Paper detail

The mass profile and dynamical status of the z~0.8 galaxy cluster LCDCS 0504

Constraints on the mass distribution in high-redshift clusters of galaxies are not currently very strong. We aim to constrain the mass profile, M(r), and dynamical status of the $z \sim 0.8$ LCDCS 0504 cluster of galaxies characterized by prominent giant gravitational arcs near its center. Our analysis is based on deep X-ray, optical, and infrared imaging, as well as optical spectroscopy. We model the mass distribution of the cluster with three different mass density profiles, whose parameters are constrained by the strong lensing features of the inner cluster region, by the X-ray emission from the intra-cluster medium, and by the kinematics of 71 cluster members. We obtain consistent M(r) determinations from three methods (dispersion-kurtosis, caustics and MAMPOSSt), out to the cluster virial radius and beyond. The mass profile inferred by the strong lensing analysis in the central cluster region is slightly above, but still consistent with, the kinematics estimate. On the other hand, the X-ray based M(r) is significantly below both the kinematics and strong lensing estimates. Theoretical predictions from $Λ$CDM cosmology for the concentration--mass relation are in agreement with our observational results, when taking into account the uncertainties in both the observational and theoretical estimates. There appears to be a central deficit in the intra-cluster gas mass fraction compared to nearby clusters. Despite the relaxed appearance of this cluster, the determinations of its mass profile by different probes show substantial discrepancies, the origin of which remains to be determined. The extension of a similar dynamical analysis to other clusters of the DAFT/FADA survey will allow to shed light on the possible systematics that affect the determination of mass profiles of high-z clusters, possibly related to our incomplete understanding of intracluster baryon physics.