The BoRG-JWST Survey: Program Overview and First Confirmations of Luminous Reionization-era Galaxies from Pure-parallel Observations
April 2025 • 2025ApJ...983...18R
Abstract • We present the BoRG-JWST survey, a combination of two JWST Cycle 1 programs aimed at obtaining NIRSpec spectroscopy of representative, UV-bright 7 < z < 10 galaxy candidates across 22 independent sight lines selected from Hubble/WFC3 pure-parallel observations. We confirm the high-z nature of 12 out of 21 observed primary targets through low-resolution prism observations, with the rest revealing themselves unsurprisingly to be z ∼ 1–3 interlopers, brown dwarfs, or yielding inconclusive results. From the Multi Shutter Array (MSA) observations, we confirm an additional nine filler sources at z > 5, highlighting the large abundance of high-redshift galaxies even in individual WFC3 pointings. The primary sample spans the absolute magnitude range ‑20.4 mag < MUV < ‑22.4 mag and harbors UV continuum slopes of β ≃ ‑2.5 to ‑2.0, representing some of the most luminous z > 7 sources currently known and comparable to the brightest NIRCam sources at z > 10. Prominent [O III]+Hβ lines are found across the full sample, while a stack of sources reveals a plethora of other rest-optical lines and additional rest-UV C III] 1909 Å emission. Despite their luminosities, none of the low-resolution spectra display evidence for type 1 active galactic nucleus activity based on a search for broad-line emission. Lastly, we present a spectroscopic data release of 188 confirmed 0.5 ≲ z ≲ 5.0 sources from filler MSA observations, highlighting the legacy value of the survey and a representative benchmark for comparisons to deep field observations.
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