Newly Discovered Bright z ∼ 9–10 Galaxies and Improved Constraints on Their Prevalence Using the Full CANDELS Area

Abstract

We report the results of an expanded search for z  ∼ 9–10 candidates over the ∼883 arcmin 2 CANDELS+ERS fields. This study adds 147 arcmin 2 to the search area we consider over the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS) COSMOS, UDS, and EGS fields, while expanding our selection to include sources with bluer J 125  −  H 160 colors than our previous J 125  −  H 160  > 0.5 mag selection. In searching for new z  ∼ 9–10 candidates, we make full use of all available Hubble Space Telescope ( HST ), Spitzer /IRAC, and ground-based imaging data. As a result of our expanded search and use of broader color criteria, three new candidate z  ∼ 9–10 galaxies are identified. We also find again the z  = 8.683 source previously confirmed by Zitrin et al. This brings our sample of probable z  ∼ 9–11 galaxy candidates over the CANDELS+ERS fields to 19 sources in total, equivalent to one candidate per 47 arcmin 2 (one per 10 WFC3/IR fields). To be comprehensive, we also discuss 28 mostly lower likelihood z  ∼ 9–10 candidates, including some sources that seem to be reliably at z  > 8 using the HST +IRAC data alone, but which the ground-based data show are much more likely at z  < 4. One case example is a bright z  ∼ 9.4 candidate, COS910-8, which seems instead to be at z  ∼ 2. Based on this expanded sample, we obtain a more robust luminosity function (LF) at z  ∼ 9 and improved constraints on the volume density of bright z  ∼ 9 and z  ∼ 10 galaxies. Our improved z  ∼ 9–10 results again reinforce previous findings for strong evolution in the UV LF at z  > 8, with a factor of ∼10 evolution seen in the luminosity density from z  ∼ 10 to z  ∼ 8.