JWST-SUSPENSE Survey: Dual Phase Cosmic Study

• JWST-SUSPENSE Survey is a dual-purpose JWST program that unifies a time-domain search for reionization-era transients with an ultradeep spectroscopic study of quiescent galaxies at cosmic noon.
• It employs NIRCam imaging alongside NIRISS and targeted NIRSpec follow-up to capture high-redshift phenomena such as Pop III supernovae, direct collapse black holes, and cosmic infrared background fluctuations.
• The survey’s spectroscopic arm uses NIRSpec/MSA to derive detailed stellar populations, chemical abundances, and kinematics, offering new insights into galaxy formation and quenching.

JWST-SUSPENSE denotes two distinct survey constructs in the JWST literature that share a common emphasis on exploiting JWST sensitivity for problems inaccessible to pre-JWST facilities. In the ASTRO2020 white paper literature, the “JWST-SUSPENSE Survey” is a proposed public, deep-and-wide time-domain program using NIRCam, NIRISS, and targeted NIRSpec follow-up to probe the epoch of reionization, discover the earliest black holes and supernovae, and measure cosmic infrared background fluctuations at $2\!-\!5\,\mu\mathrm{m}$ (Wang et al., 2019). In later GO-2110 usage, “JWST-SUSPENSE” expands to the Spectroscopic Ultradeep Survey Probing Extragalactic Near-infrared Stellar Emission, an ultra-deep NIRSpec/Micro-Shutter Array program targeting massive quiescent galaxies at $1star-formation histories, elemental abundances, spatial gradients, and stellar kinematics during cosmic noon (Slob et al., 2024). The shared name has therefore come to encompass both a high-redshift time-domain survey concept and a realized ultradeep spectroscopic survey.

1. Nomenclature and survey family

The literature uses “JWST-SUSPENSE” in two technically different senses. The first is a wide-field, time-domain survey concept framed around the epoch of reionization and the Dark Ages, with primary science centered on Pop III supernovae, direct collapse black holes, superluminous supernovae, SN Ia cosmology to high redshift, and source-subtracted cosmic infrared background fluctuations (Wang et al., 2019). The second is a spectroscopic program executed with NIRSpec/MSA, explicitly designed to characterize the stellar, chemical, and kinematic properties of massive quiescent galaxies at cosmic noon (Slob et al., 2024).

Usage	Primary science	Core configuration
JWST-SUSPENSE Survey	Epoch of reionization, transients, CIB fluctuations	NIRCam imaging at $2\!-\!5\,\mu\mathrm{m}$, NIRISS parallel slitless spectroscopy, targeted NIRSpec follow-up
JWST-SUSPENSE Ultradeep Spectroscopic Program	Quiescent galaxies at $1	NIRSpec/MSA, G140M/F100LP, ultra-deep spectroscopy

This dual usage is not merely terminological. The time-domain concept is a proposed community survey architecture, whereas the ultradeep spectroscopic program is an implemented observing program, GO-2110. A common misconception is that JWST-SUSPENSE refers to a single homogeneous survey. The published record instead supports a broader “survey family” interpretation: the name links distinct JWST observing strategies unified by ambitious use of near-infrared sensitivity, but applied to different redshift regimes, source classes, and inference problems.

2. The wide-field time-domain concept for reionization-era science

In the ASTRO2020 white paper, JWST-SUSPENSE is conceived as a public, deep-and-wide time-domain program intended to deliver the baseline dataset required to probe reionization at $z>6$ and potentially out to $z\sim20\!-\!30$ (Wang et al., 2019). Its prime targets are the earliest compact objects and explosive transients: direct collapse black hole seeds, the first supernovae—including core-collapse, pair-instability, and superluminous events—and the collective emission traced through cosmic infrared background fluctuations. The same survey is also proposed as an enabling dataset for supernova cosmology to $z\sim5\!-\!6$, high-redshift star-formation history through supernova explosions, galaxy evolution to $z\sim10$, and faint stellar populations in the Milky Way.

The proposed science case is built around JWST sensitivity in the $2\!-\!5\,\mu\mathrm{m}$ window, where high-redshift rest-frame UV–optical emission is shifted into the near-IR according to

$\lambda_{\rm obs}=(1+z)\lambda_{\rm rest}.$

Time dilation is central to the survey logic: $1Wang et al., 2019).

The paper also specifies astrophysical source classes. Pair-instability supernovae from non-rotating Pop III progenitors at $1al. (2019) are quoted as estimating $2\!-\!5\,\mu\mathrm{m}$0 Pop III SNe in $2\!-\!5\,\mu\mathrm{m}$1 over 5 years at $2\!-\!5\,\mu\mathrm{m}$2 for a $2\!-\!5\,\mu\mathrm{m}$3 survey reaching 26.5 AB mag; the white paper argues that deeper, redder $2\!-\!5\,\mu\mathrm{m}$4 coverage should improve discovery prospects (Wang et al., 2019).

For black-hole seed science, direct collapse black holes are expected in atomically cooled halos at $2\!-\!5\,\mu\mathrm{m}$5 and are described as potentially bright enough for JWST detection to $2\!-\!5\,\mu\mathrm{m}$6. Their comparatively low masses and accretion states are presented as a specific motivation for time-domain discovery, since variability is expected to be more likely than in massive quasars. For superluminous supernovae, the white paper distinguishes hydrogen-rich SLSN II, powered by ejecta–CSM collisions, and hydrogen-poor SLSN I, described as magnetar-powered. These are stated to be $2\!-\!5\,\mu\mathrm{m}$7 mag brighter than SNe Ia and at least 4 mag brighter than common core-collapse SNe, with UV-bright rest-frame SEDs implying detectability to $2\!-\!5\,\mu\mathrm{m}$8 in JWST near/mid-IR bands (Wang et al., 2019).

3. Survey design of the time-domain program

The proposed time-domain implementation centers on NIRCam imaging between 2 and $2\!-\!5\,\mu\mathrm{m}$9, with NIRISS slitless spectroscopy obtained in parallel and deeper targeted NIRSpec follow-up for key objects (Wang et al., 2019). The white paper identifies F150W2 and F322W2 as the primary filters because they provide wide color baselines with high sensitivity, while F200W and F444W add 2 and $1anchor points. Multi-color coverage is required both for transient classification and for cosmic infrared background tomography using adjacent-band differencing.

Field selection is driven by the need for continuous time-domain coverage. Continuous Viewing Zones are described as mandatory. The northern CVZ contains an established community field of $1SKA. The southern CVZ’s proximity to the LMC is said to be acceptable for transients but potentially problematic for CIB studies, motivating a geometry in which southern survey area can be split into subareas straddling the CVZ to reduce cirrus contamination (Wang et al., 2019).

The cadence strategy is explicitly two-tiered. A core field of $1Wang et al., 2019).

Single-epoch depth targets are also specified. Per epoch, the survey aims for AB $1$z>6$0 in F200W and F444W. Approximate $z>6$1 limits are then quoted as $z>6$2 for the bands with $z>6$3 at 27 AB mag, and $z>6$4 for those with $z>6$5 at 27 AB mag. The survey planning uses the standard AB definition

$z>6$6

the flux–luminosity relation

$z>6$7

and a single-epoch signal-to-noise model

$z>6$8

with $z>6$9 the source counts, $z\sim20\!-\!30$0 the total background, and $z\sim20\!-\!30$1 the effective read noise. Coadding $z\sim20\!-\!30$2 identical epochs raises $z\sim20\!-\!30$3 by $z\sim20\!-\!30$4 (Wang et al., 2019).

The quoted time allocation is $z\sim20\!-\!30$5 hours per year for $z\sim20\!-\!30$6 in four filters at the stated depths. Illustrative configurations include $z\sim20\!-\!30$7 hours per year for a $z\sim20\!-\!30$8 survey with 180-day cadence, and $z\sim20\!-\!30$9 hours per year for a $z\sim5\!-\!6$0 survey with 90-day cadence. Parallel observing is built into the design to maximize return (Wang et al., 2019).

4. Cosmic infrared background science and quantitative framework

A defining feature of the time-domain SUSPENSE concept is that it treats unresolved high-redshift populations not only as individual transient targets but also as a collective background signal. The white paper states that source-subtracted CIB fluctuations at $z\sim5\!-\!6$1 had already been detected by Spitzer and AKARI, and proposes JWST/NIRCam imaging plus aggressive masking of known galaxies to $z\sim5\!-\!6$2 AB mag across $z\sim5\!-\!6$3 in order to measure the angular power spectrum of the residual fluctuations (Wang et al., 2019).

The measurement strategy is highly specific. It requires multi-epoch maps with uniform coverage and strong artifact rejection, source detection and masking to at least 28 AB mag to suppress shot noise from known galaxies, accurate beam and PSF characterization, cross-band registration, and power-spectrum estimation over wide angular scales with corrections for mask-induced mode coupling and instrument noise. Adjacent-band differencing is used for Lyman-break tomography, isolating redshift slices through the spectral discontinuity at the Lyman limit or break. The white paper states that this can constrain the redshift history of emission over $z\sim5\!-\!6$4 as the Universe emerges from the Dark Ages (Wang et al., 2019).

The formalism is standard but explicit. The comoving volume element is written as

$z\sim5\!-\!6$5

under a flat $z\sim5\!-\!6$6CDM cosmology with $z\sim5\!-\!6$7, $z\sim5\!-\!6$8, and $z\sim5\!-\!6$9, where

$z\sim10$0

For $z\sim10$1, the comoving volume between $z\sim10$2 and 10, and similarly between $z\sim10$3 and 20, is described as being of order a few $z\sim10$4. For transient forecasts, the expected number is modeled as

$z\sim10$5

where $z\sim10$6 is the comoving supernova-rate density and $z\sim10$7 encodes cadence, time dilation, and photometric depth (Wang et al., 2019).

Foreground control is treated as a technical requirement rather than an afterthought. Zodiacal light is identified as the dominant sky background in the $z\sim10$8 range; JWST’s cryogenic design minimizes thermal backgrounds, but unresolved faint galaxies contribute confusion noise. Galactic cirrus motivates low-dust field selection, especially in the northern CVZ. Instrumental systematics include persistence, scattered light, flat-fielding, and PSF modeling. A plausible implication is that the survey was framed not simply as a transient search, but as a map-making experiment in which the stability and reproducibility of the imaging data are as scientifically consequential as raw depth.

5. The ultradeep spectroscopic program at cosmic noon

The implemented JWST-SUSPENSE ultradeep spectroscopic program, GO-2110, addresses a different problem: the formation and quenching histories of massive quiescent galaxies at $z\sim10$9, the period when the quiescent population rapidly emerges and the Universe builds a large fraction of its stellar mass (Slob et al., 2024). It uses NIRSpec/MSA with the medium-resolution G140M grating and F100LP filter, giving wavelength coverage of $2\!-\!5\,\mu\mathrm{m}$0 at $2\!-\!5\,\mu\mathrm{m}$1. For the median redshift $2\!-\!5\,\mu\mathrm{m}$2, this corresponds to rest-frame $2\!-\!5\,\mu\mathrm{m}$3 Å, including Mg I 5178 Å, prominent Fe I features, and, at higher redshift, Ca II H+K and the 4000 Å break.

The observations consist of two identical visits on 2024 January 2 and 4, using MSATA target acquisition with six alignment stars and a 379 s confirmation image. For each of two MSA configurations per visit, the program obtained 10 integrations of 1473 s, with nodding after every two exposures. This yields 14,730 s per configuration per visit and a total on-source integration time of 16.4 hr across both visits and configurations (Slob et al., 2024).

The sample was built in a single optimized COSMOS pointing overlapping UltraVISTA, COSMOS, and COSMOS-DASH. Quiescent candidates were selected from UltraVISTA DR3 using UVJ colors following Muzzin et al. (2013b), with $2\!-\!5\,\mu\mathrm{m}$4 and $2\!-\!5\,\mu\mathrm{m}$5, plus one fainter filler retained because it achieved adequate signal-to-noise. The final sample contains 73 galaxies: 20 quiescent candidates at $2\!-\!5\,\mu\mathrm{m}$6 and 53 star-forming comparison galaxies at $2\!-\!5\,\mu\mathrm{m}$7 (Slob et al., 2024).

A central design choice was flexible MSA mask construction. Quiescent targets used slitlets of 3–7 microshutters, averaging 5, with “unconstrained” midbar centering to maximize multiplexing. This increased the quiescent sample from approximately 11 to 20, at the cost of some signal-to-noise and increased exposure to bar-shadow and failed-open-shutter effects. Thirty-four galaxies have full spectral coverage, 18 of them quiescent (Slob et al., 2024).

The data reduction uses a modified JWST Science Calibration Pipeline v1.12.5 with CRDS v1183, with tuned snowball parameters, 1/f removal via grizli, opposite-nod background subtraction, and MSAEXP-based combination and outlier masking. Because the quiescent targets are extended, pathloss corrections use the uniformly illuminated slit calibration files, and residual slit losses are removed by multiplicatively rescaling 1D spectra to UltraVISTA Y/J/H photometry. The program also models the effective line-spread function, finding resolution factors $2\!-\!5\,\mu\mathrm{m}$8 higher than JDox across wavelength, with $2\!-\!5\,\mu\mathrm{m}$9 assumed for 6 of the 20 quiescent galaxies lacking morphology measurements (Slob et al., 2024).

The achieved data quality is central to the program’s scientific identity. Median per-Å signal-to-noise is measured over rest-frame 4600–4800 Å, and most quiescent spectra achieve continuum $\lambda_{\rm obs}=(1+z)\lambda_{\rm rest}.$0, specifically 18 galaxies at that level. Nearly all quiescent spectra show deep H$\lambda_{\rm obs}=(1+z)\lambda_{\rm rest}.$1, H$\lambda_{\rm obs}=(1+z)\lambda_{\rm rest}.$2, and H$\lambda_{\rm obs}=(1+z)\lambda_{\rm rest}.$3 absorption; Mg I 5178 Å is detected in 16 targets; Fe I lines and the G band are present in the majority; and the twelve highest-$\lambda_{\rm obs}=(1+z)\lambda_{\rm rest}.$4 targets show Ca II H+K and a strong 4000 Å break. Seven quiescent targets show [O II] $\lambda_{\rm obs}=(1+z)\lambda_{\rm rest}.$5, and seven show [N II], [O III], and/or Balmer emission, with line ratios indicating non-star-forming ionization, likely AGN, shocks, or post-AGB excitation (Slob et al., 2024).

6. Stellar populations, abundances, and quenching histories

The survey’s first major results concern detailed stellar populations and non-parametric star-formation histories. Joint spectrophotometric fitting with Prospector, combined with FSPS, the MILES library, MIST isochrones, a Chabrier IMF, and two non-parametric SFH parameterizations, shows that all 20 quiescent candidates are indeed quenched and lie more than $\lambda_{\rm obs}=(1+z)\lambda_{\rm rest}.$6 below the Leja et al. (2022) star-forming main sequence at their redshifts (Slob et al., 2024). Their surviving stellar masses span $\lambda_{\rm obs}=(1+z)\lambda_{\rm rest}.$7, mass-weighted ages are $\lambda_{\rm obs}=(1+z)\lambda_{\rm rest}.$8 Gyr, and SFH durations are $\lambda_{\rm obs}=(1+z)\lambda_{\rm rest}.$9 Gyr. Four of the 20 were already quiescent by $1Slob et al., 2024).

The program defines mass-weighted age as

$1

SFH duration as

$1

and the fraction of stellar mass formed before redshift $1

$1

The typical SFH, illustrated as a Gaussian, has $1Slob et al., 2024).

Elemental-abundance analysis extends this picture by measuring C, Mg, Si, Ca, Ti, Cr, and Fe for 15 massive quiescent galaxies at $1code alf$1Beverage et al., 2024). Compared to $1dex in [C/H], $1

These abundance patterns are interpreted in terms of delayed enrichment. The paper states that core-collapse supernovae produce $1Beverage et al., 2024). On that basis, depressed [C/H] and [Fe/H] are taken to imply rapid formation and quenching before substantial AGB and SNIa enrichment, with abundance-based star-formation durations of $1

The paper also formalizes abundance notation,

$1

and uses

$1

to derive a stellar mass–metallicity relation. Fitting the available $1

$1

with a normalization lower by $1Beverage et al., 2024). This is one of the survey’s clearest internal controversies, and it is presented as a modeling issue rather than an observational contradiction.

7. Resolved gradients, stellar kinematics, and evolutionary interpretation

JWST-SUSPENSE has also produced the first spatially resolved stellar-population gradients from NIRSpec-MSA for distant quiescent galaxies. Full-spectrum modeling of 8 galaxies at $1Cheng et al., 15 Sep 2025). The analysis defines

$1

or equivalently

$1

for $1

The physical reading of these gradients is twofold. First, older cores and younger outskirts are interpreted as evidence for inside-out quenching. Second, Mg-deficient cores are taken to suggest rapid central gas expulsion, plausibly linked to AGN or supermassive-black-hole feedback, such that core star formation terminates early and enrichment is truncated. At the same time, the paper states that flat [Fe/H] together with positive [Mg/H] and [Mg/Fe] remains puzzling, implying that pure timescale arguments are insufficient and that outflows, IMF variations, or later stellar accretion may also be required (Cheng et al., 15 Sep 2025). This is a second major interpretive tension in the survey literature.

The survey’s kinematic branch extends the picture from stellar populations to angular momentum retention. Forward modeling of ultra-deep NIRSpec/MSA absorption-line spectra for 15 quiescent galaxies at $1LSF variations (Slob et al., 4 Jun 2025). The intrinsic model adopts a thin disk with arctangent rotation curve and constant dispersion,

$1

Key observables are

$1

and the spin parameter

$1

Of the 15 galaxies, 10 are aligned well enough to measure rotational support, and all 10 are fast rotators in the $1Slob et al., 4 Jun 2025). Combining SUSPENSE with LEGA-C and lensed $1

$1

The dynamical analysis further defines

$1

with $1Slob et al., 4 Jun 2025). The paper argues that widespread fast rotation means quenching did not destroy rotating disk structures, and that later inside-out growth plus mostly minor mergers can drive the transition toward lower-spin massive early-type descendants.

Taken together, the stellar-population, abundance, gradient, and kinematic results define a coherent but not fully closed evolutionary narrative. Massive quiescent galaxies at cosmic noon appear to have formed early, often rapidly, retained substantial ordered rotation after quenching, and then evolved through a combination of progenitor bias, late-time star formation in some systems, and minor-merger-driven structural growth (Slob et al., 2024). At the same time, several open issues remain explicit in the survey literature: abundance-derived and Prospector-derived star-formation timescales are discrepant; the combination of flat [Fe/H] with positive [Mg/H] and [Mg/Fe] gradients resists simple interpretation; and orientation, PSF/LSF systematics, and sample size still limit some kinematic and resolved-population inferences (Beverage et al., 2024). The legacy value of JWST-SUSPENSE therefore lies not only in the measurements already obtained, but also in establishing the technical and interpretive framework for larger, more physically constrained JWST studies of reionization-era sources and of quiescent-galaxy assembly at cosmic noon.