Exploring Effects on Magnifications due to Line-of-Sight Galaxies in the
  Hubble Frontier Fields
  Cluster lensing has become an important tool in the search for high redshift
galaxies through its ability to magnify sources. In order to determine the
intrinsic properties of these galaxies, lensing mass models must be constructed
to determine the magnification of the images. These models are traditionally
two-dimensional, focusing on the mass within the cluster and either ignoring or
approximating any contribution from line-of-sight galaxies. In this paper, we
present the first full set of three-dimensional mass models of the six Hubble
Frontier Fields and use them to test for systematic biases in magnifications
due to using the traditional 2D approach. We find that omitting foreground or
background galaxies causes image position offsets between 0.1-0.4", a
non-negligible fraction of the typical 0.3-0.7" residuals of current
state-of-the-art models. We also find that median image magnifications can
shift by up to 6%, though it is dependent on the field. This can be alleviated
in some cases by approximating the mass in the lensing plane, but a 5%
magnification bias still exists in other cases; image position offsets are also
improved, but are still present at 0.10".
