Improved Empirical Backgrounds for JWST NIRISS Image/WFSS Data Reduction

TL;DR

This paper presents improved empirical background models for JWST NIRISS imaging and WFSS data, reducing artifacts and enhancing data quality for astronomical observations.

Contribution

The authors develop and provide new empirical background files for NIRISS imaging and WFSS, addressing systematic artifacts not covered by existing references.

Findings

Empirical backgrounds better match observed data structures.

Mitigation of spatially-dependent artifacts in NIRISS data.

Public availability of improved background models.

Abstract

The Near Infrared Imager and Slitless Spectrograph (NIRISS) on the James Webb Space Telescope (JWST) is a versatile instrument for collecting imaging and wide-field slitless spectroscopy (WFSS) data for surveys of galaxy clusters, emission-line galaxies, stellar populations, and more. Dispersed zodiacal light imprints distinct structures on space-based near-infrared imaging and WFSS observations, necessitating careful subtraction during JWST NIRISS data reduction. As of 2024-09-24 NIRISS WFSS calibration backgrounds introduce significant spatially-dependent artifacts, up to 5% of the overall background level, which can severely affect data quality and following astronomical analysis. Notably, there are no existing backgrounds for NIRISS imaging data which also show systematic artifacts, such as the `light saber' effect. In this work, we present improved empirical JWST NIRISS imaging and WFSS backgrounds derived from all available public data in the F115W, F150W, and F200W filters. We demonstrate that our empirical backgrounds provide a more accurate representation of the background structure in NIRISS imaging and WFSS data than existing reference files, mitigating the impact of spatially-dependent artifacts. Our empirical backgrounds are publicly available and can be used to improve the quality of JWST NIRISS imaging and WFSS data reduction.