Proto-clusters are thought to develop at intersections of filamentary large-scale structures at high redshifts. A rich proto-cluster HS1700+64 at z=2.3 has the unique two-filament-crossing structure traced by 7 Lyα blobs (LABs). A recent study found that Lyα emitters are distributed so as to avoid the dense regions of Hα emitters in the HS1700. It suggests the potential presence of dense HI gas in the proto-cluster core. However, it depends not only on the HI gas in and around the member galaxies but also on the amount of dust. To mitigate the impact of dust, we propose deep Keck/MOSFIRE spectroscopy to remove the dust extinction effect from the Lyα/Hα ratio, allowing us for the first time to securely identify the surrounding HI gas. Furthermore, we investigate the potential power sources of the LABs, and also possible enhancement of AGN activities in proto-cluster environment by spectroscopically identifying AGNs. We also study the interstellar medium properties of galaxies such as gaseous metallicities. In summary, we investigate the HII gas distribution and the environmental effects, which are critical to understanding the gas accretion and star formation activities in proto-cluster in a vigorous assembly phase.
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