4.6 Article

A study of catalogued nearby galaxy clusters in the SDSS-DR4 II. Cluster substructure

Journal

ASTRONOMY & ASTROPHYSICS
Volume 521, Issue -, Pages -

Publisher

EDP SCIENCES S A
DOI: 10.1051/0004-6361/200913901

Keywords

galaxies: clusters: general

Funding

  1. Alfred P. Sloan Foundation
  2. National Science Foundation
  3. US Department of Energy
  4. National Aeronautics and Space Administration
  5. Japanese Monbukagakusho
  6. Max Planck Society
  7. Higher Education Funding Council for England
  8. American Museum of Natural History
  9. Astrophysical Institute Potsdam
  10. University of Basel
  11. Cambridge University
  12. Case Western Reserve University
  13. University of Chicago
  14. Drexel University
  15. Fermilab
  16. Institute for Advanced Study
  17. Japan Participation Group
  18. Johns Hopkins University
  19. Joint Institute for Nuclear Astrophysics
  20. Kavli Institute for Particle Astrophysics and Cosmology
  21. Korean Scientist Group
  22. Chinese Academy of Sciences (LAMOST)
  23. Los Alamos National Laboratory
  24. Max-Planck-Institute for Astronomy (MPIA)
  25. Max-Planck-Institute for Astrophysics (MPA)
  26. New Mexico State University
  27. Ohio State University
  28. University of Pittsburgh
  29. University of Portsmouth
  30. Princeton University
  31. United States Naval Observatory
  32. University of Washington
  33. [AYA2007-67965-C03-01]

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Context. According to the current cosmological paradigm, large scale structures form hierarchically in the Universe. Clusters of galaxies grow through a continuous accretion of mass, and the presence of cluster substructures can be interpreted as signature of this process. Nevertheless, the rate and manner of mass accretion events are still matters of debate. Aims. We have analysed the presence of substructures in one of the largest sample of nearby cluster galaxies available in the literature. We have determined the fraction of clusters with substructure and the properties of the galaxies located in such substructures. Methods. Substructure in the galaxy clusters was studied using the Dressler-Shectman test, which was calibrated through extensive Monte Carlo simulations of galaxy clusters similar to real ones. In order to avoid possible biases in the results due to differing incompleteness among clusters, we selected two galaxy populations: a) galaxies brighter than M-r = -20 located in clusters at z < 0.1 (EC1); and b) galaxies of brightness M-r < -19 located at z < 0.07 (EC2). Results. In the inner cluster regions (r < r(200)) 11% and 33% of the clusters of EC1 and EC2 respectively show substructure. This fraction is larger in the outer cluster regions (approximate to 55%) for EC1 and EC2 samples. Cluster global properties, such as sigma(c), f(b) or Delta m(12) do not depend on the amount of cluster substructure. We have studied the properties of individual galaxies located in substructures in the EC1 and EC2 galaxy populations. The fraction of galaxies within substructures is larger in the outer cluster regions when fainter galaxies are included. The distribution of relative velocities of galaxies within substructures suggest that they consist of an infalling population mixed with backsplash galaxies. We can not rule out that the infalling galaxy population located in substructures are genuine field ones.

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