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A 3D Drizzle Algorithm for JWST and Practical Application to the MIRI Medium Resolution Spectrometer Published: 6/8/2023 10:32:18 PM Updated: 6/8/2023 10:32:18 PM

Paper abstract: We describe an algorithm for application of the classic `drizzle' techniqueto produce 3d spectral cubes using data obtained from the slicer-type integralfield unit (IFU) spectrometers on board the James Webb Space Telescope. Thisalgorithm relies upon the computation of overlapping volume elements (composedof two spatial dimensions and one spectral dimension) between the 2d detectorpixels and the 3d data cube voxels, and is greatly simplified by treating thespatial and spectral overlaps separately at the cost of just 0.03% inspectrophotometric fidelity. We provide a matrix-based formalism for thecomputation of spectral radiance, variance, and covariance from arbitrarilydithered data and comment on the performance of this algorithm for theMid-Infrared Instrument's Medium Resolution IFU Spectrometer (MIRI MRS). Wederive a series of simplified scaling relations to account for covariancebetween cube spaxels in spectra extracted from such cubes, findingmultiplicative factors ranging from 1.5 to 3 depending on the wavelength rangeand kind of data cubes produced. Finally, we discuss how undersampling producesperiodic amplitude modulations in the extracted spectra in addition to thosenaturally produced by fringing within the instrument; reducing suchundersampling artifacts below 1% requires a 4-point dithering strategy andspectral extraction radii of 1.5 times the PSF FWHM or greater.