Bright Galaxies at Hubble’s Redshift Detection Frontier: Preliminary Results and Design from the Redshift z ~ 9-10 BoRG Pure-Parallel HST Survey

We present the first results and design from the redshift z ∼ 9-10 Brightest of the Reionizing Galaxies Hubble Space Telescope survey BoRG[z9-10], aimed at searching for intrinsically luminous unlensed galaxies during the first 700 Myr after the Big Bang. BoRG[z9-10] is the continuation of a multi-year pure-parallel near-IR and optical imaging campaign with the Wide Field Camera 3. The ongoing survey uses five filters, optimized for detecting the most distant objects and offering continuous wavelength coverage from λ = 0.35 μm to λ = 1.7 μm. We analyze the initial ∼130 arcmin² of area over 28 independent lines of sight (∼25% of the total planned) to search for z\gt 7 galaxies using a combination of Lyman-break and photometric redshift selections. From an effective comoving volume of (5-25) × 10⁵ Mpc³ for magnitudes brighter than {m}_{AB}=26.5{{{--}}}24.0 in the {H}_{{160}}-band respectively, we find five galaxy candidates at z\quad ∼ 8.3-10 detected at high confidence ({{S}}/{{N}}\gt 8), including a source at z\quad ∼ 8.4 with {m}_{AB}=24.5 ({{S}}/{{N}} ∼ 22), which, if confirmed, would be the brightest galaxy identified at such early times (z\gt 8). In addition, BoRG[z9-10] data yield four galaxies with 7.3≲ z≲ 8. These new Lyman-break galaxies with m≲ 26.5 are ideal targets for follow-up observations from ground and space-based observatories to help investigate the complex interplay between dark matter growth, galaxy assembly, and reionization.