Kavli Affiliate: Roberto Maiolino
| First 5 Authors: Francesco D’Eugenio, Francesco D’Eugenio, , ,
| Summary:
We present JWST/NIRSpec dense-shutter spectroscopy (DSS). This novel
observing strategy with the NIRSpec micro-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
(F444W<30 mag) z$_rm phot$>3 candidates in the MSA, prioritising
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 secure spectroscopic redshifts for ~540 galaxies over
2.5<z<8.9. The per-configuration target density in DSS mode is 4-5x higher than
standard no- and low-overlap MSA strategies (<200 sources), with no loss in
redshift precision or accuracy. Line-flux sensitivities are 30 percent lower at
fixed exposure time, matching the expected increase in background noise, but
the gain in survey speed is 5x in our setup, more than justifying the penalty.
The measured line sensitivity exceeds NIRCam WFSS by a minimum factor of ~5
(i.e. ~25 in exposure time) at $lambda$~4 $mu$m, demonstrating that
controlled overlap is a compelling method to gain deep, wide-band spectra for
large samples. Crucially, we envisage the MSA could deliver even higher target
allocation densities than what used here. We derive Balmer-line based SFRs,
gas-phase metallicities (including a large sample suitable for strong-line
calibrations), and identify rare sources (mini-quenched systems and broad-line
AGN). This approach 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.
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