Probing the Dawn of Galaxies at z ~ 9-12: New Constraints from HUDF12/XDF and CANDELS data

Abstract

We present a comprehensive analysis of z {gt} 8 galaxies based on ultra-deep WFC3/IR data. We exploit all the WFC3/IR imaging over the Hubble Ultra-Deep Field from the HUDF09 and the new HUDF12 program, in addition to the HUDF09 parallel field data, as well as wider area imaging over GOODS-South. Galaxies are selected based on the Lyman break technique in three samples centered around z ~{} 9, z ~{} 10, and z ~{} 11, with seven z ~{} 9 galaxy candidates, and one each at z ~{} 10 and z ~{} 11. We confirm a new z ~{} 10 candidate (with z = 9.8 {plusmn} 0.6) that was not convincingly identified in our first z ~{} 10 sample. Using these candidates, we perform one of the first estimates of the z ~{} 9 UV luminosity function (LF) and improve our previous constraints at z ~{} 10. Extrapolating the lower redshift UV LF evolution should have revealed 17 z ~{} 9 and 9 z ~{} 10 sources, i.e., a factor ~{}3 { imes} and 9{ imes} larger than observed. The inferred star formation rate density (SFRD) in galaxies above 0.7 M $_{⊙}$ yr$^{-1}$ decreases by 0.6 {plusmn} 0.2 dex from z ~{} 8 to z ~{} 9, in excellent agreement with previous estimates. From a combination of all current measurements, we find a best estimate of a factor 10{ imes} decrease in the SFRD from z ~{} 8 to z ~{} 10, following (1 + z)$^{-11.4 ± 3.1}$. Our measurements thus confirm our previous finding of an accelerated evolution beyond z ~{} 8, and signify a very rapid build-up of galaxies with M $_{UV}$ {lt} -17.7 mag within only ~{}200 Myr from z ~{} 10 to z ~{} 8, in the heart of cosmic reionization. Based on data obtained with the Hubble Space Telescope operated by AURA, Inc., for NASA under contract NAS5-26555.