2017MNRAS.469.2235K

We present the near-infrared high-resolution imaging of an extremely dense group of galaxies at the core of the protocluster at z = 3.09 in the SSA22 field by using the adaptive optics AO188 and the Infrared Camera and Spectrograph on board the Subaru Telescope. The wide morphological variety of them suggests their ongoing dramatic evolutions. One of the two quiescent galaxies (QGs), the most massive one in the group, is a compact elliptical with an effective radius r_e = 1.37 ± 0.75 kpc. It supports the two-phase formation scenario of giant ellipticals today that a massive compact elliptical is formed at once and evolves in size and stellar mass by a series of mergers. Since this object is a plausible progenitor of a brightest cluster galaxy of one of the most massive clusters today, it requires strong size ( >= 10) and stellar mass (∼ four times by z = 0) growths. Another QG hosts an active galactic nucleus and is fitted with a model composed from a nuclear component and Sersic model. It shows a spatially extended [O III] λ5007 emission line compared to the continuum emission, plausible evidence of outflows. Massive star-forming galaxies (SFGs) in the group are two to three times larger than the field SFGs at similar redshift. Although we obtained the K-band image deeper than the previous one, we found no new candidate members. This implies a physical deficiency of low-mass galaxies with stellar mass M_* <= 4 x 10¹⁰ M_☉ and/or poor detection completeness of them owing to their diffuse morphologies.