ROBUST OPTICAL RICHNESS ESTIMATION WITH REDUCED SCATTER
- E. O. Lawrence Berkeley National Lab, 1 Cyclotron Rd., Berkeley, CA 94720 (United States)
- Department of Astronomy and Astrophysics, The University of Chicago, Chicago, IL 60637 (United States)
- Center for Particle Astrophysics, Fermi National Accelerator Laboratory, Batavia, IL 60510 (United States)
- Physics Department, University of Michigan, Ann Arbor, MI 48109 (United States)
- UCOLick/Department of Astronomy and Astrophysics, University of California Santa Cruz, Santa Cruz, CA 95064 (United States)
- Kavli Institute for Particle Astrophysics and Cosmology Stanford, CA 94305 (United States)
Reducing the scatter between cluster mass and optical richness is a key goal for cluster cosmology from photometric catalogs. We consider various modifications to the red-sequence-matched filter richness estimator of Rozo et al. implemented on the maxBCG cluster catalog and evaluate the impact of these changes on the scatter in X-ray luminosity (L{sub X} ) at fixed richness, using L{sub X} from the ROSAT All-Sky Catalog as the best mass proxy available for the large area required. Most significantly, we find that deeper luminosity cuts can reduce the recovered scatter, finding that {sigma}{sub ln{sub L{sub x|{lambda}}}}=0.63{+-}0.02 for clusters with M{sub 500c} {approx}> 1.6 Multiplication-Sign 10{sup 14} h{sup -1}{sub 70} M{sub Sun }. The corresponding scatter in mass at fixed richness is {sigma}{sub lnM|{lambda}} Almost-Equal-To 0.2-0.3 depending on the richness, comparable to that for total X-ray luminosity. We find that including blue galaxies in the richness estimate increases the scatter, as does weighting galaxies by their optical luminosity. We further demonstrate that our richness estimator is very robust. Specifically, the filter employed when estimating richness can be calibrated directly from the data, without requiring a priori calibrations of the red sequence. We also demonstrate that the recovered richness is robust to up to 50% uncertainties in the galaxy background, as well as to the choice of photometric filter employed, so long as the filters span the 4000 A break of red-sequence galaxies. Consequently, our richness estimator can be used to compare richness estimates of different clusters, even if they do not share the same photometric data. Appendix A includes 'easy-bake' instructions for implementing our optimal richness estimator, and we are releasing an implementation of the code that works with Sloan Digital Sky Survey data, as well as an augmented maxBCG catalog with the {lambda} richness measured for each cluster.
- OSTI ID:
- 22011656
- Journal Information:
- Astrophysical Journal, Vol. 746, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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