2014ApJ...783...80R

We evaluate the performance of the Sloan Digital Sky Survey (SDSS) DR8 redMaPPer photometric cluster catalog by comparing it to overlapping X-ray- and Sunyaev-Zeldovich (SZ)-selected catalogs from the literature. We confirm that the redMaPPer photometric redshifts are nearly unbiased ( < Δz > ≤ 0.005), have low scatter (σ_z~ 0.006-0.02, depending on redshift), and have a low catastrophic failure rate (~1%). Both the T_X-λ and M_gas-λ scaling relations are consistent with a mass scatter of σ_ ln M|λ_~ 25%, albeit with a ~1% outlier rate due to projection effects (λ is the cluster richness estimated employed by redMaPPer). This failure rate is somewhat lower than that expected for the full cluster sample but is consistent with the additional selection effects introduced by our reliance on X-ray and SZ selected reference cluster samples. Where the redMaPPer DR8 catalog is volume-limited (z ≤ 0.35), the catalog is 100% complete above T_X ≳ 3.5 keV, and L_X ≳ 2x10⁴⁴ erg/s, decreasing to 90% completeness at L_X~ 10⁴³ erg/s. All rich (λ ≳ 100), low-redshift (z ≲ 0.25) redMaPPer clusters are X-ray-detected in the ROSAT All Sky Survey, and 86% of the clusters are correctly centered. Compared to other SDSS photometric cluster catalogs, redMaPPer has the highest completeness and purity, and the best photometric redshift performance, though some algorithms do achieve comparable performance to redMaPPer in subsets of the above categories and/or in limited redshift ranges. The redMaPPer richness is clearly the one that best correlates with X-ray temperature and gas mass. Most algorithms (including redMaPPer) have very similar centering performance as tested by comparing against X-ray centers, with only one exception which performs worse.