The Lx-Yx relation:: Using galaxy cluster X-ray luminosity as a robust, low-scatter mass proxy

We use a sample of 115 galaxy clusters at 0.1 < z < 1.3 observed with Chandra ACIS-I to investigate the relation between luminosity and Y-X (the product of gas mass and temperature). The scatter in the relation is dominated by cluster cores, and a tight L-X-Y-X relation (11% intrinsic scatter in L-X) is recovered if sufficiently large core regions (0.15R(500)) are excluded. The intrinsic scatter is well described by a lognormal distribution, and the relations are consistent for relaxed and disturbed/merging clusters. We investigate the L-X-Y-X relation in low-quality data (e. g., for clusters detected in X-ray survey data) by estimating L-X from soft-band count rates, and find that the scatter increases somewhat to 21%. We confirm the tight correlation between Y-X and mass and the self-similar evolution of that scaling relation out to z = 0.6 for a subset of clusters in our sample with mass estimates from the literature. This is used to estimate masses for the entire sample and hence measure the L-X-M relation. We find that the scatter in the L-X-M relation is much lower than previous estimates, due to the full removal of cluster cores and more robust mass estimates. For high-redshift clusters the scatter in the L-X-M relation remains low if cluster cores are not excluded. These results suggest that cluster masses can be reliably estimated from simple luminosity measurements in low-quality data where direct mass estimates, or measurements of Y-X, are not possible. This has important applications in the estimation of cosmological parameters from X-ray cluster surveys.