The L X – M relation of clusters of galaxies

Abstract

We present a new measurement of the scaling relation between X-ray luminosity and total mass for 17 000 galaxy clusters in the maxBCG cluster sample. Stacking subsamples within fixed ranges of optical richness, N 200 , we measure the mean 0.1–2.4 keV X-ray luminosity, 〈 L X 〉 , from the ROSAT All-Sky Survey. The mean mass, 〈 M 200 〉 , is measured from weak gravitational lensing of SDSS background galaxies. For 9 ≤ N 200 < 200 , the data are well fitted by a power law, 〈 L X 〉/10 42 h −2 erg s −1 =[12.6 +1.4 −1.3 (stat) ± 1.6 (sys)](〈 M 200 〉/10 14 h −1 M ) 1.65±0.13 . The slope agrees to within 10 per cent with previous estimates based on X-ray selected catalogues, implying that the covariance in L X and N 200 at a fixed halo mass is not large. The luminosity intercept is 30 per cent, or 2Σ, lower than that determined from the X-ray flux-limited sample of Reiprich & BÖhringer, assuming hydrostatic equilibrium. This slight difference could arise from a combination of Malmquist bias and/or systematic error in hydrostatic mass estimates, both of which are expected. The intercept agrees with that derived by Stanek et al. using a model for the statistical correspondence between clusters and haloes in a WMAP3 cosmology with power spectrum normalization Σ 8 = 0.85 . Similar exercises applied to future data sets will allow constraints on the covariance among optical and hot gas properties of clusters at a fixed mass.