We present the results of our near-infrared spectroscopic observations of a rich cluster candidate around a radio galaxy at z = 1.52 (4C65.22) with Subaru/MOIRCS and Large binocular telescope/LUCI. We observed 71 galaxies mostly on the star-forming main sequence selected by our previous broadband (photo-z) and narrowband Hα imaging observation in this cluster environment. We successfully confirmed the redshifts of 39 galaxies, and concluded that this is a gravitationally bound, real cluster at z = 1.517. Our spectroscopic data also suggest a hint of large-scale filaments or sheet-like three-dimensional structures crossing at the highest-density cluster core. By stacking the spectra to derive their average interstellar medium gas-phase metallicity based on the [N ii]/Hα emission line flux ratio, we find that the mass-metallicity relation (MZR) in the 4C65.22 cluster environment is consistent with that of Hα-selected field galaxies at similar redshifts. Our results suggest that the environmental impacts on the MZR is small at high redshifts, but a larger sample of high-z clusters and their member galaxies is still required to fully address the effect of environment as well as its cluster-cluster variation.
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