Understanding the relationship between the Inter-Galactic Medium (IGM) and galaxies is one of the next big frontiers in studying of the galaxy formation and cosmology. In this talk, I will present a survey of the most massive overdensities of galaxies in the peak of cosmic star formation and QSO activities (z=2--4). These structures are traced by the strongest intergalactic Hi (Lyman-alpha) absorption on large scales of 10-30 Mpc. I will present the survey of the extremely massive overdensities at z~2.3 traced by these IGM Lya absorption using Keck, LBT, KPNO-4m, and CFHT. Further, I will discuss the discovery of largest and most luminous Lyman alpha nebulae in these fields, which are unique laboratories to study the IGM-galaxy interactions. Then, I will present our newest observations of these Lyman alpha nebulae using Keck and Palomar Cosmic Web Imager (CWI) and possible evolution of the QSO CGM from z=3 to z=2. In the end, I will talk about the future prospects and highlight a few projects.

Bio
Zheng Cai is a Hubble Fellow at UCSC. He got his Ph.D. degree in the year of 2015 from University of Arizona, and B.S in 2008 at University of Science and Technology of China.