A technique for detecting structure in cluster velocity distributions

Ann I. Zabludoff, Marijn Franx, Margaret J. Geller

Research output: Contribution to journalArticlepeer-review

26 Scopus citations


For clusters with ≳ 100 measured galaxy redshifts, we develop a new method for detecting departures from a Gaussian velocity distribution. We decompose the cluster velocity distribution into a sum of the orthogonal Gauss-Hermite functions. This method quantifies the asymmetric third-order (h3) and symmetric fourth-order (h4) terms of the distribution while minimizing the effect of interlopers in the tails. We apply the method to a sample of eight rich clusters: A426, A548, A1060, A1656, A2151, A2670, DC 2048-52, and Centaurus. Each cluster has more than 100 members with known redshifts. The clusters A548, A1656, DC 2048-52, and Centaurus significantly depart from Gaussian. A1656 and DC 2048-52 have asymmetric velocity distributions; A548 and Centaurus have broad, symmetric distributions. The most likely interpretation is that these systems have substructure. This result is consistent with findings by other authors.

Original languageEnglish (US)
Pages (from-to)47-51
Number of pages5
JournalAstrophysical Journal
Issue number1
StatePublished - Dec 10 1993


  • Galaxies: clustering
  • Galaxies: distances and redshifts

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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