Using JWST to Investigate Dust Energy Balance in Galaxies at Cosmic Noon

The launch of the James Webb Space Telescope (JWST) has opened a new window onto the high-redshift Universe, enabling detailed studies of ionised gas and dust emission in distant galaxies. In this thesis, I perform mid-infrared photometry with the JWST Mid-Infrared Instrument (MIRI) for galaxies in the COSMOS field, focusing on the Blue Jay survey (1.7 < z < 3.5). The goal is to test the validity of the dust energy balance assumption used in spectral energy distribution (SED) fitting to infer the physical properties of galaxies. I developed a self-consistent photometric workflow that produces astrometrically aligned cutouts, RGB composite images, and aperture photometry across four MIRI filters (F770W, F1000W, F1800W, and F2100W), resulting in a comprehensive photometric catalogue. The analysis uses publicly available JWST imaging from the PRIMER, COSMOS-Web, and COSMOS-3D surveys. Background subtraction, artefact removal, and source masking were implemented to ensure robust measurements. The photometry was validated against the COSMOS2025 catalogue in F770W, confirming consistency of the results and adopted units. To test dust energy balance, I compare the measured MIRI fluxes with predictions from existing Prospector model fits based on HST, NIRCam, and NIRSpec data that exclude MIRI photometry. While the models broadly reproduce infrared fluxes, they systematically overestimate dust emission, particularly at longer wavelengths. The dependence on dust attenuation suggests that energy balance between absorbed and re-emitted light may not fully capture the complex underlying physics behind dust emission. This work establishes a reproducible framework for JWST/MIRI studies, demonstrating the opportunities and challenges of modelling panchromatic SEDs of galaxies at cosmic noon. It provides a critical evaluation of dust energy balance and its capability of extrapolating dust emission when infrared observations or strong priors are unavailable.