A Detailed Study of Massive Galaxies in a Protocluster at z = 3.13

We present a detailed study of near-IR selected galaxies in a protocluster field at z = 3.13. Protocluster galaxies are selected using the available mutliwavelength data with the photometric redshifts (photo-z) at 2.9 < z < 3.3, reaching a mass completeness of $\simeq {10}^{10}\,{M}_{\odot }$ . Diverse types of galaxies have been found in the field, including normal star-forming galaxies, quiescent galaxies, and dusty star-forming galaxies. The photo-z galaxies form two large overdense structures in the field, largely overlapping with the previously identified galaxy overdensities traced by Lyα emitters (LAEs) and Lyman break galaxies, respectively. The northern overdensity consists of a large fraction of old and/or dusty galaxy populations, while the southern one is mainly composed of normal star-forming galaxies that are spatially correlated with the LAEs. This agrees with our previous study arguing the spatial offset of different galaxy overdensities may be due to halo assembly bias. Given the large end-to-end sizes of the two overdensities, one possibility is that they will form into a supercluster by the present day. We also find strong evidence that the star formation activities of the galaxies in the overdense protocluster regions are enhanced in comparison to their field counterparts, which suggests an accelerated mass assembly in this protocluster.