CONGRESS NIRCam Grism Survey Overview

• The survey is a complete NIRCam grism redshift program using JWST Cycle 2 F356W imaging to extend Hα coverage over 3.8<z<5.1.
• It employs advanced forward-modeling and blind-search techniques for robust redshift assignment and high-resolution (R~1500) emission-line measurements.
• The dataset integrates CONGRESS with FRESCO and JADES to enable detailed studies of luminosity functions, protoclusters, ionized-gas kinematics, and AGN demographics.

The CONGRESS NIRCam Grism Survey is the Complete NIRCam Grism Redshift Survey, a JWST Cycle 2 wide-field slitless spectroscopic program in GOODS-North that uses NIRCam WFSS with the F356W grism configuration over 62 arcmin$^2$. In the published literature, CONGRESS is most often analyzed jointly with FRESCO and JADES, forming a coordinated GOODS-field dataset for rest-optical emission-line spectroscopy, morphology, photometry, and redshift confirmation at high redshift. Its primary scientific role has been to extend H$\alpha$ coverage to approximately $3.8 in GOODS-N, while the combined CONGRESS+FRESCO setup provides continuous $3.1$–$5.0\,\mu\mathrm{m}$ grism coverage and underpins studies of luminosity functions, protoclusters, ionized-gas kinematics, and faint broad-line AGNs at $z\gtrsim4$ (Covelo-Paz et al., 2024, Danhaive et al., 27 Mar 2025, Zhang et al., 5 May 2025).

1. Survey identity and observational scope

CONGRESS is identified in the literature as the Cycle 2 JWST Complete NIRCam Grism Redshift Survey in GOODS-N, with proposal ID 3577. Its observational core is NIRCam slitless grism spectroscopy with the F356W filter over 62 arcmin$^2$. In this configuration, the survey probes H$\alpha$ over approximately $3.8, because the rest wavelength of H$\alpha$ falls inside the F356W grism bandpass. In most science analyses, CONGRESS is paired with the Cycle 1 FRESCO survey, which supplies F444W grism spectroscopy in GOODS-N and GOODS-S and extends H$\alpha$0 coverage to $\alpha$1 (Covelo-Paz et al., 2024, Zhang et al., 5 May 2025, Lin et al., 5 May 2025).

Program element	Configuration in the literature	Role in CONGRESS-based analyses
CONGRESS	GOODS-N; F356W grism; 62 arcmin$\alpha$2	H$\alpha$3 at $\alpha$4
FRESCO	GOODS-N/S; F444W grism; 62 arcmin$\alpha$5 per field	H$\alpha$6 at $\alpha$7
JADES	Deep JWST imaging in GOODS fields	Morphology, photometry, structural priors

This joint architecture is scientifically consequential because it converts CONGRESS from a single-filter survey into the lower-wavelength half of a broader GOODS-N rest-optical spectroscopic baseline. In practice, the literature uses CONGRESS not as an isolated dataset but as a key component of a larger JWST observational stack that couples slitless spectroscopy to deep imaging and SED constraints (Covelo-Paz et al., 2024, Danhaive et al., 27 Mar 2025).

2. Instrumental basis in JWST/NIRCam slitless spectroscopy

The survey depends on the long-wavelength slitless spectroscopy capability of JWST/NIRCam. NIRCam has two nearly identical modules, A and B, each with a $\alpha$8 field of view, and each long-wavelength channel contains two identical Si grisms with perpendicular orientations. These grisms provide slitless spectroscopy over $\alpha$9 at approximately $3.8, enabling simultaneous spectroscopy of essentially all objects in the field while retaining the multiplex advantage of imaging-based surveys (Greene et al., 2016).

The underlying optics are monolithic silicon grisms designed for nearly undeviated transmission, high resolving power, and compatibility with pupil-wheel architectures. The NIRCam grisms were built for the $3.8 range, and their as-built performance met demanding astronomical requirements for surface figure, groove roughness, scattering, and ghost suppression. This instrumental maturity is directly relevant to CONGRESS because it underwrites moderate-resolution slitless spectroscopy in the wavelength range where H$3.8Deen et al., 2016).

The slitless mode also imposes the central technical constraint of the survey: spectra overlap, and morphology is convolved with dispersion. That tradeoff is structural rather than incidental. It explains both the efficiency of CONGRESS for large samples and the later development of dedicated forward-modelling pipelines for contamination control, redshift assignment, and kinematic inference (Greene et al., 2016, Danhaive et al., 8 Oct 2025).

3. Catalog construction and redshift-assignment methodology

Published CONGRESS analyses use two closely related catalog-building strategies. One is a blind-search framework in NIRCam/grism data that begins with photometric and spectroscopic redshift priors, extracts grism spectra with grizli, searches for emission lines, requires initial H$3.8, and then applies visual inspection with a final quality cut of $3.8. In that implementation, the final catalog contains 1,050 H$3.8, of which 554 are identified from CONGRESS in GOODS-N (Covelo-Paz et al., 2024).

A second strategy uses a semi-automated redshift assignment algorithm. It first identifies robust emission lines in 1D and 2D spectra, then performs a coarse cross-correlation over $3.1$0 in steps of $3.1$1, followed by a refined search on a grid of $3.1$2 around candidate peaks. The refined fit uses empirical line-ratio templates for common complexes such as

$3.1$3

and

$3.1$4

Applied to GOODS-N CONGRESS+FRESCO data, this pipeline yielded a final science sample of 888 H$3.1$5-emitting galaxies at $3.1$6 over an effective area of about 62 arcmin$3.1$7, reaching $3.1$8 (Lin et al., 10 Apr 2025).

Completeness modeling is correspondingly formalized. In the blind-search luminosity-function analysis, the total completeness is decomposed into photometric detection completeness, grism extraction completeness, line-detection completeness, and visual-inspection completeness, and luminosity bins with average completeness below 65% are excluded. This methodology is central to the survey’s statistical use, because CONGRESS-based results depend on a tractable spectroscopic selection function rather than on purely photometric reconstruction (Covelo-Paz et al., 2024).

4. H$3.1$9 emitters, luminosity functions, and large-scale structure

CONGRESS has been a primary source of the first large, spectroscopically confirmed H$5.0\,\mu\mathrm{m}$0 samples beyond $5.0\,\mu\mathrm{m}$1. In the GOODS fields, the combined CONGRESS+FRESCO catalog enabled the first purely spectroscopic H$5.0\,\mu\mathrm{m}$2 luminosity functions at $5.0\,\mu\mathrm{m}$3, with redshift bins centered at $5.0\,\mu\mathrm{m}$4, $5.0\,\mu\mathrm{m}$5, and $5.0\,\mu\mathrm{m}$6. The corresponding cosmic star-formation-rate densities, integrated to a common limit in that analysis, are $5.0\,\mu\mathrm{m}$7–$5.0\,\mu\mathrm{m}$8, $5.0\,\mu\mathrm{m}$9, and $z\gtrsim4$0, implying a decline by a factor of about 3 from $z\gtrsim4$1 to $z\gtrsim4$2 (Covelo-Paz et al., 2024).

In GOODS-N alone, CONGRESS-based studies identified major overdense structures. One analysis reported 98 H$z\gtrsim4$3 emitters at $z\gtrsim4$4 in the CONGRESS footprint (Covelo-Paz et al., 2024). A clustering-focused analysis then resolved two prominent filamentary protoclusters at $z\gtrsim4$5 and $z\gtrsim4$6, hosting 98 and 144 HAEs, respectively. Their geometry matters: the $z\gtrsim4$7 system spans about 10 cMpc across the sky and 25 cMpc along the line of sight, while the $z\gtrsim4$8 system extends about 15 cMpc transversely and 70 cMpc along the line of sight (Lin et al., 10 Apr 2025).

The environmental consequences are substantial. In the same work, the observed H$z\gtrsim4$9-based star-formation-rate density is $^2$0 and $^2$1 at $^2$2–5 and $^2$3–6, with protoclusters contributing approximately 25% and 55%, respectively. The field HAE auto-correlation yields correlation lengths of $^2$4 at $^2$5–5 and $^2$6 at $^2$7–6, implying typical host halo masses of $^2$8 with a scatter of about 0.4 dex from comparison to UniverseMachine (Lin et al., 10 Apr 2025).

A recurrent conclusion is that CONGRESS-based H$^2$9 samples are not merely redshift catalogs. They provide a spectroscopic environmental tracer field dense enough to support three-dimensional structure studies at $\alpha$0, including luminosity-function splits by environment and SFR-limited clustering analyses (Covelo-Paz et al., 2024, Lin et al., 10 Apr 2025).

5. Ionized-gas morphology and kinematics

CONGRESS is also central to the first statistical studies of spatially resolved ionized-gas kinematics at very high redshift. A joint CONGRESS+FRESCO+JADES analysis modeled 272 H$\alpha$1 emitters at $\alpha$2, spanning $\alpha$3 and $\alpha$4, with the sample described as representative down to $\alpha$5. After selection, the sample comprised 41 gold, 132 silver, and 99 unresolved systems (Danhaive et al., 27 Mar 2025).

These studies rely on $\alpha$6, a forward-modelling Bayesian inference tool for NIRCam slitless spectroscopy. The code combines Sérsic emission-line morphology, arctangent rotation curves, full PSF and LSF convolution, and gradient-based sampling via $\alpha$7. It was explicitly framed as the methodological foundation for extracting intrinsic kinematics from CONGRESS-style WFSS data and for scaling such analyses to samples of order $\alpha$8 H$\alpha$9 emitters (Danhaive et al., 8 Oct 2025).

The main kinematic result is that the high-redshift H$3.8$3.8 and $3.8 at $3.8, with only a modest increase in the fraction of rotationally supported systems from $3.8 at $3.8 to $3.8 at $3.8 for galaxies with $3.8. This supports the view that disks exist at $3.8Danhaive et al., 27 Mar 2025).

CONGRESS also underpins size-kinematics studies of H$\alpha$0 emission. In a sample of 213 galaxies at $\alpha$1 from FRESCO and CONGRESS, the average H$\alpha$2 size at $\alpha$3 is $\alpha$4 at $\alpha$5, compared with continuum sizes of about $\alpha$6. The adopted size-mass-redshift parameterization is

$\alpha$7

The study further found that $\alpha$8 increases with distance above the star-forming main sequence, and that for galaxies with rising star-formation histories there is a positive correlation between $\alpha$9 and rotational support, with $\alpha$00 and $\alpha$01. A related morphological result is that about 44% of systems with $\alpha$02 are not rotationally supported, indicating that projected elongation is not a reliable proxy for disk kinematics at these epochs (Danhaive et al., 7 Oct 2025).

6. Broad-line AGNs, host galaxies, and environmental interpretation

CONGRESS has also become a major survey resource for faint high-redshift AGN studies. Using CONGRESS+FRESCO slitless spectroscopy in GOODS-N, one spectroscopic search identified 19 broad H$\alpha$03 emitters at $\alpha$04, including 10 from CONGRESS, 9 from FRESCO, and 9 newly identified sources. The selection required broad H$\alpha$05 FWHM $\alpha$06 and broad-component S/N $\alpha$07. The broad components have mean FWHM $\alpha$08, a range of 1077–3550 km/s, and mean broad-H$\alpha$09 luminosity $\alpha$10; the inferred black hole masses and bolometric luminosities indicate that most sources are accreting at about 10% of the Eddington limit (Zhang et al., 5 May 2025).

This AGN sample directly informed debates around Little Red Dots. In the same work, 42% of the broad H$\alpha$11 emitters do not satisfy widely used LRD color criteria, and 68% of color-selected LRDs with H$\alpha$12 detections in NIRCam/grism spectra do not show broad-line features. The paper interprets some steep red slopes as likely produced by line-boosting effects, especially from strong emission lines in broad filters, rather than by a unique broad-line AGN population (Zhang et al., 5 May 2025).

A separate CONGRESS-based environment study assembled 28 low-luminosity AGNs at $\alpha$13 and compared them with 782 H$\alpha$14 emitters selected from the same data. Measured on $\alpha$15 scales, the AGN overdensity field spans $\alpha$16 to 10.56 and shows no clear correlation with broad-line luminosity, black hole mass, or AGN fraction. The field AGN–HAE cross-correlation lengths are $\alpha$17 at $\alpha$18 and $\alpha$19 at $\alpha$20, implying host halo masses of $\alpha$21 and host stellar masses of $\alpha$22. The study concludes that these low-luminosity AGNs occupy ordinary star-forming environments rather than quasar-like extreme halos (Lin et al., 5 May 2025).

Host-galaxy decomposition sharpened that picture. In 17 AGN-host systems identified from CONGRESS and FRESCO broad H$\alpha$23 detections and analyzed with JADES imaging, extended emission was detected in 9/17 sources. For host-detected systems, stellar masses inferred after image decomposition can be 1–2 dex lower than values obtained without decomposition, and the inferred mass ratios span $\alpha$24. This has been interpreted in two ways: the hosts may be genuinely undermassive relative to their black holes, or a substantial fraction of host light may remain hidden in unresolved central components (Ma et al., 22 Jan 2026).

7. Position within JWST grism-survey astronomy

CONGRESS belongs to the maturation of JWST/NIRCam WFSS from technical capability to survey infrastructure. CEERS had already demonstrated, tested, and validated efficient extragalactic surveys using coordinated JWST observations that included NIRCam slitless grism spectroscopy, providing a direct observational precedent for later wide-field extragalactic grism programs (Finkelstein et al., 7 Jan 2025). Within that broader ecosystem, CONGRESS occupies the GOODS-N blank-field, F356W, rest-optical redshift-survey niche.

Related programs have emphasized different observing regimes: ALT used a deep F356W grism survey in the strong-lensing field Abell 2744 and introduced the “butterfly” mosaic for contamination control (Naidu et al., 2024); MAGNIF used medium-band NIRCam grism spectroscopy in Frontier Fields clusters to push H$\alpha$25 luminosity functions to lower intrinsic luminosities (Fu et al., 5 Mar 2025); SAPPHIRES used pure-parallel WFSS to search for extremely metal-poor galaxies at $\alpha$26 (Hsiao et al., 6 May 2025). Against that backdrop, CONGRESS is distinguished by its function as a complete GOODS-N spectroscopic census optimized for homogeneous high-redshift line-emitter samples and for direct comparison between star-forming galaxies and AGNs.

A plausible implication is that CONGRESS marks the point at which NIRCam slitless spectroscopy became a population-statistics instrument rather than only a discovery tool. The published CONGRESS-based literature now spans redshift catalogs, H$\alpha$27 luminosity functions, cosmic star-formation-rate density, protocluster geometry, galaxy kinematics, H$\alpha$28 size–mass relations, broad-line AGN demographics, host-galaxy decomposition, and AGN clustering. In that sense, the survey’s importance lies not in a single flagship result but in establishing a spectroscopic reference dataset for GOODS-N at the epoch when rest-optical tracers first become observable with JWST at scale (Covelo-Paz et al., 2024, Lin et al., 10 Apr 2025, Danhaive et al., 27 Mar 2025).