Source of the F1000W–MIRI LRS absolute calibration offset

Determine whether the observed approximately 0.04 mag systematic offset between synthetic JWST MIRI F1000W photometry derived from MIRI Low Resolution Spectrometer (LRS) spectra and the measured F1000W photometry is caused by the MIRI LRS spectroscopic absolute flux calibration (e.g., pathloss correction and slit-position effects) or by the MIRI F1000W photometric calibration, in order to establish which calibration requires revision.

Background

The authors compare synthetic F1000W photometry generated from MIRI LRS spectra to observed JWST MIRI F1000W photometry and find a systematic offset of approximately 0.04 magnitudes, with the synthetic photometry being fainter. This level is just over their adopted 3% photometric uncertainty.

Because F1000W is the only MIRI broadband filter whose entire bandpass lies within the MIRI LRS spectral range, the authors cannot isolate whether the discrepancy originates from the spectroscopic or photometric side. They note that the current JWST spectral pipeline does not include a true pathloss correction based on the actual slit point, which could plausibly contribute, but the definitive source of the offset remains unresolved.

References

Unfortunately, F1000W is the only observed photometry whose entire bandpass fits within the MIRI LRS spectral range, so we cannot determine whether this is an issue with the photometric or spectroscopic absolute flux calibration.

— Precise Bolometric Luminosities and Effective Temperatures of 23 late-T and Y dwarfs Obtained with JWST (2407.08518 - Beiler et al., 11 Jul 2024) in Section 4.2.2 (Pipeline Calibration — MIRI LRS)