CHEX-MATE: Are we getting cluster thermodynamics right?

Abstract

Galaxy clusters offer powerful insights into the large-scale structure of the Universe and the physics of baryons in hot state. Their scientific exploitation, however, hinges on our ability to accurately measure key thermodynamic properties. In this work, we aim to assess the reliability of current analysis techniques in reconstructing these properties, with particular focus on samples similar to those observed in the Cluster HEritage project with XMM-Newton (CHEX-MATE). We develop a suite of dedicated end-to-end simulations of CHEX-MATE-like clusters selected from large scale hydrodynamical simulations, and processed through a newly developed realistic XMM-Newton simulator. We apply a full X-ray data analysis pipeline to the mock datasets, including imaging, spectral fitting, and profile reconstruction. The gas density profiles can be robustly recovered across a wide radial range, when using azimuthal mean surface brightness profiles. Our reconstruction techniques are able to reproduce the intrinsic density profile with the correct scatter, with deviations of at most 10% between 0.1 and 1xR500c. The gas mass is reconstructed with better than 1% accuracy. Accurate measurement of temperature profiles is more challenging and possibly subject to biases, particularly in the presence of azimuthal variations and multi-temperature gas along the line of sight, which dominate over projection effects. Our results highlight the need for caution in interpreting cluster temperature measurements and underscore the value of tailored mock observations for understanding observational systematics. These findings also suggest that biases in X-ray temperature measurements may alter the interpretation of the thermodynamical state of the intra-cluster medium, an outlook particularly relevant in light of recent low velocity measurements from the XRISM mission.

Figures (21)

• Figure 1: Mass and redshift distribution of the CHEX-MATE clusters compared to the twin selected systems from The300, Magneticum, and MACSIS. The CHEX-MATE masses include the hydrostatic mass bias of 0.2.
• Figure 2: Example of a simulated XMM-Newton EPIC image for one cluster. The black lines denote the regions used for spectral extraction to measure its temperature profile. The red circle denotes R$_{\rm 500c}$.
• Figure 3: Gas density profiles in our simulations. Top panel: comparison between the measured (solid lines and shaded areas) and true (dashed lines) gas density profiles in different simulations (in various colours), using the NFW reconstruction. Bottom panel: intrinsic scatter as a function of radius.
• Figure 4: Ratio between the result of the X-ray spectral fitting and the input spectroscopic-like temperature profile. The profiles are also split between cool core (CC) and non cool core (NCC) according to the median surface brightness concentration reported as text in the panel.
• Figure 5: Gas temperature profiles. Each panel corresponds to one simulation: The300 on the left, Magneticum in the centre, and MACSIS on the right. The colours denote the three reconstruction methods. The smaller panels show the ratio between the reconstructed 2D and deprojected 3D profiles.