---
title: CONGRESS NIRCam Grism Survey Overview
url: https://www.emergentmind.com/topics/congress-nircam-grism-survey
type: topic
---

# CONGRESS NIRCam Grism Survey Overview

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 **\(3.8<z<5.1\)** 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 \(z\gtrsim4\) [2409.17241, 2503.21863, 2505.02895].

## 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 **\(3.8<z<5.1\)**, 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\(\alpha\) coverage to **\(4.9<z<6.7\)** [2409.17241, 2505.02895, 2505.02896].

| Program element | Configuration in the literature | Role in CONGRESS-based analyses |
|---|---|---|
| CONGRESS | GOODS-N; F356W grism; 62 arcmin\(^2\) | H\(\alpha\) at \(3.8<z<5.1\) |
| FRESCO | GOODS-N/S; F444W grism; 62 arcmin\(^2\) per field | H\(\alpha\) at \(4.9<z<6.7\) |
| 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 [2409.17241, 2503.21863].

## 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 **\(2.2\times2.2\)** field of view, and each long-wavelength channel contains **two identical Si grisms with perpendicular orientations**. These grisms provide slitless spectroscopy over **\(\lambda=2.4-5.0\,\mu\mathrm{m}\)** at approximately **\(R\sim1500\)**, enabling simultaneous spectroscopy of essentially all objects in the field while retaining the multiplex advantage of imaging-based surveys [1606.04161].

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 **\(2\)–\(5\,\mu\mathrm{m}\)** 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\(\alpha\), [\(\ion{O}{3}\)], and related rest-optical lines enter the observer-frame near-IR at \(z>3\) [1611.09923].

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 [1606.04161, 2510.07369].

## 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\(\alpha\) S/N \(>3\)**, and then applies visual inspection with a final quality cut of **\(q\ge1.75\)**. In that implementation, the final catalog contains **1,050 H\(\alpha\) emitters**, of which **554** are identified from CONGRESS in GOODS-N [2409.17241].

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 **\(z=0.1-10\)** in steps of **\(\delta z=0.1\)**, followed by a refined search on a grid of **\(\delta z=0.001\)** around candidate peaks. The refined fit uses empirical line-ratio templates for common complexes such as
\[
\mathrm{H}\beta + [\ion{O}{3}]\,\lambda\lambda4960,5008
\]
and
\[
\mathrm{H}\alpha + [\ion{N}{2}]\,\lambda\lambda6549,6585 + [\ion{S}{2}]\,\lambda\lambda6718,6732.
\]
Applied to GOODS-N CONGRESS+FRESCO data, this pipeline yielded a final science sample of **888 H\(\alpha\)-emitting galaxies** at **\(3.75<z<6\)** over an effective area of about **62 arcmin\(^2\)**, reaching **\(L_{\rm H\alpha}\sim10^{41.2}\ {\rm erg\ s^{-1}}\)** [2504.08028].

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 [2409.17241].

## 4. H\(\alpha\) emitters, luminosity functions, and large-scale structure

CONGRESS has been a primary source of the first large, spectroscopically confirmed H\(\alpha\) samples beyond \(z=3\). In the GOODS fields, the combined CONGRESS+FRESCO catalog enabled the first **purely spectroscopic H\(\alpha\) luminosity functions at \(z>3\)**, with redshift bins centered at **\(z\sim4.45\)**, **\(5.30\)**, and **\(6.15\)**. The corresponding cosmic star-formation-rate densities, integrated to a common limit in that analysis, are **\(0.041\)–\(0.042\)**, **\(0.029\)**, and **\(0.012\,M_\odot\,\mathrm{yr}^{-1}\,\mathrm{Mpc}^{-3}\)**, implying a decline by a factor of about **3** from \(z\sim4\) to \(z\sim6\) [2409.17241].

In GOODS-N alone, CONGRESS-based studies identified major overdense structures. One analysis reported **98 H\(\alpha\) emitters at \(z=4.43\pm0.03\)** in the CONGRESS footprint [2409.17241]. A clustering-focused analysis then resolved two prominent **filamentary protoclusters** at **\(z\approx4.41\)** and **\(z\approx5.19\)**, hosting **98** and **144** HAEs, respectively. Their geometry matters: the \(z\approx4.41\) system spans about **10 cMpc** across the sky and **25 cMpc** along the line of sight, while the \(z\approx5.19\) system extends about **15 cMpc** transversely and **70 cMpc** along the line of sight [2504.08028].

The environmental consequences are substantial. In the same work, the observed H\(\alpha\)-based star-formation-rate density is **\(0.050^{+0.002}_{-0.003}\)** and **\(0.046^{+0.006}_{-0.004}\,M_\odot\,{\rm yr}^{-1}\,{\rm Mpc}^{-3}\)** at **\(z=3.75\)–5** and **\(z=5\)–6**, with protoclusters contributing approximately **25%** and **55%**, respectively. The field HAE auto-correlation yields correlation lengths of **\(r_0=4.61^{+1.00}_{-0.68}\,h^{-1}{\rm Mpc}\)** at \(z\approx4\)–5 and **\(r_0=6.23^{+1.68}_{-1.13}\,h^{-1}{\rm Mpc}\)** at \(z=5\)–6, implying typical host halo masses of **\(\log(M_h/M_\odot)\approx11.0-11.2\)** with a scatter of about **0.4 dex** from comparison to **UniverseMachine** [2504.08028].

A recurrent conclusion is that CONGRESS-based H\(\alpha\) samples are not merely redshift catalogs. They provide a spectroscopic environmental tracer field dense enough to support three-dimensional structure studies at \(z>4\), including luminosity-function splits by environment and SFR-limited clustering analyses [2409.17241, 2504.08028].

## 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\(\alpha\) emitters** at **\(z\approx3.9-6.5\)**, spanning **\(\log(M_\star/M_\odot)\approx8-10\)** and **\(\mathrm{SFR}\approx0.3-100\,M_\odot\,\mathrm{yr}^{-1}\)**, with the sample described as representative down to **\(\log(M_\star/M_\odot)\approx9\)**. After selection, the sample comprised **41 gold**, **132 silver**, and **99 unresolved** systems [2503.21863].

These studies rely on **\(\texttt{geko}\)**, 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 **\(\texttt{jax}/\texttt{numpyro}\)**. 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 **\(\sim200\)** H\(\alpha\) emitters [2510.07369].

The main kinematic result is that the high-redshift H\(\alpha\) population is dynamically hot. The inferred typical values are **\(\sigma_0\approx100\ {\rm km\,s^{-1}}\)** and **\(v/\sigma_0\approx1-2\)** at **\(z\approx3.9-6.5\)**, with only a modest increase in the fraction of rotationally supported systems from **\((36\pm6)\%\)** at **\(z\sim5.5\)** to **\((41\pm6)\%\)** at **\(z\sim4.5\)** for galaxies with **\(9<\log(M_\star/M_\odot)<10\)**. This supports the view that disks exist at \(z\gtrsim4\) but do not dominate the population probed by the survey [2503.21863].

CONGRESS also underpins size-kinematics studies of H\(\alpha\) emission. In a sample of **213 galaxies at \(z\approx4-6\)** from **FRESCO and CONGRESS**, the average **H\(\alpha\)** size at **\(z\approx5\)** is **\(r_{\rm e,H\alpha}=1.17\pm0.05\ {\rm kpc}\)** at **\(\log(M_\star/M_\odot)=9.5\)**, compared with continuum sizes of about **\(0.9\ {\rm kpc}\)**. The adopted size-mass-redshift parameterization is
\[
\log \left(\frac{r_e}{\mathrm{kpc}}\right)
=
\alpha \log \left(\frac{M_\star}{10^{9.5}\,M_\odot}\right)
+
\beta
+
\gamma \log \left(\frac{1+z}{6}\right).
\]
The study further found that \(r_{\rm e,H\alpha}/r_{\rm e,NUV}\) increases with distance above the star-forming main sequence, and that for galaxies with rising star-formation histories there is a positive correlation between \(r_{\rm e,H\alpha}/r_{\rm e,NUV}\) and rotational support, with **\(\rho=0.31\)** and **\(p<0.001\)**. A related morphological result is that about **44%** of systems with **\(b/a<0.5\)** are **not rotationally supported**, indicating that projected elongation is not a reliable proxy for disk kinematics at these epochs [2510.06315].

## 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\(\alpha\) emitters** at **\(z\sim4-5.5\)**, including **10 from CONGRESS**, **9 from FRESCO**, and **9 newly identified** sources. The selection required **broad H\(\alpha\) FWHM \(>1000\ {\rm km\,s^{-1}}\)** and **broad-component S/N \(>3\)**. The broad components have mean **FWHM \(\approx2050\ {\rm km\,s^{-1}}\)**, a range of **1077–3550 km/s**, and mean broad-H\(\alpha\) luminosity **\(4.52\times10^{42}\ {\rm erg\,s^{-1}}\)**; the inferred black hole masses and bolometric luminosities indicate that most sources are accreting at about **10% of the Eddington limit** [2505.02895].

This AGN sample directly informed debates around **Little Red Dots**. In the same work, **42%** of the broad H\(\alpha\) emitters do **not** satisfy widely used LRD color criteria, and **68%** of color-selected LRDs with H\(\alpha\) 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 [2505.02895].

A separate CONGRESS-based environment study assembled **28 low-luminosity AGNs** at **\(3.9<z<6\)** and compared them with **782 H\(\alpha\) emitters** selected from the same data. Measured on \((15\,h^{-1}{\rm cMpc})^3\) scales, the AGN overdensity field spans **\(-0.56\)** 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 **\(r_0=4.26^{+0.70}_{-0.61}\,h^{-1}{\rm cMpc}\)** at **\(3.9<z<5\)** and **\(r_0=7.66^{+0.90}_{-0.81}\,h^{-1}{\rm cMpc}\)** at **\(5<z<6\)**, implying host halo masses of **\(\log(M_h/M_\odot)\approx11.0-11.2\)** and host stellar masses of **\(\log(M_\star/M_\odot)\approx8.4-8.6\)**. The study concludes that these low-luminosity AGNs occupy ordinary star-forming environments rather than quasar-like extreme halos [2505.02896].

Host-galaxy decomposition sharpened that picture. In **17** AGN-host systems identified from CONGRESS and FRESCO broad H\(\alpha\) 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 **\(M_{\rm BH}/M_\ast\sim0.01-1.48\)**. 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 [2601.15962].

## 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 [2501.04085]. 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 [2410.01874]; **MAGNIF** used **medium-band** NIRCam grism spectroscopy in Frontier Fields clusters to push H\(\alpha\) luminosity functions to lower intrinsic luminosities [2503.03829]; **SAPPHIRES** used **pure-parallel WFSS** to search for extremely metal-poor galaxies at \(z\sim5-7\) [2505.03873]. 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\(\alpha\) luminosity functions, cosmic star-formation-rate density, protocluster geometry, galaxy kinematics, H\(\alpha\) 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 [2409.17241, 2504.08028, 2503.21863].

Source: https://www.emergentmind.com/topics/congress-nircam-grism-survey