Dr. Ronaldo Laishram

Galaxies grow, transform, and eventually quench across billions of years of cosmic history, but how internal structure, star formation, and large-scale environment are connected across different cosmic epochs remains an open question. In this talk, I present a coherent observational picture of galaxy structural evolution from z ~ 0.4 to the epoch of reionization, combining Subaru HSC narrowband imaging, JWST NIRCam, and HST. At z ~ 0.4, environmental analysis of Ha emitters around galaxy clusters provides direct evidence that environmental quenching was already operating efficiently at this epoch. At z ~ 1–1.6, morphological analysis of emission-line galaxies in the COSMOS field investigates how galaxy structure and compactness vary across large-scale environments. At z ~ 2.16, pixel-by-pixel SED fitting of Spiderweb protocluster members reveals clear inside-out quenching in massive quiescent galaxies. At higher redshifts, structural analysis of Lyman-a emitters across z ~ 2–7 from JWST COSMOS-Web reveals systematic size evolution and a significant anticorrelation between compactness and Lya equivalent width. Within this sample, we report the discovery of a protocluster at z ˜ 4.9 with clear wavelength-dependent environmental effects on galaxy morphology. I present spatially resolved Ha morphological analysis of galaxies at z ~ 4–6 with JWST, tracing how star formation structure evolves near the epoch of reionization.