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Arxiv: Improved Empirical Backgrounds for JWST NIRISS Image/WFSS Data Reduction Published: 9/30/2024 9:00:02 PM Updated: 9/30/2024 9:00:02 PM

Paper abstract: The Near Infrared Imager and Slitless Spectrograph (NIRISS) on the James WebbSpace Telescope (JWST) is a versatile instrument for collecting imaging andwide-field slitless spectroscopy (WFSS) data for surveys of galaxy clusters,emission-line galaxies, stellar populations, and more. Dispersed zodiacal lightimprints distinct structures on space-based near-infrared imaging and WFSSobservations, necessitating careful subtraction during JWST NIRISS datareduction. As of 2024-09-24 NIRISS WFSS calibration backgrounds introducesignificant spatially-dependent artifacts, up to 5% of the overall backgroundlevel, which can severely affect data quality and following astronomicalanalysis. Notably, there are no existing backgrounds for NIRISS imaging datawhich also show systematic artifacts, such as the `light saber' effect. In thiswork, we present improved empirical JWST NIRISS imaging and WFSS backgroundsderived from all available public data in the F115W, F150W, and F200W filters.We demonstrate that our empirical backgrounds provide a more accuraterepresentation of the background structure in NIRISS imaging and WFSS data thanexisting reference files, mitigating the impact of spatially-dependentartifacts. Our empirical backgrounds are publicly available and can be used toimprove the quality of JWST NIRISS imaging and WFSS data reduction.