The BoRG-JWST Survey: Program Overview and First Confirmations of Luminous Reionization-Era Galaxies from Pure-Parallel Observations

TL;DR

The BoRG-JWST survey confirms the existence of luminous reionization-era galaxies at redshifts 7-10, providing spectroscopic data and revealing their properties, including strong emission lines and absence of AGN activity, across multiple sight lines.

Contribution

This study presents the first spectroscopic confirmations of luminous $z>7$ galaxies from JWST pure-parallel observations, expanding knowledge of early universe galaxy populations.

Findings

Confirmed 10 high-$z$ galaxies out of 19 targets.

Detected prominent rest-optical emission lines across the sample.

Provided a large spectroscopic dataset of 188 sources from filler observations.

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 10 out of 19 observed primary targets through low-resolution prism observations, with the rest revealing themselves unsurprisingly to be $z\sim1-3$ interlopers, brown dwarfs, or yielding inconclusive results. From the MSA observations, we confirm an additional 9 filler sources at $z>5$, highlighting the large abundance of high-redshift galaxies even in individual WFC3 pointings. The primary sample span an absolute magnitude range $-20.4<M_{\rm UV}<-22.4$ mag and harbour UV continuum slopes of $\beta\simeq-2.5$ to $-2.0$, representing some of the most luminous $z>7$ sources currently known and comparable to the brightest sources at $z>10$. Prominent [O III]+H$\beta$ 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 \r{A} emission. Despite their luminosities, none of the low-resolution spectra display evidence for Type 1 AGN activity based on a search for broad-line emission. Lastly, we present a spectroscopic data release of 188 confirmed $0.5\lesssim z\lesssim5.0$ sources from filler MSA observations, highlighting the legacy value of the survey and a representative benchmark for comparisons to deep field observations.