Measuring the Mean and Scatter of the X-Ray Luminosity-Optical Richness Relation for maxBCG Galaxy Clusters
Abstract
Determining the scaling relations between galaxy cluster observables requires large samples of uniformly observed clusters. We measure the mean X-ray luminosity-optical richness (-bar N200) relation for an approximately volume-limited sample of more than 17,000 optically selected clusters from the maxBCG catalog spanning the redshift range 0.1 < z < 0.3. By stacking the X-ray emission from many clusters using ROSAT All-Sky Survey data, we are able to measure mean X-ray luminosities to ~10% (including systematic errors) for clusters in nine independent optical richness bins. In addition, we are able to crudely measure individual X-ray emission from ~800 of the richest clusters. Assuming a lognormal form for the scatter in the LX-N200 relation, we measure σln L = 0.86 +/- 0.03 at fixed N200. This scatter is large enough to significantly bias the mean stacked relation. The corrected median relation can be parameterized by bar LX = eα(bar N200/40)β × 1042 h-2 ergs s-1, where α = 3.57 +/- 0.08 and β = 1.82 +/- 0.05. We find that X-ray-selected clusters are significantly brighter than optically selected clusters at a given optical richness. This selection bias explains the apparently X-ray-underluminous nature of optically selected cluster catalogs.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 2008
- DOI:
- 10.1086/527537
- arXiv:
- arXiv:0709.1158
- Bibcode:
- 2008ApJ...675.1106R
- Keywords:
-
- galaxies: clusters: general;
- X-rays: galaxies: clusters;
- Astrophysics
- E-Print:
- 21 pages, 12 figures, revised after referee's comments. ApJ accepted