Color - magnitude sequence in the clusters at z ∼ 1.2 near the radio galaxy 3C 324

Masaru Kajisawa, Toru Yamada, Ichi Tanaka, Toshinori Maihara, Fumihide Iwamuro, Hiroshi Terada, Miwa Goto, Kentaro Motohara, Hirohisa Tanabe, Tomoyuki Taguchi, Ryuji Hata, Masanori Iye, Masatoshi Imanishi, Yoshihiro Chikada, Michitoshi Yoshida, Chris Simpson, Toshiyuki Sasaki, George Kosugi, Tomonori Usuda, Kazuhiro Sekiguchi

Research output: Contribution to journalArticlepeer-review

21 Citations (Scopus)


We have investigated the optical and near-infrared colors of K′-selected galaxies in clusters at z ∼ 1.2 near to the radio galaxy 3C 324 using images obtained with the Subaru telescope and archival HST data. The distribution of colors of the galaxies in the cluster region is found to be fairly broad, and it may imply significant scatter in their star-formation histories, although the effect of contamination of field galaxies is uncertain. The red sequence of galaxies whose R - K colors are consistent with passive evolution models for old galaxies is found to be truncated at K′ ∼ 20 mag, and there are few fainter galaxies with similar red colors in the cluster region. We find that the bulge-dominated galaxies selected by quantitative morphological classification form a broad sequence in the color - magnitude diagram, whose slope is much steeper than that expected from metallicity variations within a passively evolving coeval galaxy population. We argue that the observed color - magnitude sequence can be explained by metallicity and age variations, and the fainter galaxies with K′ > 20 mag may be 1-2 Gyr younger than the brighter galaxies. Some spatial segregation of the color and K′-band luminosity is seen in the sky distribution; the redder and the brighter objects tend to be located near 3C 324.

Original languageEnglish
Pages (from-to)61-72
Number of pages12
JournalPublications of the Astronomical Society of Japan
Issue number1
Publication statusPublished - 2000
Externally publishedYes


  • Galaxies: clusters
  • Galaxies: evolution
  • Galaxies: formation

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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