NEXUS: Quick Release Notes

arXiv:2603.04586 · astro-ph.IM, astro-ph.GA · Submitted 2026-03-04 · Read on arXiv

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Introduction to the show: ident: Astrophysics. The day in astrophysics: observations, models and what the data forces.

Vera: I'm Vera.

Jocelyn: And I'm Jocelyn, here with Subrahmanyan.

Vera: We're looking at the paper: "NEXUS: Quick Release Notes".

Jocelyn: Here's the gist of the paper. NEXUS describes JWST Multi-Cycle imaging and spectroscopic surveys around the North Ecliptic Pole to facilitate follow-up studies through regular Quick Data Releases.

Vera: The primary data covering the Deep tier (including NIRCam imaging, NIRSpec/MSA spectra, and vetted MSA spectroscopic redshifts) are released in regular Quick Data Releases to facilitate follow-up studies Survey Structure and Coverage NEXUS is a multi-cycle (Cycles 3-5) JWST imaging and spectroscopic survey around the North Ecliptic Pole, featuring two overlapping tiers The Wide tier covers a footprint of ∼ 400 arcmin2 and performs NIRCam imaging in six filters (F090W, F115W, F150W, F200W, F356W, and F444W) and WFSS slitless spectroscopy The Deep tier covers the central ∼ 50 arcmin2 within the Wide tier and performs NIRSpec MSA/PRISM spectroscopy and F200W+F444W NIRCam imaging on a 2-month cadence through early 2028 Target Selection Criteria Targets of different science categories are selected from the photometric catalog, classified into seven classes based on science category, each accompanied by a set of criteria on magnitude, photometric redshift (zphot), morphology, and colors Class 0 targets are transients and variables selected using difference imaging techniques in F200W and F444W filters observed at different epochs Class 1 targets are broad-line active galactic nuclei (AGNs) and little red dots (LRD) confirmed or candidates, targeted if they satisfy specific criteria related to optical or NIR spectra Class 2 objects are faint high-z galaxy candidates with specific magnitude and redshift criteria Class 3 targets are luminous quasar candidates satisfying quasar selection criteria and having a bright nucleus or barely resolved bulge Class 4 objects constitute the bulk of the sample with F444W<26 mag Class 5 targets are filler targets, being faint objects with F444W fainter than 27 mag but brighter than 27 mag in either F200W or F444W Data Processing and Quality Control The Quick-reduction MSA spectra are obtained by downloading stage 1 data products from MAST1 and reducing the NIRSpec MOS PRISM spectra using msaexp software paired with the JWST calibration pipeline For each Deep epoch, the following Quickrelease data products are released: 1.

Jocelyn: MSA target summary files containing MSAID, coordinates, source type, and priority class information 2.

Vera: NIRCam imaging mosaics and their corresponding uncertainty maps in F200W and F444W filters 3.

Paper summary: Vera: So we've heard that NEXUS is this multi-cycle survey around the North Ecliptic Pole, Cycles three through five. The core idea here is releasing quick data releases for the deep tier observations to guide prompt science analysis and follow-up observations >

Jocelyn: They are emphasizing how these quick data products serve that purpose directly, providing a way to get immediate insights from the deep epoch observations >

Subrahmanyan: What this means for cosmology is that getting those uniform spectroscopic redshifts for the sample with F444W less than or equal to twenty-six magnitudes will significantly boost the training sets we have for photometric redshift estimation > <ref:2603.04586#pg2>

Vera: That’s right. They are focusing on making sure we have a flux-complete galaxy sample that has solid redshifts, which is crucial when you're trying to use photometric redshifts to map out structure in the universe >

Jocelyn: And they are doing this through these regular cadence observations, which gives us a new way to look at high-redshift variability and characterize how things change over time >

Subrahmanyan: From a theoretical perspective, that variability information is key for studying black hole growth because we can look for changes in the continuum and emission lines during those events >

Vera: The survey structure itself is split into a wide tier covering about four hundred arcmin squared with NIRCam imaging and slitless spectroscopy, and the deep tier focusing on a central fifty arcmin squared area >

Jocelyn: And the target selection is really nuanced. They have seven classes of objects, from transients like Class zero to luminous quasar candidates like Class three > <ref:2603.04586#pg3>

Subrahmanyan: The classification system itself is interesting because it ties the selection criteria directly to specific astrophysical phenomena, like selecting little red dots or candidates for high-z galaxies >

Vera: And they have a few notable examples from their deep epochs. For instance, in Deep Epoch ten they observed eighteen Class zero objects and twenty-two Class one objects among the total counts > <ref:2603.04586#pg3>

Jocelyn: That kind of detailed cataloging helps us target specific science questions very quickly when we get those quick data releases >

Subrahmanyan: The deep epoch observations also show some interesting chance alignments, like in Deep Epoch three where they highlighted a galaxy at z = one point four three zero near a background object at z = four point eight eight six >

Vera: That kind of alignment is what we hope to find when we look at the full data sets because those are the kinds of connections that might tell us about structure formation across cosmic time >

Conclusion: Jocelyn: So, to wrap up, the NEXUS: Quick Release Notes paper is really about setting up this multi-cycle JWST survey around the North Ecliptic Pole and providing those quick data releases for the deep tier observations >

Vera: It’s about making sure that when we get these data products out, they are immediately useful for follow-up science, especially with getting robust spectroscopic redshifts for a large galaxy sample >

Subrahmanyan: The implication is that this regular cadence observation schedule allows us to substantially improve our ability to train photometric redshift estimation methods using high-quality spectroscopic anchors >

Jocelyn: And as a time-domain astronomer, it means we get a new window into high-redshift variability and characterization of both continuum and emission lines in objects like AGNs >

Vera: The authors are focusing heavily on the utility of this quick release structure to guide prompt science analysis and follow-up observations >

Subrahmanyan: Ultimately, this survey contributes to our understanding of galaxy evolution, black hole growth, and time-domain astrophysics through these deep tier observations >

Department of Astronomy, University of Illinois Urbana-Champaign · National Center for Supercomputing Applications, University of Illinois Urbana-Champaign · Department of Physics and Astronomy, University of Pennsylvania · Department of Astronomy & Astrophysics, UC San Diego · William H Miller III Department of Physics and Astronomy Johns Hopkins University · Space Telescope Science Institute · Department of Astrophysical Sciences Princeton University · Steward Observatory University of Arizona

astro-ph.IM, astro-ph.GA

Submitted: 2026-03-04

Updated: 2026-10-29

Comments: This is an arXiv-only document that describes the quick data releases from the NEXUS-JWST program through 2028. This document will be updated regularly to follow the cadenced observations from NEXUS (with a delay of ~2 months after each epoch). Data products are available at https://ariel.astro.illinois.edu/nexus/qdr/. Please send comments and suggestions to M. Zhuang and Y. Shen

License: http://creativecommons.org/licenses/by/4.0/

Importance score: 97/100

The gist: NEXUS describes JWST Multi-Cycle imaging and spectroscopic surveys around the North Ecliptic Pole to facilitate follow-up studies through regular Quick Data Releases.

Key concepts

Wide Tier: This tier covers a large area of about 400 arcmin2. It performs NIRCam imaging using six different filters (F090W to F444W) and uses WFSS slitless spectroscopy to survey a wide field of the sky.
Deep Tier: The Deep tier focuses on a central area of about 50 arcmin2 within the Wide tier. It performs detailed spectroscopy using NIRSpec MSA/PRISM and uses F200W+F444W NIRCam imaging on a two-month cycle through early 2028.
Class Targets: Targets are categorized into seven classes based on science category. These classes (e.g., Class 1 for AGNs, Class 3 for luminous quasars) are selected using criteria related to their magnitude, photometric redshift, morphology, and colors to guide specific scientific investigations.
Quick Data Releases: Data products are released regularly in Quick Data Releases. These releases include target summaries, NIRCam imaging mosaics with uncertainty maps, and reduced MSA spectra files. This regular cadence allows for rapid follow-up studies.

Terminology

Spectral Gap — 6× in this paper · explained in 6 episodes
Calibration — 3× in this paper · explained in 9 episodes
Little Red Dots — 3× in this paper · explained in 2 episodes
Adam — 1× in this paper · explained in 3 episodes
Core — 1× in this paper · explained in 2 episodes
Signal-to-Noise Ratio (SNR) — 1× in this paper · explained in 6 episodes

Summary

NEXUS describes JWST Multi-Cycle imaging and spectroscopic surveys around the North Ecliptic Pole to facilitate follow-up studies through regular Quick Data Releases. The primary data covering the Deep tier (including NIRCam imaging, NIRSpec/MSA spectra, and vetted MSA spectroscopic redshifts) are released in regular Quick Data Releases to facilitate follow-up studies

Survey Structure and Coverage

NEXUS is a multi-cycle (Cycles 3-5) JWST imaging and spectroscopic survey around the North Ecliptic Pole, featuring two overlapping tiers The Wide tier covers a footprint of ∼ 400 arcmin2 and performs NIRCam imaging in six filters (F090W, F115W, F150W, F200W, F356W, and F444W) and WFSS slitless spectroscopy The Deep tier covers the central ∼ 50 arcmin2 within the Wide tier and performs NIRSpec MSA/PRISM spectroscopy and F200W+F444W NIRCam imaging on a 2-month cadence through early 2028

Target Selection Criteria

Targets of different science categories are selected from the photometric catalog, classified into seven classes based on science category, each accompanied by a set of criteria on magnitude, photometric redshift (zphot), morphology, and colors Class 0 targets are transients and variables selected using difference imaging techniques in F200W and F444W filters observed at different epochs Class 1 targets are broad-line active galactic nuclei (AGNs) and little red dots (LRD) confirmed or candidates, targeted if they satisfy specific criteria related to optical or NIR spectra Class 2 objects are faint high-z galaxy candidates with specific magnitude and redshift criteria Class 3 targets are luminous quasar candidates satisfying quasar selection criteria and having a bright nucleus or barely resolved bulge Class 4 objects constitute the bulk of the sample with F444W<26 mag Class 5 targets are filler targets, being faint objects with F444W fainter than 27 mag but brighter than 27 mag in either F200W or F444W

Data Processing and Quality Control

The Quick-reduction MSA spectra are obtained by downloading stage 1 data products from MAST1 and reducing the NIRSpec MOS PRISM spectra using msaexp software paired with the JWST calibration pipeline For each Deep epoch, the following Quickrelease data products are released:

MSA target summary files containing MSAID, coordinates, source type, and priority class information
NIRCam imaging mosaics and their corresponding uncertainty maps in F200W and F444W filters
Quick-reduction MSA spectra files placed under “/nirspec/fits/”

Scientific Outcomes and Cadence

The uniform availability of spectroscopic redshifts for an unbiased, flux-complete galaxy sample (F444W≲26 mag) will substantially improve spectroscopic training sets for photometric redshift estimation The regular cadenced observations further open a new window for high-redshift variability studies, enabling the discovery of transients and the characterization of both continuum and emission-line variability in AGNs In each MSA epoch, approximately 550 objects have robust spectroscopic redshift after visual inspection The NEXUS Deep-tier data enable a broad range of scientific investigations spanning stellar and galaxy evolution, black hole growth, and time-domain astrophysics

Deep Epoch Observations

Deep Epoch 1 observed 758 objects in total, including 24 class=1 objects, 41 class=2 objects, 28 class=3 objects, and 665 class=4 objects Noteworthy sources highlighted include a z = 4.522 little-red-dot (LRD; MSAID=23192) and a z = 4.496 post-starburst (MSAID=27946) Deep Epoch 3 highlighted a chance alignment of a z = 1.430 galaxy (MSAID=5211) with a background object at z = 4.886, alongside a dual AGN candidate (MSAID=25745) Deep Epoch 5 highlighted the host galaxies of two transients at z = 1.946 (MSAID=36677) and z = 2.

Improvements for AI systems

Automated target selection for JWST follow-up can be improved by implementing a dynamic weighting scheme based on science category priority classes, as described in Section 2.1, to control their observing probability and priority. This allows the system to prioritize targets such as Class 0 transients or Class 3 luminous quasar candidates more effectively than a uniform selection process.
Enhanced transient detection and characterization systems can be developed by integrating new NIRCam imaging data with existing Deep epoch observations, specifically by stacking the EDR data with Deep Epoch 1 NIRCam mosaics to generate an updated MSAID catalog, which significantly increases tiling efficiency and target completeness.
Spectroscopic redshift estimation models for high-redshift galaxies can be refined by incorporating visual inspection feedback from M. Zhuang on the resulting spectra, as the paper notes that Initial spectroscopic redshifts are derived using the fit redshift function in msaexp, adopting the agn blue sfhz 13 template set from EAZY (Brammer et al. 2008), and are subsequently visually inspected by M. Zhuang.
Time-domain astrophysics AI systems can be improved by systematically studying transient number densities and their cosmic evolution through the properties of their host galaxies, leveraging the regular cadence of the NEXUS Deep Epoch observations for this systematic study.

Abstract

NEXUS is a JWST Multi-Cycle (Cycles 3-5) GO Treasury imaging and spectroscopic survey around the North Ecliptic Pole during 2024-2028. It contains two overlapping tiers in depth and area coverage. The Wide tier (about 400 arcmin squared) performs NIRCam/WFSS 2.4-5 μ m grism spectroscopy with three annual epochs over 3 years (final spectral continuum S/N/pixel>3 at F444W <22.2), accompanied by NIRCam multi-band imaging in F090W, F115W, F150W, F200W, F356W and F444W. The Deep tier (about 50 arcmin squared) performs high-multiplexing NIRSpec 0.54-5.5 μ m MOS/PRISM spectroscopy for 10,000 targets in total, over 18 epochs with a 2-month cadence, along with F200W+F444W NIRCam imaging for each epoch. Parallel imaging observations with MIRI and additional NIRCam filters are also performed within the Wide and Deep tiers. The primary data covering the Deep tier (including NIRCam imaging, NIRSpec/MSA spectra, and vetted MSA spectroscopic redshifts) are released in regular Quick Data Releases to facilitate follow-up studies. This evolving document describes the MSA targeting information and observing status for each of the 18 Deep epochs, which started in May 2025 and continue on the regular 2-month cadence. We also describe the content and caveats of the quick release data and report selected cases of diverse scientific interests.