Weak-lensing mass distributions for 24 X-ray Abell clusters

Abstract

We use the weak gravitational lensing effect to study the mass distribution and dynamical state of a sample of 24 X-ray-luminous clusters of galaxies (0.05 < z < 0.31) observed with the FORS1 instrument mounted on the VLT-Antu (Unit Telescope 1) under homogeneous sky conditions and subarcsecond image quality. The galaxy shapes were measured in the combined VIR image after deconvolution with a locally determined point-spread function, while the two-dimensional mass distributions of the clusters were computed using an algorithm based on the maximum entropy method. By comparing the mass and light distributions of the clusters in our sample, we find that their centers of mass, for the majority of the clusters, are consistent with the positions of optical centers. We find that some clusters present significant mass substructures that generally have optical counterparts. In at least one cluster (A1451), we detect a mass substructure without an obvious luminous counterpart. The radial profile of the shear of the clusters was fitted using circular and elliptical isothermal distributions, which allowed the finding of a strong correlation between the orientation of the major axis of the matter distribution and the corresponding major axes of the brightest cluster galaxy light profiles. Estimates of how close to dynamical relaxation are these clusters were obtained through comparison of our weak-lensing mass measurements with the X-ray and velocity dispersion determinations available in the literature. We find that clusters with intracluster gas colder than 8 keV show good agreement between the different mass determinations, but clusters with gas hotter than 8 keV present weak-lensing masses smaller than those inferred by the other methods and therefore have been diagnosed to be out of equilibrium. These clusters are A1451, A2163, and A2744, all of which have hints of substructure. A2744 presents the largest discrepancy between its X-ray, velocity dispersion, and weak-lensing mass determinations, which can be interpreted as being due to the interaction between the two kinematic components along the line of sight found by Girardi Mezzeti.