Cosmic Mammoth - Map the Most Massive Large-scale Structures in early Universe

In this talk, I will present a novel survey of the most massive overdensities of galaxies at z=2-3, traced by strongest IGM HI (Lyman-alpha) absorption on large scales of 10-30 Mpc. Our cosmological simulations show a strong correlation between the optical depth of Ly-alpha absorption and mass overdensities on 10-30 Mpc. I will show techniques to search for the strongest Ly-alpha absorption due to IGM overdensities, and further present our follow-up imaging and LBT, Keck spectroscopic observations on a sample of extremely overdensies at z~2.3, anchored by strongest IGM Ly-alpha absorption. I will further discuss the giant/enormous Lyman alpha nebulae discovered in these fields. One of these Lyman alpha nebulae have the largest spatial extent found up to date. In the end, I will talk about the future prospects, and discuss a few exciting prospects that can be done in collaborating with PKU/KIAA's world experts, by utilizing this and next generation telescopes and surveys.