High Lyman Continuum Escape Fraction in a Lensed Compact Dwarf Galaxy at Z=2.5

Reionization is the process that reionized the matter in the Universe. It is one of major phase transitions of gas in the universe. Galaxies are considered the major source to provide the ionizing photons and reionize the Universe. However, there is a key parameter, the fraction of ionizing photons (a.k.a., Lyman Continuum, LyC) that can escape from galaxies, which has not been well constrained. There are less than 10 galaxies whose LyC emissions are detected. In this talk, I will report an HST UV imaging survey to search for LyC emission in a sample of lensed galaxies at z=2-3. We firmly detect LyC emission in a compact dwarf galaxy, A2218-Flanking. The absolute LyC escape fraction of A2218-Flanking is greater than 50%. In this talk, I will discuss how the LyC escape fraction changes across the galaxy using the supreme spatial resolution of HST images, which will shed light on the dominate physical process to drive the large LyC escape fraction.