Luminous Red Galaxy Population in Clusters at 0.2≤ z ≤0.6

Abstract

We investigate statistical properties of luminous red galaxies (LRGs) in a sample of X-ray-selected galaxy clusters at intermediate redshift (0.2 ≤ z ≤ 0.6) of mass range from ~1 × 10^(14) M_☉ to ~8 × 10^(14) M_☉ . The LRGs are selected based on carefully designed color criteria, and the cluster membership is assessed via photometric redshifts. As clusters and LRGs are both viewed as promising tracer of the underlying dark matter distribution, understanding the distribution of LRGs within clusters is an important issue. Our main findings include (1) the halo occupation distribution (HOD) of LRGs inside our cluster sample is N(M) = k(M/10^(14) h^(–1) M_☉)^a , where a = 0.495 ± 0.105 and k = 1.455 ± 0.285 assuming a Poisson distribution for N(M). If we assume the form of N(M) = 1 + k(M/10^(14) h^(–1)M_☉) a , where a = 0.580 ± 0.130 and k = 0.975 ± 0.240 assuming a Poisson distribution for N(M). (2) The HOD of LRGs [N(M)] and the satellite distribution of LRGs [N(M) – 1] are both consistent with being Poisson. To be more quantitative, we find Var(N)/N = 1.43 ± 0.35 and Var(N – 1)/(N – 1) = 1.82 ± 0.50. (3) The radial profile of LRGs within clusters when fitted with a Navarro-Frenk-White profile gives a concentration of 17.5^(+7.1)_(–4.3) (6.0^(+3.2)_(–1.9)) including (excluding) brightest LRGs (BLRGs). In essence, the BLRGs are more concentrated toward the center of the clusters than the other LRGs in clusters. We also discuss the implications of these observations on the evolution of massive galaxies in clusters.

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