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

ABSTRACT 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 ($m_\mathrm{F444W}\lt 30$ mag) $z_{\rm phot}\gt 3$ 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 $\sim$850 sources, obtaining spectroscopic redshifts for $\sim$540 galaxies over $2.5\lesssim z \lesssim 8.9$. The per-configuration target density in DSS mode is 4–5$\times$ higher than standard no- and low-overlap MSA strategies (