NIR spectroscopic observation of massive galaxies in the protocluster at z = 3.09

We present the results of near-infrared spectroscopic observations of the K-band-selected candidate galaxies in the protocluster at z = 3.09 in the SSA22 field. We observed 67 candidates with K_AB < 24 and confirmed redshifts of the 39 galaxies at 2.0 < z_spec < 3.4. Of the 67 candidates, 24 are certainly protocluster members with 3.04 ≤ z_spec ≤ 3.12, which are massive red galaxies that have been unidentified in previous optical observations of the SSA22 protocluster. Many distant red galaxies (J - K_AB > 1.4), hyper extremely red objects (J - K_AB > 2.1), Spitzer MIPS 24 μm sources, active galactic nuclei (AGNs) as well as the counterparts of Lyα blobs and the AzTEC/ASTE 1.1 mm sources in the SSA22 field are also found to be protocluster members. The mass of the SSA22 protocluster is estimated to be ∼2-5 × 10¹⁴ M_⊙, and this system is plausibly a progenitor of the most massive clusters of galaxies in the current universe. The reddest (J - K_AB ≥ 2.4) protocluster galaxies are massive galaxies with M_star ∼ 10¹¹ M_⊙ showing quiescent star formation activities and plausibly dominated by old stellar populations. Most of these massive quiescent galaxies host moderately luminous AGNs detected by X-ray. There are no significant differences in the [O III] λ5007/Hβ emission line ratios and [O III] λ5007 line widths and spatial extents of the protocluster galaxies from those of massive galaxies at z ∼ 2-3 in the general field.