Dark matter distribution in the merging cluster Abell 2163

Context. The cluster Abell 2163 is a merging system of several subclusters with complex dynamics. It presents exceptional X-rays properties (high temperature and luminosity), suggesting that it is a very massive cluster. Recent 2D analysis of the gas distribution has revealed a complex and multiphase structure. Aims. This paper presents a wide-field weak lensing study of the dark matter distribution in the cluster in order to provide an alternative vision of the merging status of the cluster. The 2D mass distribution was built and compared to the galaxies and gas distributions. Methods. A Bayesian method, implemented in the IM2SHAPE software, was used to fit the shape parameters of the faint background galaxies and to correct for PSF smearing. A careful color selection on the background galaxies was applied to retrieve the weak lensing signal. Shear signal was measured out to more than 2 Mpc (similar or equal to 12' from the center). The radial shear profile was fit with different parametric mass profiles. The 2D mass map was built from the shear distribution and used to identify the different mass components. Results. The 2D mass map agrees with the galaxy distribution, while the total mass inferred from weak lensing shows a strong discrepancy to the X-ray deduced mass. Regardless of the method used, the virial mass M-200 falls in the range 8 to 14 x 10(14) h(70)(-1) M-circle dot inside the virial radius (similar to 2.0 h(70)(-1) Mpc), a value that is two times less than the mass deduced from X-rays. The central mass clump appears bimodal in the dark matter distribution, with a mass ratio similar to 3:1 between the two components. The infalling clump A2163-B is detected in weak lensing as an independent entity. All these results are interpreted in the context of a multiple merger seen less than 1 Gyr after the main crossover.