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arXiv · 1310.2020

The Formation of the massive galaxies in the SSA22 z=3.1 protocluster

Mariko Kubo·Yuka Katsuno Uchimoto·Toru Yamada·Masaru Kajisawa·Takashi Ichikawa·Yuichi Matsuda·Masayuki Akiyama·Tomoki Hayashino·Masahiro Konishi·Tetsuo Nishimura·Koji Omata·Ryuji Suzuki·Ichi Tnaka·Tomohiro Yoshikawa·David. M. Alexander·Giovanni. G. Fazio·J. -S. Huang·Bret. D. Lehmer
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Abstract

The properties of K-band selected galaxies (K_AB<24) in the z = 3.09 SSA22 protocluster field are studied. 430 galaxies at 2.6 < z_phot < 3.6 are selected as potential protocluster members in a 112 arcmin^2 area based on their photometric redshifts. We find that \approx 20% of the massive galaxies with stellar masses >10^11 M_sun at z_phot \sim 3.1 have colors consistent with those of quiescent galaxies with ages > 0.5 Gyr. This fraction increases to \approx 50% after correcting for unrelated foreground/background objects. We also find that 30% of the massive galaxies are heavily reddened dusty star-forming galaxies. Few such quiescent galaxies at similar redshifts are seen in typical survey fields. An excess surface density of 24\mu m sources at z_phot \sim 3.1 is also observed, implying the presence of dusty star-formation activity in the protocluster. Cross-correlation with the X-ray data indicates that the fraction of K-band selected protocluster galaxies hosting active galactic nuclei (AGN) is also high compared with the field. The sky distribution of the quiescent galaxies, the 24\mu m sources, and the X-ray AGNs show clustering around a density peak of z=3.1 Ly\alpha emitters (LAEs). A significant fraction of the massive galaxies have already become quiescent, while the dusty star-formation is still active in the SSA22 protocluster. These findings indicate that we are witnessing the formation epoch of massive early-type galaxies at the center of predecessors to present-day rich galaxy clusters.

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Mariko Kubo, Yuka Katsuno Uchimoto, Toru Yamada, Masaru Kajisawa, Takashi Ichikawa, Yuichi Matsuda, Masayuki Akiyama, Tomoki Hayashino, Masahiro Konishi, Tetsuo Nishimura, Koji Omata, Ryuji Suzuki, Ichi Tnaka, Tomohiro Yoshikawa, David. M. Alexander, Giovanni. G. Fazio, J. -S. Huang, Bret. D. Lehmer. 2013-10-08. The Formation of the massive galaxies in the SSA22 z=3.1 protocluster. https://doi.org/10.1088/0004-637x/778/2/170

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