CLASH-VLT: Dissecting the Frontier Fields Galaxy Cluster MACS
  J0416.1-2403 with $\sim800$ Spectra of Member Galaxies
  We present VIMOS-VLT spectroscopy of the Frontier Fields cluster
MACS~J0416.1-2403 (z=0.397). Taken as part of the CLASH-VLT survey, the large
spectroscopic campaign provided more than 4000 reliable redshifts, including
~800 cluster member galaxies. The unprecedented sample of cluster members at
this redshift allows us to perform a highly detailed dynamical and structural
analysis of the cluster out to ~2.2$r_{200}$ (~4Mpc). Our analysis of
substructures reveals a complex system composed of a main massive cluster
($M_{200}$~0.9$\times 10^{15} M_{\odot}$) presenting two major features: i) a
bimodal velocity distribution, showing two central peaks separated by $\Delta
V_{rf}$~1100 km s$^{-1}$ with comparable galaxy content and velocity
dispersion, ii) a projected elongation of the main substructures along the
NE-SW direction, with a prominent subclump ~600 kpc SW of the center and an
isolated BCG approximately halfway between the center and the SW clump. We also
detect a low mass structure at z~0.390, ~10' S of the cluster center, projected
at ~3Mpc, with a relative line-of-sight velocity of $\Delta V_{rf}$~-1700 km
s$^{-1}$. The cluster mass profile that we obtain through our dynamical
analysis deviates significantly from the "universal" NFW, being best fit by a
Softened Isothermal Sphere model instead. The mass profile measured from the
galaxy dynamics is found to be in relatively good agreement with those obtained
from strong and weak lensing, as well as with that from the X-rays, despite the
clearly unrelaxed nature of the cluster. Our results reveal overall a complex
dynamical state of this massive cluster and support the hypothesis that the two
main subclusters are being observed in a pre-collisional phase, in line with
recent findings from radio and deep X-ray data. With this article we also
release the entire redshift catalog of 4386 sources in the field of this
cluster.
