Robust Optical Richness Estimation with Reduced Scatter

Journal Article · Thu Jun 07 00:00:00 EDT 2012 · Astrophys.J.746:178,2012

DOI:https://doi.org/10.1088/0004-637X/746/2/178· OSTI ID:1042662

Rykoff, E S; Koester, B P; Rozo, E; Annis, J; Evrard, A E; Hansen, S M; Hao, J; Johnston, D E; McKay, T A; Wechsler, R H

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. (2009b), and evaluate their impact on the scatter in X-ray luminosity at fixed richness. Most significantly, we find that deeper luminosity cuts can reduce the recovered scatter, finding that {sigma}{sub ln L{sub X}|{lambda}} = 0.63 {+-} 0.02 for clusters with M{sub 500c} {approx}> 1.6 x 10{sup 14} h{sub 70}{sup -1} M{sub {circle_dot}}. The corresponding scatter in mass at fixed richness is {sigma}{sub ln M|{lambda}} {approx} 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 {angstrom} 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 SDSS data, as well as an augmented maxBCG catalog with the {lambda} richness measured for each cluster.

• Research Organization: SLAC National Accelerator Laboratory (SLAC)
• Sponsoring Organization: US DOE Office of Science (DOE SC)
• DOE Contract Number: AC02-76SF00515
• OSTI ID: 1042662
• Report Number(s): SLAC-PUB-15068; arXiv:1104.2089
• Journal Information: Astrophys.J.746:178,2012, Journal Name: Astrophys.J.746:178,2012 Journal Issue: 2 Vol. 746; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
79 ASTRONOMY AND ASTROPHYSICS
Astrophysics
ASTRO
COSMOLOGY
GALAXIES
IMPLEMENTATION
LUMINOSITY
MODIFICATIONS