Dark energy survey year 3 results: mis-centering calibration and X-ray-richness scaling relations in redMaPPer clusters

We use Dark Energy Survey Year 3 (DES Y3) clusters with archival XMM-Newton and Chandra X-ray data to assess the centering performance of the redMaPPer cluster finder and to measure key richness observable scaling relations. We find that 10-20% of redMaPPer clusters are miscentered, both when comparing to the X-ray peak position and to the visually identified central cluster galaxy. We find no significant difference in miscentering in bins of low versus high richness or redshift. The dominant reasons for miscentering include masked or missing data and the presence of other bright galaxies in the cluster; for half of the miscentered clusters the correct central was one of the possible centrals identified by redMaPPer, while for ∼40% of miscentered clusters the correct central is not a redMaPPer member mostly due to masking. Additionally, we fit scaling relations of X-ray temperature and luminosity with richness. We find a TX-λ scatter of 0.21 ± 0.01. While the scatter in TX-λ is consistent in redshift bins, we find modestly different slopes with high-redshift clusters displaying a somewhat shallower relation. Splitting based on richness, we find a marginally larger scatter for our lowest richness bin, 20 < λ < 40. We note that the robustness of the scaling relations at lower richnesses are limited by the unknown selection function, but at λ > 75 we detect nearly all of the clusters falling within existing X-ray pointings. The X-ray properties of detected, serendipitous clusters are generally consistent with those of targeted clusters.