CLASH-VLT: Dissecting the Frontier Fields Galaxy Cluster MACS J0416.1-2403 with ˜800 Spectra of Member Galaxies

We present VIMOS-Very Large Telescope (VLT) spectroscopy of the FrontierFields cluster MACS J0416.1-2403 (z = 0.397). Taken as part of theCLASH-VLT survey the large spectroscopic campaign provided more than4000 reliable redshifts over ˜600 arcmin^2 including˜800 cluster member galaxies. The unprecedented sample of clustermembers at this redshift allows us to perform a highly detaileddynamical and structural analysis of the cluster out to ˜2.2 r_200 (˜4 Mpc). Our analysis of substructures reveals acomplex system composed of a main massive cluster (M _200˜ 0.9 × 10^15 M _⊙ and σ _Vr200 ˜ 1000 km s^-1) presenting two majorfeatures: (i) a bimodal velocity distribution showing two central peaksseparated by ΔV _rf ˜ 1100 km s^-1with comparable galaxy content and velocity dispersion and (ii) aprojected elongation of the main substructures along the NE-SWdirection with a prominent sub-clump ˜600 kpc SW of the centerand an isolated BCG approximately halfway between the center and the SWclump. We also detect a low-mass structure at z ˜ 0.390˜10‧ south of the cluster center projected at ˜3 Mpcwith a relative line-of-sight velocity of ΔV _rf ˜-1700 km s^-1. The cluster mass profile that weobtain through our dynamical analysis deviates significantly from the“universal” NFW being best fit by a Softened IsothermalSphere model instead. The mass profile measured from the galaxy dynamicsis found to be in relatively good agreement with those obtained fromstrong and weak lensing as well as with that from the X-rays despitethe clearly unrelaxed nature of the cluster. Our results reveal anoverall complex dynamical state of this massive cluster and support thehypothesis that the two main subclusters are being observed in apre-collisional phase in agreement with recent findings from radio anddeep X-ray data. In this article we also release the entire redshiftcatalog of 4386 sources in the field of this cluster which includes 60identified Chandra X-ray sources and 105 JVLA radio sources