redMaPPer - III. A detailed comparison of the Planck 2013 and SDSS DR8 redMaPPer cluster catalogues

We compare the Planck Sunyaev-Zeldovich (SZ) cluster sample (PSZ1) to the Sloan Digital Sky Survey (SDSS) redMaPPer catalogue, finding that all Planck clusters within the redMaPPer mask and within the redshift range probed by redMaPPer are contained in the redMaPPer cluster catalogue. These common clusters define a tight scaling relation in the richness-SZ mass (lambda-M-SZ) plane, with an intrinsic scatter in richness of sigma(lambda vertical bar MSZ) = 0.266 +/- 0.017. The corresponding intrinsic scatter in true cluster halo mass at fixed richness is approximate to 21 per cent. The regularity of this scaling relation is used to identify failures in both catalogues. The failure rates for redMaPPer and PSZ1 1.2 per cent and 14.7 per cent, respectively. The PSZ1 failure rates decreases to 9.8 per cent after removing incorrect redshifts that were drawn from the literature. We note the failure rates in the PSZ1 from this analysis are specific to the SDSS overlap region, and may not be indicative of failure rates over the full Planck survey. We have further identified five PSZ1 sources that suffer from projection effects (multiple rich systems along the line of sight of the SZ detection) and 17 new high-redshift (z greater than or similar to 0.6) cluster candidates of varying degrees of confidence.