WIggle Corrector Kit for NIRSpEc Data: WICKED

¹ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
² Department of Physics and Astronomy, University of Utah 115 South 1400 East, Salt Lake City, UT 84112, USA
³ European Space Agency, Space Telescope Science Institute, Baltimore, MD, USA
⁴ Department of Astronomy & Astrophysics and Institute for Gravitation and the Cosmos, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802, USA
⁵ Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08544, USA
⁶ Department of Astronomy, University of Michigan, 1085 S. University Avenue, Ann Arbor, MI 48109, USA
⁷ Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, China
⁸ Department of Astronomy, School of Physics, Peking University, Beijing 100871, China
⁹ George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy and Department of Physics and Astronomy, Texas A&M University, College Station, TX 77843, USA
¹⁰ European Space Research and Technology Centre, Keplerlaan 1, 2200 AG Noordwijk, The Netherlands

^★ Corresponding author: antoine.dumont.neira@gmail.com

Received: 12 March 2025
Accepted: 1 September 2025

Abstract

Context. The point spread function of the integral field unit (IFU) mode of the Near-Infrared Spectrograph (NIRSpec) detector of JWST is undersampled. The resampling of the spectra into a 3D data cube creates resampling noise seen as low-frequency sinusoidal-like artifacts, or “wiggles.” These artifacts in the data are not corrected in the JWST data pipeline and significantly impact the science that can be achieved at a single-pixel level.

Aims. Here we present the tool “WIggle Corrector Kit for NIRSpEc Data” (WICKED) designed to remove these artifacts. While fully characterizing wiggles requires forward modeling of the instrument response, WICKED offers a faster and computationally efficient alternative using an empirical correction.

Methods. WICKED uses the fast Fourier transform algorithm to identify wiggle-affected spaxels across the (IFU) data cube. Spectra are modeled with a mix of integrated aperture and annular templates, a power law, and a second-degree polynomial, thus avoiding the high-degree polynomials that distort spectral features. Our correction works across all medium- and high-resolution NIRSpec gratings: F070LP, F100LP, F170LP, and F290LP.

Results. The overall spectral shape recovered by WICKED is up to 3.5 times better compared to uncorrected spectra. It recovers the equivalent width of absorption lines within 5% of the true value, which is also roughly three times better than the uncorrected spectra. WICKED7 significantly improves kinematic measurements, recovering the line-of-sight velocity (LOSV) within 1% of the true value – more than 100 times better than uncorrected spectra at S/N ~ 40. As a case study, we applied WICKED to G235H/F170LP IFU data of the elliptical galaxy NGC 5128, finding good agreement with previous studies. In wiggle-affected regions, the uncorrected spectrum showed a stellar LOSV and velocity dispersion differences ~17 times and ~36 times larger than the estimated uncertainties, respectively, compared to the WICKED-cleaned spectrum.

Conclusions. Wiggles in NIRSpec IFU data can significantly distort the overall spectral shape and bias line measurements and kinematics to values larger than the expected uncertainties for uncorrected spectra. WICKED is a robust, user-friendly solution for mitigating wiggles in NIRSpec data that enables precise single-spaxel studies and enhances JWST’s potential for groundbreaking discoveries in galaxy kinematics and early Universe studies.