The Correlation Function of Flux-limited X-ray Clusters
نویسنده
چکیده
We show that the spatial correlation function of a flux-limited sample of Xray selected clusters of galaxies will exhibit a correlation scale that is smaller than the correlation scale of a volume-limited, richness-limited sample of comparable apparent spatial density. The flux-limited sample contains clusters of different richnesses at different distances: poor groups are found nearby and rich clusters at greater distances. Since the cluster correlation strength is known to increase with richness, the flux-limited sample averages over the correlations of poor and rich clusters. On the other hand, a volume-limited, richness-limited sample has a minimum richness threshold, and a constant mixture of richnesses with redshift. Using the observed correlation scale for rich (R ≥ 1) clusters, ro(R ≥ 1) = 21± 2hMpc that was determined from previous volume-limited studies, we derive for the ROSAT flux-limited X-ray cluster sample ro(flux−limited) ≈ 14h Mpc, in agreement with the recently observed value of 13.7± 2.3hMpc. Cosmology: large-scale structure of Universe – galaxies: clusters of – X-rays: galaxies
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