Astronomy Colloquium / Fall 2007

October 31

Dr. Erin Sheldon

NYU

Cluster Lensing in the SDSS

I'll talk about weak lensing measurements around galaxy clusters in the Sloan Digital Sky Survey. We use the MaxBCG cluster catalog, assembled from SDSS photometric data, containing ~13,000 clusters with mass greater than 5x1013 solar masses, and many more smaller objects. The mean mass profiles for clusters binned by richness are consistent with a universal NFW profile. On much larger scales (~30Mpc), the profiles are consistent with linear correlations between halos and the mass field, favoring low sigma-8. The mass-to-light ratio (M/L) is an increasing function of cluster-centric distance, and the M/L within the virial radius increases with cluster richness. The M/L approaches a constant value at very large radius, independent of cluster richness. Interpreted in terms of the universal M/L this yields a measure of omega matter, independent of the hubble parameter.