The formation of the massive galaxies in the SSA22 z = 3.1 protocluster
- Astronomical Institute, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai, Miyagi, 980-8578 (Japan)
- Research Center for Space and Cosmic Evolution, Ehime University, Bunkyo-cho 2-5, Matsuyama 790-8577 (Japan)
- Chile Observatory, National Astronomical Observatory of Japan, Tokyo 181-8588 (Japan)
- Research Center for Neutrino Science, Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai, Miyagi, 980-8578 (Japan)
- Institute of Astronomy, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo, 181-0015 (Japan)
- Subaru Telescope, National Astronomical Observatory of Japan, 650 North Aohoku Place, Hilo, HI 96720 (United States)
- Koyama Astronomical Observatory, Kyoto Sangyo University, Motoyama, Kamigamo, Kita-ku, Kyoto 603-8555 (Japan)
- Department of Physics, Durham University, Durham DH1 3LE (United Kingdom)
- Center for Astrophysics, Cambridge, MA 02138 (United States)
- The Johns Hopkins University, Homewood Campus, Baltimore, MD 21218 (United States)
We study the properties of K-band-selected galaxies (K {sub AB} < 24) in the z = 3.09 SSA22 protocluster field. 430 galaxies at 2.6 < z {sub phot} < 3.6 are selected as potential protocluster members in a 112 arcmin{sup 2} area based on their photometric redshifts. We find that ≈20% of the massive galaxies with stellar masses >10{sup 11} M {sub ☉} at z {sub phot} ∼ 3.1 have colors consistent with those of quiescent galaxies with ages >0.5 Gyr. This fraction increases to ≈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 μm sources at z {sub phot} ∼ 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 (AGNs) is also high compared with the field. The sky distribution of the quiescent galaxies, the 24 μm sources, and the X-ray AGNs show clustering around a density peak of z = 3.1 Lyα emitters. A significant fraction of the massive galaxies have already become quiescent, while 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 in the centers of the predecessors to present-day rich galaxy clusters.
- OSTI ID:
- 22341900
- Journal Information:
- Astrophysical Journal, Vol. 778, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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