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 (Lx) and halo mass (M00) where M200 is derived via stacked weak gravitational lensing. This work draws upon a broad array of multi-wavelength COSMOS observations including 1.64 square degrees of contiguous imaging with the Advanced Camera for Surveys (ACS) and deep XMM-Newton/Chandra imaging. 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, M200 ~ Lx^a, with a slope of a=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-Lx relation. The combination of our group data with previously published cluster data demonstrates that the M-Lx relation is well described by a single power law, a=0.64+-0.03, over two decades in mass, 10^13.5-10^15.5 h72^-1 Msun. These results are inconsistent at the 3.7 level with the self-similar prediction of a=0.75. We examine the redshift dependence of the M-Lx relation and find little evidence for evolution beyond the rate predicted by self-similarity from z ~ 0.25 to z ~ 0.8.

• The paper establishes a robust scaling relation between X-ray luminosity and halo mass using weak lensing data.
• It employs advanced halo modeling and weak lensing profiles from 206 groups to quantify a slope of β ≈ 0.64.
• The results challenge self-similar predictions and support improved calibration for cosmological mass-observable relations.

A Weak Lensing Analysis of X-Ray Groups in the COSMOS Survey

The study of galaxy groups via X-ray emissions is pivotal for understanding the complex interaction between baryonic matter and dark matter within cluster dynamics. The paper "A Weak Lensing Study of X-ray Groups in the COSMOS Survey: Form and Evolution of the Mass-Luminosity Relation" investigates the scaling relation between X-ray luminosity (L_X) and halo mass (M_200) determined through weak gravitational lensing. Utilizing a sample of 206 X-ray selected galaxy groups from the COSMOS survey, the study extends the range over which halo masses of X-ray detected structures have been measured, providing detailed constraints on the slope of the mass-luminosity relation.

Data and Methodology

This work relies on the comprehensive COSMOS dataset, which includes contiguous Advanced Camera for Surveys (ACS) imaging and deep XMM-Newton/Chandra observations. Halo masses are estimated through weak lensing profiles computed for nine sub-samples categorized by luminosity and redshift. These estimations are subject to an overarching mass-concentration relation derived for a WMAP5 cosmology.

The research applies a halo model approach to model the signal at varying scales, considering contributions from the central galaxy and the dark matter halo. Additionally, the study emphasizes the importance of correcting for systematic biases such as mis-centering errors and photometric redshift inaccuracies.

Results

The COSMOS data reveal that the observed power-law relation between M_200 and (L_X ∙ E(z)^-1) is well fitted, yielding a slope of β = 0.66 ± 0.14 when COSMOS data are considered independently. Notably, the slope observed in the research is in tension with the self-similar prediction of β = 0.75 at a 3.7σ level.

By combining COSMOS results with published cluster data, the slope is refined to β = 0.64 ± 0.03. This refined result — tracing a continuous scale up from groups to clusters — indicates no significant break in the mass-luminosity relation beyond the intrinsic scatter already accounted for.

Evolution and Theoretical Implications

When examining redshift dependence, the results suggest limited evidence for evolution in the M-L_X relation beyond the predictions of self-similar models from redshift z ≈ 0.25 to z ≈ 0.8. This observation supports hypotheses invoking other non-gravitational processes affecting the intra-cluster medium (ICM), which deviate from simple gravitational collapse scenarios.

Theoretical implications of the research stretch into cosmology, as the derived scaling relations are fundamental in constraining cosmological parameters and understanding the dark matter-dominated structure universe. The trivial disagreements in predicted and observed slopes suggest further examination into the complexities influencing X-ray scaling laws, such as feedback processes and equilibrium assumptions in gas dynamics.

Comparison and Conclusions

Comparison with other studies indicates a rough alignment of slopes around β ≈ 0.64 among lensing-based analyses and X-ray results, suggesting a robust scaling relation format across mass and redshift scales. Nonetheless, variations in specific data points, particularly the mass normalization, reflect the necessity for ongoing recalibration and convergence between distinct measurement methodologies.

The study provides critical insights into the calibration of observational mass-luminosity scalings necessary for utilizing galaxy clusters as cosmological probes, laying groundwork for future surveys and analyses expanding into high-redshift territories. Such developments are anticipated to enhance understanding of the mass-observable relations, essential for advancing self-calibration techniques in large-scale cosmological studies.