Richness limits of the survey. The black curves show the 90% (dashed) and 50% (dotted) completeness limits P^SDSS of redMaPPer cluster confirmation via SDSS data (Rykoff et al. 2014). The gray curves indicate the 10% (solid), 50% (long-dashed) and 90% (short-dashed) completeness limits of the RASS. The 10% curve also serves as a limit for low (5%, Klein et al. 2019) contamination subsample and is adopted as our selection P^RASS.