Inside a Beehive: the Multiple Merging Processes in the Galaxy Cluster
  Abell 2142
  To investigate the dynamics of the galaxy cluster A2142, we compile an
extended catalog of 2239 spectroscopic redshifts of sources, including newly
measured 237 redshifts, within 30 arcmin from the cluster center. With the
$\sigma$-plateau algorithm from the caustic method, we identify 868 members and
a number of substructures in the galaxy distribution both in the outskirts, out
to $\sim$3.5 Mpc from the cluster center, and in the central region. In the
outskirts, one substructure overlaps a falling clump of gas previously
identified in the X-ray band. These substructures suggests the presence of
multiple minor mergers, which are responsible for the complex dynamics of
A2142, and the absence of recent or ongoing major mergers. We show that the
distribution of the galaxies in the cluster core and in several substructures
are consistent with the mass distribution inferred from the weak lensing
signal. Moreover, we use spatially-resolved X-ray spectroscopy to measure the
redshift of different regions of the intracluster medium within $\sim$3 arcmin
from the cluster center. We find a ring of gas near the two X-ray cold fronts
identified in previous analyses and measure a velocity of this ring of $810 \pm
330 {\rm km s^{-1}}$ larger than the cluster mean velocity. Our analysis
suggests the presence of another ring surrounding the core, whose velocity is
$660 \pm 300 {\rm km s^{-1}}$ larger than the cluster velocity. These X-ray
features are not associated to any optical substructures, and support the
core-sloshing scenario suggested in previous work.
