The MIRI/MRS Library. III. Detector-based optimal spectral extraction and high-contrast imaging applications

Abstract

(Abridged) JWST has now been operational for five years, and the associated data reduction pipelines have reached maturity. For MIRI/MRS, one can generally get a good-quality spectrum by simply running the standard pipeline, especially for unresolved sources. However, users are starting to look deeper into the data, trying to detect the smallest features in the faintest objects, and find close companions. Following the corrections derived in Papers I and II in this series, we now introduce a novel way to extract MIRI/MRS spectra: from the detectors directly. Currently the most common way to analyse data from integral field spectrometers is to reconstruct a spectral cube from the detector images. Theoretically, detector-extracted spectra could reach higher S/N, and better handle bad pixels. We generate stable and well-sampled PSF models using the sub-pixel scan of calibration star 10 Lac observed in PID 3779. These PSFs were used in a detector-based optimal extraction algorithm building on past approaches, where the contributions per pixel were weighted by their noise properties and contribution to the total illumination. The PSF models were used to subtract the PSF of a bright central source from the detector, both by direct subtraction, and a PCA approach. We find that our optimal setup allows us to get a $>$1.5 times higher S/N compared to the standard pipeline cube extraction. However, we approximately matched more involved cube processing. We were able to subtract the PSF to sub-percent levels, allowing us to extract spectra from faint companions. The novel approach greatly improves on the current standard pipeline reduction. We have not yet reached the fundamental noise limits. There are clear points of improvement that can be addressed using additional data. We demonstrate that detector-based processing of MIRI/MRS data has great potential.