Free-form Grale reconstruction of Abell 2744: robustness of
  uncertainties against changes in lensing data
  Abell 2744, a massive Hubble Frontier Fields merging galaxy cluster with many
multiple images in the core has been the subject of many lens inversions using
different methods. While most existing studies compare various inversion
methods, we focus on a comparison of reconstructions that use different input
lensing data. Since the quantity and quality of lensing data is constantly
improving, it makes sense to ask if the estimated uncertainties are robust
against changes in the data. We address this question using free-form Grale,
which takes only image information as input, and nothing pertaining to cluster
galaxies. We reconstruct Abell 2744 using two sets of strong lensing data from
the Hubble Frontier Fields community. Our first and second reconstructions use
55 and 91 images, respectively, and only 10 of the 91 images have the same
positions and redshifts as in the first reconstruction. Comparison of the two
mass maps shows that Grale uncertainties are robust against these changes, as
well as small modifications in the inversion routine. Additionally, applying
the methods used in Sebesta et al. (2016) for MACS J0416, we conclude that, in
a statistical sense, light follows mass in Abell 2744, with brighter galaxies
clustering stronger with the recovered mass than the fainter ones. We also show
that the faintest galaxies are anti-correlated with mass, which is likely the
result of light contamination from bright galaxies, and lensing magnification
bias acting on galaxies background to the cluster.
