JADES Dark Horse: demonstrating high-multiplex observations with JWST /NIRSpec dense-shutter spectroscopy in the JADES Origins Field

Journal article

We present James Web Space Telescope/NIRSpec dense-shutter spectroscopy (DSS). This novel observing strategy with the NIRSpec/multi-shutter assembly (MSA) deliberately permits a high number of controlled spectral overlaps to reach extreme multiplex while retaining the low background of slit spectroscopy. In a single configuration over the JADES Origins Field, we opened shutters on all faint ( mag) candidates, prioritizing emission-line science and rejecting only bright continuum sources. Using 33.6 and 35.8 ks on-source in G235M and G395M, we observed a single mask with 850 sources, obtaining spectroscopic redshifts for 540 galaxies over . The per-configuration target density in DSS mode is 4–5 higher than standard no- and low-overlap MSA strategies (<200 sources), with no loss in redshift precision or accuracy. Line-flux sensitivities are 30 per cent lower at fixed exposure time, matching the expected increase in background noise, but the gain in survey speed is 5 in our setup, more than justifying the penalty. The measured line sensitivity exceeds NIRCam slitless spectroscopy by at least ( in exposure time) at , demonstrating that DSS is a compelling method to gain deep, wide-band spectra for large samples. Crucially, NIRSpec/MSA could deliver even higher target allocation densities than those used here. We derive H α-based star-formation rates, gas-phase metallicities (including a large sample suitable for strong-line calibrations), and identify rare mini-quenched galaxies and broad-line AGN. DSS is immediately applicable wherever deep imaging enables robust pre-selection and astrometry, providing an efficient method to obtain large samples of faint emission-line galaxies, a compelling middle ground between the completeness of slitless surveys and the sensitivity and bandwidth of NIRSpec/MSA.

Authors: D’Eugenio, F; Nelson, EJ; Eisenstein, DJ; Maiolino, R; Carniani, S

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: Monthly Notices of the Royal Astronomical Society
• Volume: 549
• Issue: 2
• Pages: stag824
• Article number: stag824
• Publication date: 2026-04-30
• Acceptance date: 2026-04-02
• DOI: 10.1093/mnras/stag824
• EISSN: 1365-2966
• ISSN: 0035-8711
• Language: English
• Keywords: techniques: spectroscopic; galaxies: ISM; galaxies: high-redshift; methods: observational; surveys; instrumentation: spectrographs