Evolution of the early-type galaxy fraction in clusters since z = 0.8

L. Simard, D. Clowe, V. Desai, J. J. Dalcanton, A. Von Der Linden, B. M. Poggianti, S. D.M. White, A. Aragón-Salamanca, G. De Lucia, C. Halliday, P. Jablonka, B. Milvang-Jensen, R. P. Saglia, R. Pelló, G. H. Rudnick, D. Zaritsky

Research output: Contribution to journalArticlepeer-review

46 Scopus citations


We study the morphological content of a large sample of high-redshift clusters to determine its dependence on cluster mass and redshift. Quantitative morphologies are based on PSF-convolved, 2D bulge+disk decompositions of cluster and field galaxies on deep Very Large Telescope FORS2 images of eighteen, optically-selected galaxy clusters at 0.45 < z < 0.80 observed as part of the ESO Distant Cluster Survey ("EDisCS"). Morphological content is characterized by the early-type galaxy fraction fet, and early-type galaxies are objectively selected based on their bulge fraction and image smoothness. This quantitative selection is equivalent to selecting galaxies visually classified as E or S0. Changes in early-type fractions as a function of cluster velocity dispersion, redshift and star-formation activity are studied. A set of 158 clusters extracted from the Sloan Digital Sky Survey is analyzed exactly as the distant EDisCS sample to provide a robust local comparison. We also compare our results to a set of clusters from the Millennium Simulation. Our main results are: (1) the early-type fractions of the SDSS and EDisCS clusters exhibit no clear trend as a function of cluster velocity dispersion. (2) Mid-z EDisCS clusters around σ = 500 km s-1 have f et ∼ 0.5 whereas high-z EDisCS clusters have fet ∼ 0.4. This represents a ̃25% increase over a time interval of 2 Gyr. (3) There is a marked difference in the morphological content of EDisCS and SDSS clusters. None of the EDisCS clusters have early-type galaxy fractions greater than 0.6 whereas half of the SDSS clusters lie above this value. This difference is seen in clusters of all velocity dispersions. (4) There is a strong and clear correlation between morphology and star formation activity in SDSS and EDisCS clusters in the sense that decreasing fractions of [OII] emitters are tracked by increasing early-type fractions. This correlation holds independent of cluster velocity dispersion and redshift even though the fraction of [OII] emitters decreases from z ̃ to z ̃ in all environments. Our results pose an interesting challenge to structural transformation and star formation quenching processes that strongly depend on the global cluster environment (e.g., a dense ICM) and suggest that cluster membership may be of lesser importance than other variables in determining galaxy properties.

Original languageEnglish (US)
Pages (from-to)1141-1159
Number of pages19
JournalAstronomy and astrophysics
Issue number3
StatePublished - Dec 4 2009


  • Galaxies: Fundamental parameters
  • Galaxies: clusters: general
  • Galaxies: evolution

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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