Previous protocluster surveys, including our various programs in the past, successfully revealed protocluster structures and star formation of member galaxies, and hence the mass assembly at z<2.6. However, an early phase of cluster formation at z>3 is still poorly investigated, especially because Hα line is no longer observable from the ground. In that context, we propose a 2-night for MOIRCS/NB2083,J,Ks-band imaging to perform a panoramic mapping of [Oiii] emitters associated with a valuable protocluster at z=3.16. Luckily, our custom-made narrowband filter greatly covers the redshift range of this very-unique protocluster system. Our program is designed to (1) unveil the protocluster structure and substructures as demonstrated by previous Hα narrowband surveys at z<2.6 and (2) identify ionizing sources of an enormous Lyα nebula associated with the protocluster. Notably, the target protocluster hosts the largest Lyα nebula at z>3 discovered to date, termed “Fabulous Nebula". Its Lyα kinematics shows a signature of the inspiraling cold streams, which are feeding mechanisms of cold gas feeding and build-up of angular momentum in protocluster haloes. Therefore, this program will provide us with unique insights into galaxy growth in the early phase of galaxy clusters.
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