The L_X--M relation of Clusters of Galaxies

TL;DR

This study measures the relationship between X-ray luminosity and total mass in a large sample of galaxy clusters, revealing a power-law scaling consistent with previous findings and discussing potential biases.

Contribution

It provides a new measurement of the L_X--M relation using stacking of optical and X-ray data for 17,000 clusters, with implications for understanding cluster properties and biases.

Findings

The L_X--M relation follows a power-law with a slope of 1.65.

The measured luminosity is 30% lower than previous X-ray flux-limited estimates.

The results suggest minimal covariance between optical richness and X-ray luminosity at fixed mass.

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 sub-samples 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 (Johnston et al. 2007). For 9 <= N_200 < 200, the data are well fit by a power-law, <L_X>/10^42 h^-2 erg/s = (12.6+1.4-1.3 (stat) +/- 1.6 (sys)) (<M_200>/10^14 h^-1 M_sun)^1.65+/-0.13. The slope agrees to within 10% with previous estimates based on X-ray selected catalogs, implying that the covariance in L_X and N_200 at fixed halo mass is not large. The luminosity intercent is 30%, or 2\sigma, lower than determined from the X-ray flux-limited sample of Reiprich & Bohringer (2002), assuming hydrostatic equilibrium. This 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. (2006) using a model for the statistical correspondence between clusters and halos in a WMAP3 cosmology with power spectrum normalization sigma_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 fixed mass.