Dark matter distribution in the merging cluster Abell 2163
  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. 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 is built and
compared to the galaxies and gas distributions. 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 (~12' from the center). The
radial shear profile was fit with different parametric mass profiles. The 2D
mass map is built from the shear distribution and used to identify the
different mass components. 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 M200
falls in the range 8 to 14 10^14 Msol inside the virial radius (~ 2.0 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
~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 1Gyr after the main crossover.
