Abstract

Cosmic reionization was one of the major phase transitions in the early Universe, and large efforts have been made in the last decade to put constraints on the history of the reionization process. The redshift evolution of the Lya emitter (LAE) fraction has been used to probe the HI gas fraction of the inter-galactic medium at the end of reionization. Recently, some studies have suggested a more moderate evolution of LAE fraction (e.g., De Barros et al. 2017; Pentericci et al. 2018) than previously reported (e.g., Stark et al. 2011; Tilvi et al. 2014). These measurements and their interpretation are still debated strongly. To obtain a firm conclusion, we have to construct an unbiased sample and measure Lya homogeneously over a wide redshift range. In this talk, I will present new results combining deep HST and MUSE data in the Hubble Ultra Deep Field. Our UV-selected galaxies with photometric redshifts from z~3 to 6 are the first UV-complete sample used to study the LAE fraction. We measured the Lya emission of galaxies with the deep IFU data from the MUSE HUDF survey (e.g., Bacon et al. 2017, 2020 in prep.) and investigated the evolution of LAE fraction and implication for the reionization. In addition, I will introduce the MUSE eXtreme deep field  (MXDF; Bacon et al. in prep.) and the latest results on extended Lya emission with more than 100-hour MUSE integration.