X-Ray Galaxy Clusters in NoSOCS: Substructure and the Correlation of Optical and X-Ray Properties

• Published in: The Astrophysical journal 2006-09, Vol.648 (1), p.209-229
• Main Authors: Lopes, P. A. A, de Carvalho, R. R, Capelato, H. V, Gal, R. R, Djorgovski, S. G, Brunner, R. J, Odewahn, S. C, Mahabal, A. A
• Format: Article
• Language: English
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/505630

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 substructure-free 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 (6 750 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.