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Accuracy of JWST MIRI/MRS Channel 4 flux extraction and background subtraction

Ascertain the accuracy and reliability of the JWST MIRI/MRS pipeline’s extraction of supernova flux and removal of instrumental and host-galaxy background in Channel 4 (approximately 17.7–28 µm), including quantifying systematic errors and developing validated methods for faint point sources embedded in complex backgrounds.

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Background

The authors developed a custom reduction pipeline tailored to faint point sources with complex backgrounds in MIRI/MRS data cubes. While flux calibration is thought to be accurate for Channels 1–3 and has been cross-validated with photometry, the behavior in Channel 4 is more uncertain due to increased instrumental background and challenges in background subtraction.

Given the importance of long-wavelength features for nebular-phase diagnostics, establishing robust extraction and calibration procedures for Channel 4 is necessary to interpret spectra (e.g., line strengths and ratios) and to compare results across epochs and instruments.

References

However, it is not yet known how well the pipeline extracts the SN flux in Channel 4, and how successful it is at accurately removing the background from both the instrument and the underlying host galaxy.

— A JWST Medium Resolution MIRI Spectrum and Models of the Type Ia supernova 2021aefx at +415 d (2404.17043 - Ashall et al., 25 Apr 2024) in Section 2 (Observations and Data Reduction)