We use the abundance and weak lensing mass measurements of the SDSS maxBCG cluster catalog to simultaneously constrain cosmology and the richness–mass relation of the clusters .
Assuming a flat \Lambda CDM cosmology , we find \sigma _ { 8 } ( \Omega _ { m } / 0.25 ) ^ { 0.41 } = 0.832 \pm 0.033 after marginalization over all systematics .
In common with previous studies , our error budget is dominated by systematic uncertainties , the primary two being the absolute mass scale of the weak lensing masses of the maxBCG clusters , and uncertainty in the scatter of the richness–mass relation .
Our constraints are fully consistent with the WMAP five-year data , and in a joint analysis we find \sigma _ { 8 } = 0.807 \pm 0.020 and \Omega _ { m } = 0.265 \pm 0.016 , an improvement of nearly a factor of two relative to WMAP5 alone .
Our results are also in excellent agreement with and comparable in precision to the latest cosmological constraints from X-ray cluster abundances .
The remarkable consistency among these results demonstrates that cluster abundance constraints are not only tight but also robust , and highlight the power of optically-selected cluster samples to produce precision constraints on cosmological parameters .