(Proposal ID) S15A-025 (PI) Ogura, Kazuyuki (Proposal Title) A search for missing over-density regions through high-z damped Lyalpha systems (Abstract) Studying the formation and evolution of galaxies and large-scale structures is one of the hottest topics, and specifically the identification of high-z over- density regions is interesting to study the structure formation. However, previous searches for high-z over-density regions are based on the detection of the number excess of star-forming galaxies. Therefore we are possibly missing high-z over-density regionsif the most of baryons in those systems are still in the gas-phase (i.e., lacking detectable amount of stars). For identifying such "missing'' over-density regions, we focus on damped Lyalpha (DLA) systems.Thanks to the recent progress of the BOSS Survey, >10^4 DLAs are recognized now. Based on the BOSS DLA sample, we found two interesting fields where some DLAs are clustered in both angular and redshift directions. Here we propose to obtain deep NB400 and broad-band images with Suprime-Cam for those 2 regions, aiming at: (1) identifying the DLA counterparts at z~ 2.3 in the target fields by searching for NB400-excess objects around the background quasars, (2) surveying Lyalpha emitters in the target fields to search for over-density regions traced originally by DLAs, and (3) characterizing the DLA counterparts and surrounding LAEs by combining the NB400 and broad-band magnitudes.