Reliable determination of the mid-infrared thermal continuum in JWST/MIRI spectra of NGC 1514

Develop a robust approach or obtain suitable observations to reliably fit and determine the mid-infrared thermal dust continuum in the JWST MIRI Medium Resolution Spectrometer spectra of NGC 1514’s rings and inner shell, overcoming baseline inflections introduced by cosmic ray events in both source and background exposures.

Background

The MIRI spectra of NGC 1514 are dominated by bright lines ([S IV] 10.511 μm, [Ne III] 15.555 μm, [O IV] 25.890 μm). The authors attempted to fit thermal continua but encountered baseline inflections due to the cosmic ray history of both source and background observations, preventing reliable continuum determination.

Because the continuum could not be fitted, quantitative dust SED modeling based directly on the spectra was not possible; instead, the authors relied on imaging color-color ratios to infer approximate dust color temperatures (~200 K from F770W/F1280W and ~110 K from F1280W/F2550W).

References

Fitting thermal continua to the spectra was rendered impossible due to the various inflection points caused by the cosmic ray history of both the source observations as well as the two background observations.

— JWST/MIRI Study of the Enigmatic Mid-Infrared Rings in the Planetary Nebula NGC 1514  (2502.21281 - Ressler et al., 28 Feb 2025) in Section 3.2 (Spectroscopy), caption of the figure showing spectra of all sampled locations

It is worth noting that the distinction between PAH emission and continuum varies between different spectral decomposition techniques and the nature of the mid-IR continuum itself is not fully settled in dust models.

— JWST Whirlpool Galaxy Treasury: Mid-Infrared Emission in M51 and its Relation to Gas Column and Star Formation  (2608.16802 - Padave et al., 17 Aug 2026) in Section 2, subsection “A note on the MIRI filters”