myr from z~10 to z~8. This is a factor >4x larger than expected from an extrapolation of the empirical trends of the UV LF parameters with redshift. We are thus likely witnessing the first rapid build-up of galaxies at this epoch.


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