| Abstract: Giant low surface brightness (GLSB) galaxies are massive, gas-rich disk systems with low star-formation efficiencies, low metallicities, diffuse stellar disks, and extended H I reservoirs, yet their formation and evolutionary pathways remain poorly understood. We compile a multi-wavelength dataset for 15 nearby GLSBs using GALEX, DECaLS, and WISE/Spitzer imaging to construct radial surface-brightness and colour profiles. Most GLSBs exhibit extended ultraviolet (XUV) emission beyond the optical radius, indicating low-level star formation in extremely low-density environments, while a smaller subset shows no detectable XUV component. We perform spatially resolved SED fitting to recover radial star-formation histories, stellar mass distributions, and dust attenuation. For XUV-GLSBs, the inner (R25) disk and extended XUV regions are modeled separately, enabling direct comparison with non-XUV systems. This study probes the nature of outer-disk star formation in GLSBs, addressing episodic versus continuous growth, inside-out disk evolution, and the role of interactions or low-metallicity gas accretion. In the era of LSST, Euclid, and JWST, this study provide key constraints on the formation and evolution of extreme low surface brightness galaxies. |
