Prof Gavin Dalton

Abstract:

We have constructed a new catalog of rich clusters of galaxies by applying an objective selection algorithm to the APM Galaxy Survey. We have measured redshifts for 173 clusters from this catalog leading to a redshift survey of over 200 rich APM clusters with z ≲ 0.1 when we include published redshifts. The mean space density for this subsample is n̄ = 2.4 × 10-5 h3 Mpc 3 ,2i.e., about four times the mean space density of R ≥ 1 Abell clusters. The spatial correlation function for our redshift sample can be approximated by ξcc(s) = (r0/s)2 with r0 = 12.9 ± 1.4 h-1 Mpc. The correlation length for the 93 richest clusters in our sample is r0 = 14 ± 4 h-1 Mpc. These results are consistent with the amplitude for ξcc expected in the standard cold dark matter model on scales ≲10 h-1 Mpc and are lower than the amplitude (r0 ∼ 25 h-1 Mpc) found by Bahcall & Soneira from the Abell catalog. However, our results indicate more clustering than expected in the standard cold dark matter model on scales ≲ 10 h-1 Mpc. We argue that the APM cluster catalog is more homogeneous than the Abell sample, and we demonstrate that our redshift-space correlation function is free from spurious large-scale anisotropies and is compatible with small (≳500 km s-1) cluster peculiar velocities.