Left Top:Herschel/SPIRE 250 μm map of the COSMOS field, used in the forward modeling framework of LinSimStack as the data vector d. This corresponds to our z ∼ 0.65 tomographic bin for [CII]-158 μm. Left Middle: Model m from LinSimStack, a linear combination of hit-maps of individual bins, convolved with the 250 μm beam, with the coverage mask of COSMOS2020 applied. Top Right: Residuals d − m not resolved by LinSimStack. We overplot the positions of the brightest 500 COSMOS sources in the Herschel SPIRE Point Source Catalog at 250 μm. Bottom Left: Per-pixel noise in the 250 μm map. Bottom middle: Histograms of the data, LinSimStack fit, and the unresolved residuals, all scaled by the per-pixel noise level after masking. Each is mean-subtracted independently. The residuals are more (standard) Gaussian than the map, with a high-end tail noting the missing sources in the COSMOS2020 catalog. Bottom right: Flux in the map versus in the residuals at the pixel location of sources in the Herschel/SPIRE point source catalog. Also plotted is a linear fit, with each pixel location weighted by the SNR; this encapsulates a measure of how much LinSimStack under-resolves the HSPSC sources.