A Five-Stage Framework for Slitless Grism Spectra: Demonstrated on Euclid Q1 Strong-Lens Candidates and Ported to CEERS NIRCam

TL;DR

This paper introduces a five-stage framework for extracting and analyzing slitless grism spectra in complex regimes, demonstrated on Euclid and CEERS data, improving redshift accuracy and portability across instruments.

Contribution

The paper presents a novel five-stage spectral extraction framework that enhances redshift determination in crowded slitless spectroscopy, applicable to multiple space telescopes.

Findings

473 Euclid Q1 lens candidates analyzed with high success rate

Median source redshift uncertainty reduced from 0.43 to 0.18

Portability of spectral analysis demonstrated on CEERS JWST/NIRCam data

Abstract

Wide-field slitless grism spectroscopy is difficult in the co-spatial regime, where multiple sources share one cross-dispersion PSF element and catalogue-level decontamination (aXe/LINEAR/Grizli) does not apply -- the regime of strong lenses, binary AGN, and mergers in HST, JWST, Euclid, and Roman grism data. This paper presents a five-stage framework for per-source 1-D spectra and redshifts: distortion-calibrated extraction, Fourier/Sersic/NNLS deblending, robust-PCA cleaning, weighted friend-of-friend with Hungarian cross-orientation matching, and a Bayesian posterior layer. Of 579 published Euclid Q1 lens candidates, 473 fall in the NISP footprint. A 3" DESI DR1 Iron match gives 57 counterparts (51 ZWARN=0, 46 clean v6d anchors). Extending to 9200 A adds features below 12500 A in 312 source and 324 deflector spectra. Source/deflector features are detected in 467/471 of 473; 371 source redshifts are secure, 75 probable, 21 tentative. Adopted z_def is filled for 440/473 (55 DESI + 385 PHZ MODE_1). Catalogue: 342 complete, 29 source-only, 75 Silver, 21 Bronze, 6 none. Posteriors succeed for 398/473; DESI deflector coverage is 0.67+/-0.07 (46 anchors). Tiers platinum/gold/silver/bronze/none = 62/230/82/24/75. Median source 68% CI is dz=1.30; DESI |dz|<0.1 recovery is 35%. Source-side support is synthetic-only; the full deblender's real-data performance is unmeasured here. A ported v6c on 10 CEERS DR0.7 JWST/NIRCam targets improves median |dz|/(1+z) from 0.43 to 0.18, recovers 4/10 within 0.10, and contains truth in the 68% CI for 8/10 -- portability across instruments, not independent calibration. The release is a 473-row catalogue with deflector redshifts, posterior intervals, and quality tiers.