Ashby, Matthew LMcCallum, Emily2025-09-1820252025-05-222025McCallum, Emily. 2025. Beyond the Stars: Optimizing Residual Images and Source Counts in Deep-Field Spitzer IRAC Mosaics. Bachelors Thesis, Harvard University Engineering and Applied Sciences.31931982https://p2p8-sa-zuvru-a9vusux.re-cotta.com/handle/1/42719243This thesis presents refined approaches for the development of source count catalogs and residual images for deep-field Spitzer Infrared Array Camera (IRAC) mosaics. Two well-known scientific fields, the Euclid Deep Field North (EDF-N) and the Euclid Deep Field Fornax (EDF-F), are analyzed at 3.6 microns and 4.5 microns, resulting in a final set of four residual images and source counts. The residual images are developed through an iterative point spread function (PSF) fit-and-subtract routine that is validated on the basis of normalized completeness and photometric accuracy. The source counts are cataloged as an additional component of the iterative subtraction method and evaluated for precision and completeness through the use of SourceXtractor++ and published historical IRAC source counts. Three of the four sets of final residual images and source count catalogs are well-suited for scientific use, specifically as they relate to the study of the cosmic infrared background and its broader cosmological implications.application/pdfenIRACMosaicsResidualsSource CountsSpitzerApplied mathematicsAstronomyAstrophysicsThesis or Dissertation2025-09-180009-0009-4886-6907