Down-sizing in galaxy formation at z ∼ 1 in the Subaru/XMM-Newton deep survey (SXDS)

Tadayuki Kodama, Toru Yamada, Masayuki Akiyama, Kentaro Aoki, Mamoru Doi, Hisanori Furusawa, Tetsuharu Fuse, Masatoshi Imanishi, Cathy Ishida, Masanori Iye, Masaru Kajisawa, Hiroshi Karoji, Naoto Kobayashi, Yutaka Komiyama, George Kosugi, Yoshitomo Maeda, Satoshi Miyazaki, Yoshihiko Mizumoto, Tomoki Morokuma, Fumiaki NkataJunichi Noumaru, Ryusuke Ogasawara, Masami Ouchi, Toshiyuki Sasaki, Kazuhiro Sekiguchi, Kazuhiro Shimasaku, Chris Simpson, Tadafumi Takata, Ichi Tanaka, Yoshihiro Ueda, Naoki Yasuda, Michitoshi Yoshida

Research output: Contribution to journalArticlepeer-review

159 Citations (Scopus)


We use the deep wide-field optical imaging data of the Subaru/XMM-Newton Deep Survey to discuss the luminosity- (mass-)dependent galaxy colours down to z′ = 25.0 (5 × 109 h70-2 M ) for z ∼ 1 galaxies in colour-selected high-density regions. We find an apparent absence of galaxies on the red colour-magnitude sequence below z′ ∼ 24.2, corresponding to ∼M* + 2 (∼ 1010 M) with respect to passively evolving galaxies at z ∼ 1. Galaxies brighter than M* -0.5 (8 × 1010 M), however, are predominantly red passively evolving systems, with few blue star-forming galaxies at these magnitudes. This apparent age gradient, where massive galaxies are dominated by old stellar populations while less massive galaxies have more extended star formation histories, supports the 'down-sizing' idea where the mass of galaxies hosting star formation decreases as the Universe ages. Combined with the lack of evolution in the shape of the stellar mass function for massive galaxies since at least z ∼ 1, it appears that galaxy formation processes (both star formation and mass assembly) should have occurred in an accelerated way in massive systems in high-density regions, while these processes should have been slower in smaller systems. This result provides an interesting challenge for modern cold dark matter based galaxy formation theories which predict later formation epochs of massive systems, commonly referred to as 'bottom-up'.

Original languageEnglish
Pages (from-to)1005-1014
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Publication statusPublished - 2004 May 21


  • Galaxies: clusters: general
  • Galaxies: evolution
  • Galaxies: formation
  • Galaxies: stellar content


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