2003ApJ...585..182B

The mass function of clusters of galaxies is determined from 400 deg² of early commissioning imaging data of the Sloan Digital Sky Survey using ∼300 clusters in the redshift range z=0.1-0.2. Clusters are selected using two independent selection methods: a matched filter and a red-sequence color-magnitude technique. The two methods yield consistent results. The cluster mass function is compared with large-scale cosmological simulations. We find a best-fit cluster normalization relation of σ₈Ω^0.6_m=0.33±0.03 (for 0.1≲Ω_m≲0.4) or, equivalently, σ₈=(0.16/Ω_m)^0.6. The amplitude of this relation is significantly lower than the previous canonical value, implying that either Ω_mis lower than previously expected (Ω_m=0.16 if σ₈=1) or σ₈is lower than expected (σ₈=0.7 if Ω_m=0.3). The shape of the cluster mass function partially breaks this classic degeneracy. We find best-fit parameters of Ω_m=0.19±^0.08_0.07and σ₈=0.9±^0.3_0.2. High values of Ω_m(≳0.4) and low σ₈(≲0.6) are excluded at ≳2 σ.