The Brightest $z\gtrsim8$ Galaxies over the COSMOS UltraVISTA Field

Understand

We present 16 new ultrabright $H_{AB}\lesssim25$ galaxy candidates at z~8 identified over the COSMOS/UltraVISTA field.

• The new search takes advantage of the deepest-available ground-based optical and near-infrared observations, including the DR3 release of UltraVISTA and full-depth Spitzer/IRAC observations from the SMUVS and SPLASH programs.
• Candidates are selected using Lyman-break criteria, combined with strict optical non-detection and SED-fitting criteria, minimizing contamination by low-redshift galaxies and low-mass stars.
• HST/WFC3 coverage from the DASH program reveals that one source evident in our ground-based near-IR data has significant substructure and may actually correspond to 3 separate z~8 objects, resulting in a sample of 18 galaxies, 10 of which seem to be fairly robust (with a >97% probability of being at z>7).