The Angular Clustering of Distant Galaxy Clusters

Abstract

We discuss the angular clustering of galaxy clusters at -->z > 1 selected within 50 deg2 from the Spitzer Wide-Infrared Extragalactic survey. We use a simple color selection to identify high-redshift galaxies with no dependence on galaxy rest-frame optical color using Spitzer IRAC 3.6 and 4.5 μm photometry. The majority (>90%) of galaxies with -->z > 1.3 are identified with ( -->[3.6] − [4.5])AB > − 0.1 mag. We identify candidate galaxy clusters at -->z > 1 by selecting overdensities of ≥26-28 objects with -->[3.6] − [4.5] > − 0.1 mag within radii of -->1.4', which corresponds to -->r z = 1.5. These candidate galaxy clusters show strong angular clustering, with an angular correlation function represented by -->w(θ ) = (3.1 ± 0.5)(θ/1')−1.1 ± 0.1 over scales of -->2'- -->100'. Assuming the redshift distribution of these galaxy clusters follows a fiducial model, these galaxy clusters have a spatial-clustering scale length -->r0 = 22.4 ± 3.6 h−1 Mpc and a comoving number density -->n = 1.2 ± 0.1 × 10−5 -->h3 Mpc−3. The correlation scale length and number density of these objects are comparable to those of rich galaxy clusters at low redshift. The number density of these high-redshift clusters corresponds to dark matter halos larger than -->(3–5) × 1013 -->h−1 -->M☉ at -->z = 1.5. Assuming the dark halos hosting these high-redshift clusters grow following ΛCDM models, these clusters will reside in halos larger than -->(1–2) × 1014 -->h−1 -->M☉ at -->z = 0.2, comparable to rich galaxy clusters.