Testing light-traces-mass in Hubble Frontier Fields Cluster
  MACS-J0416.1-2403
  We reconstruct the projected mass distribution of a massive merging Hubble
Frontier Fields cluster MACSJ0416 using the genetic algorithm based free-form
technique called Grale. The reconstructions are constrained by 149 lensed
images identified by Jauzac et al. using HFF data. No information about cluster
galaxies or light is used, which makes our reconstruction unique in this
regard. Using visual inspection of the maps, as well as galaxy-mass correlation
functions we conclude that overall light does follow mass. Furthermore, the
fact that brighter galaxies are more strongly clustered with mass is an
important confirmation of the standard biasing scenario in galaxy clusters. On
the smallest scales, approximately less than a few arcseconds, the resolution
afforded by 149 images is still not sufficient to confirm or rule out
galaxy-mass offsets of the kind observed in ACO 3827. We also compare the mass
maps of MACSJ0416 obtained by three different groups: Grale, and two parametric
Lenstool reconstructions from the CATS and Sharon/Johnson teams. Overall, the
three agree well; one interesting discrepancy between Grale and Lenstool
galaxy-mass correlation functions occurs on scales of tens of kpc and may
suggest that cluster galaxies are more biased tracers of mass than parametric
methods generally assume.
