The cluster mass function from early sloan digital sky survey data: Cosmological implications

The mass function of clusters of galaxies is determined from 400 deg(2) of early commissioning imaging data of the Sloan Digital Sky Survey using approximate to 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 sigma(8)Omega(m)(0.6)=0.33+/-0.03 (for 0.1less than or similar toOmega(m)less than or similar to0.4) or, equivalently, sigma(8)=(0.16/Omega(m))(0.6). The amplitude of this relation is significantly lower than the previous canonical value, implying that either Omega(m) is lower than previously expected (Omega(m)=0.16 if sigma(8)=1) or sigma(8) is lower than expected (sigma(8)=0.7 if Omega(m)=0.3). The shape of the cluster mass function partially breaks this classic degeneracy. We find best-fit parameters of Omega(m)=0.19+/-(0.08)(0.07) and sigma(8)=0.9+/-(0.3)(0.2). High values of Omega(m)(greater than or similar to0.4) and low sigma(8)(less than or similar to0.6) are excluded at greater than or similar to2 sigma.