A Weak Lensing Study of X-ray Groups in the Cosmos Survey: Form and Evolution of the Mass-Luminosity Relation

Abstract

Measurements of X-ray scaling laws are critical for improving cosmological constraints derived with the halo mass function and for understanding the physical processes that govern the heating and cooling of the intracluster medium. In this paper, we use a sample of 206 X-ray-selected galaxy groups to investigate the scaling relation between X-ray luminosity (L_X) and halo mass (M_(200)) where M_(200) is derived via stacked weak gravitational lensing. This work draws upon a broad array of multi-wavelength COSMOS observations including 1.64 degrees^2 of contiguous imaging with the Advanced Camera for Surveys to a limiting magnitude of I_(F814W) = 26.5 and deep XMM-Newton/Chandra imaging to a limiting flux of 1.0 × 10^(–15) erg cm6(–2) s^(–1) in the 0.5-2 keV band. The combined depth of these two data sets allows us to probe the lensing signals of X-ray-detected structures at both higher redshifts and lower masses than previously explored. Weak lensing profiles and halo masses are derived for nine sub-samples, narrowly binned in luminosity and redshift. The COSMOS data alone are well fit by a power law, M_(200) (L_X)^α, with a slope of α = 0.66 ± 0.14. These results significantly extend the dynamic range for which the halo masses of X-ray-selected structures have been measured with weak gravitational lensing. As a result, tight constraints are obtained for the slope of the M-L_X relation. The combination of our group data with previously published cluster data demonstrates that the M-L_X relation is well described by a single power law, α = 0.64 ± 0.03, over two decades in mass, M_(200) ~ 10^(13.5)-10^(15.5) h^(–1)_72 M_☉. These results are inconsistent at the 3.7σ level with the self-similar prediction of α = 0.75. We examine the redshift dependence of the M-L_X relation and find little evidence for evolution beyond the rate predicted by self-similarity from z ~ 0.25 to z ~ 0.

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