X-ray galaxy clusters in NoSOCS: Substructure and the correlation of optical and X-ray properties

P. A.A. Lopes, R. R. De Carvalho, H. V. Capelato, R. R. Gal, S. G. Djorgovski, R. J. Brunner, S. C. Odewahn, A. A. Mahabal

Research output: Contribution to journalArticlepeer-review


We present a comparison of optical and X-ray properties of galaxy clusters in the northern sky, using literature data from BAX and optically selected clusters in DPOSS. We determine the recovery rate of X-ray-detected clusters in the optical as a function of richness, redshift, and X-ray luminosity, showing that the missed clusters are typically low-contrast systems when observed optically (either poor or at high redshifts). We employ four different statistical tests to test for the presence of substructure using optical two-dimensional data. We find that approximately 35% of the clusters show strong signs of substructure in the optical. However, the results are test-dependent, with variations also due to the magnitude range and radius utilized, We have also performed a comparison of X-ray luminosity and temperature with optical galaxy counts (richness). We find that the slope and scatter of the relations between richness and the X-ray properties are heavily dependent on the density contrast of the clusters. The selection of substructurefree systems does not improve the correlation between X-ray luminosity and richness, but this comparison also shows much larger scatter than one obtained using the X-ray temperature. In the latter case, the sample is significantly reduced because temperature measurements are available only for the most massive (and thus high-contrast) systems. However, the comparison between temperature and richness is very sensitive to the exclusion of clusters showing signs of substructure. The correlation of X-ray luminosity and richness is based on the largest sample to date (∼750 clusters), while tests involving temperature use a similar number of objects as previous works (≃100). The results presented here are in good agreement with existing literature.

Original languageEnglish (US)
Pages (from-to)209-229
Number of pages21
JournalAstrophysical Journal
Issue number1 I
StatePublished - Sep 1 2006


  • Catalogs
  • Galaxies: clusters: general
  • X-rays: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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