Clusters in collision?

M. P. Ulmer*, G. D. Wirth, M. P. Kowalski

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

21 Scopus citations


We have determined the positions of the optical and X-ray centers in 13 rich galaxy clusters studied by Dressier. We tested the accuracy and precision of four methods for determining cluster centers: nearestneighbor density, mean, median, and density-weighted mean, the last two proved superior. With the use of bootstrap resampling to obtain accurate confidence intervals on the positions of the centers, we have quantified the significance of the X-ray/optical offsets. Insignificant offsets were found in Abell 119, 154, 376, 400, 539, 1656, 1991, 2063, and 2634. The offset previously found by Snyder et al. in the Perseus cluster (Abell 426) was reproduced in our study but found to be only marginally significant, as were the offsets in Abell 754 and 2256. Abell 168 exhibits an apparently real discrepancy between its visible and X-ray centers, which we interpret as evidence that this cluster (and by implication other clusters) resulted from the collision of two approximately equal sized clusters.

Original languageEnglish (US)
Pages (from-to)430-437
Number of pages8
JournalAstrophysical Journal
Issue number2
StatePublished - 1992


  • Galaxies: clustering
  • X-rays: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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