WIggle Corrector Kit for NIRSpEc Data: WICKED

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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 “ WI ggle C orrector K it for NIRSp E c D ata” (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.

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