Linking a universal gas density profile to the core-excised X-ray luminosity in galaxy clusters up to z ∼ 1.1

Abstract

We investigate the regularity of galaxy cluster gas density profiles and the link to the relation between core-excised luminosity, LXc, and mass from the YX proxy, MYX, for 93 objects selected through their Sunyaev-Zeldovich effect (SZE) signal. The sample spans a mass range of M500 = [0.5−20]×1014 M⊙, and lies at redshifts 0.05 < z < 1.13. To investigate differences in X-ray and SZE selection, we compare to the local X-ray-selected REXCESS sample. Using XMM-Newton observations, we derive an average intra-cluster medium (ICM) density profile for the SZE-selected systems and determine its scaling with mass and redshift. This average profile exhibits an evolution that is slightly stronger than self-similar (αz = 2.09 ± 0.02), and a significant dependence on mass (αM = 0.22 ± 0.01). Deviations from this average scaling with radius, which we quantify, indicate different evolution for the core regions as compared to the bulk. We measure the radial variation of the intrinsic scatter in scaled density profiles, finding a minimum of ∼20% at R ∼ [0.5−0.7] R500 and a value of ∼40% at R500; moreover, the scatter evolves slightly with redshift. The average profile of the SZE-selected systems adequately describes the X-ray-selected systems and their intrinsic scatter at low redshift, except in the very central regions. We examine the evolution of the scaled core properties over time, which are positively skewed at later times, suggesting an increased incidence of centrally peaked objects at lower redshifts. The relation between core-excised luminosity, LXc, and mass is extremely tight, with a measured logarithmic intrinsic scatter of σlnLXc|MYx ∼ 0.13. Using extensive simulations, we investigate the impact of selection effects, intrinsic scatter, and covariance between quantities on this relation. The slope is insensitive to selection and intrinsic scatter between quantities; however, the scatter is very dependent on the covariance between LXc and YX. Accounting for our use of the YX proxy to determine the mass, for observationally motivated values of covariance we estimate an upper limit to the logarithmic intrinsic scatter with respect to the true mass of σlnLXc|M ∼ 0.22. We explicitly illustrate the connection between the scatter in density profiles and that in the LXc − M relation. Our results are consistent with the overall conclusion that the ICM bulk evolves approximately self-similarly, with the core regions evolving separately. They indicate a systematic variation of the gas content with mass. They also suggest that the core-excised X-ray luminosity, LXc, has a tight and well-understood relation to the underlying mass.