Galaxy Evolution Within and Beyond Clusters: Environmental Effects in Clusters and Lyman-continuum Escape from a Strongly Lensed Galaxy

Galaxy clusters offer unique laboratories for driving our understanding of galaxy evolution. On the first topic, I will show how environmental effects act in distant Universe where such effects still remain elusive. Spanning a wide range of redshift (~5 Gyr, 0.3 < z < 1.1), we investigate a large sample of 1626 cluster galaxies located within 105 clusters. We find clear evidence for a gradual (mean stellar) age increase of galaxies since their in-fall (using projected phase-space). This suggests that galaxies become environmentally quenched due to long exposure to cluster environments such as starvation and/or ram pressure stripping. On the second topic, I will show how Lyman-continuum (LyC) photons escape from a star-forming galaxy, a key unknown process for reionization. The sample galaxy (aka, Sunburst Arc at z=2.4) reveals the exceptionally small scale (tens of parsec) physics of LyC escape thanks to a unique combination of HST’s sharp imaging with strong lensing magnification. We find the remarkably extreme properties of the LyC leaking region such as very blue UV-continuum slope (=-2.9), high ionization state ([O III]/[O II] = ~11), and high Lyman-alpha escape fraction (=0.5). Our findings would suggest that highly ionized, compact star-forming regions with little dust promote the escape of LyC photons in a galaxy.