UNVEILING THE THREE-DIMENSIONAL STRUCTURE OF GALAXY CLUSTERS: RESOLVING THE DISCREPANCY BETWEEN X-RAY AND LENSING MASSES

We present the first determination of the intrinsic three-dimensional (3D) shapes and the physical parameters of both dark matter (DM) and intracluster medium (ICM) in a triaxial galaxy cluster. While most previous studies rely on the standard spherical modeling, our approach allows us to infer the properties of the non-spherical intracluster gas distribution sitting in hydrostatic equilibrium within triaxial DM halos by combining X-ray, weak-lensing, and strong-lensing observations. We present an application of our method to the galaxy cluster MACS J1423.8+2404. This source is an example of a well-relaxed object with a unimodal mass distribution, and we infer shape and physical properties of the ICM and the DM for this source. We found that this is a triaxial galaxy cluster with DM halo axial ratios 1.53 ± 0.15 and 1.44 ± 0.07 on the plane of the sky and along the line of sight, respectively. We show that accounting for the 3D geometry allows us to solve the long-standing discrepancy between galaxy cluster masses determined from X-ray and gravitational-lensing observations. We also focus on the determination of the inner slope of the DM density profile α, since the cuspiness of DM density profiles in the central regions is one of the critical tests of the cold dark matter (CDM) paradigm for structure formation: we measure α = 0.94 ± 0.09 by accounting explicitly for the 3D structure for this cluster, a value that is close to the CDM predictions, while the standard spherical modeling leads to the biased value α = 1.24 ± 0.07. Our study proves that it is not possible to disprove the manifestation of the DM with ∼0.25% of error in failing to reject the null hypothesis. Our findings provide further evidences that support the CDM scenario and open a new window in recovering the intrinsic shapes and desired physical parameters of galaxy clusters in a bias-free way. This has important consequences in using galaxy clusters as cosmological probes.

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