On the Discrepancy between Theoretical and X-Ray Concentration-Mass Relations for Galaxy Clusters

TL;DR

This study investigates the discrepancies between theoretical and X-ray derived concentration-mass relations for galaxy clusters, analyzing simulation and observational methods to identify factors influencing these differences.

Contribution

It systematically examines how analysis methods, baryonic physics, and selection effects impact the observed and simulated concentration-mass relations.

Findings

X-ray approach and selection functions significantly affect the relation.

Radial range and baryonic physics have minor effects.

Discrepancies can be alleviated by considering observational biases.

Abstract

[Abridged] In the past 15 years, the concentration-mass relation has been investigated diffusely in theoretical studies. On the other hand, only recently has this relation been derived from X-ray observations. When that happened, the results caused a certain level of concern: the X-ray normalizations and slopes were found significantly dissimilar from those predicted by theory. We analyzed 52 objects, simulated each time with different physical recipes for the baryonic component, as well as 60 synthetic X-ray images, to determine if these discrepancies are real or artificial. In particular, we investigate how the simulated concentration-mass relation depends (1) on the radial range used to derive the concentration, (2) on the presence of baryons in the simulations, and on the prescription used to reproduce the gas. Finally, we evaluate (3) how the results differ when adopting an X-ray approach for the analysis and (4) how the selection functions based on X-ray luminosity can impact the results. All effects studied go in the direction of alleviating the discrepancy between observations and simulations, although with different significance: while the fitting radial range and the baryonic component play only a minor role, the X-ray approach and selection function have profound repercussion on the resulting concentration-mass relation.