PLCK G165.7+67.0: Analysis of a Massive Lensing Cluster in a Hubble
  Space Telescope Census of Submillimeter Giant Arcs Selected Using
  Planck/Herschel
  We present Hubble Space Telescope WFC3-IR imaging in the fields of six
apparently bright dusty star-forming galaxies (DSFGs) at $z$ = 2-4 identified
by their rest-frame far-infrared colors using the Planck and Herschel space
facilities. We detect near-infrared counterparts for all six submillimeter
sources, allowing us to undertake strong-lensing analyses. One field in
particular stands out for its prominent giant arcs, PLCK G165.7+67.0 (G165).
After combining the color and morphological information, we identify 11 sets of
image multiplicities in this one field. We construct a strong-lensing model
constrained by this lensing evidence, which uncovers a bimodal spatial mass
distribution, and from which we measure a mass of $(2.6 \pm 0.11)$ $\times$
$10^{14}$ $M_{\odot}$ within $\sim$250 kpc. The bright ($S_{350}$ $\approx$ 750
mJy) DSFG appears as two images: a giant arc with a spatial extent of 4.5" that
is merging with the critical curve, and a lower-magnification counterimage that
is detected in our new longer-wavelength ground- and space-based imaging data.
Using our ground-based spectroscopy, we calculate a dynamical mass of
$1.3^{+0.04}_{-0.70} \times 10^{15}$ $M_{\odot}$ to the same fixed radius,
although this value may be inflated relative to the true value if the velocity
distribution is enhanced in the line-of-sight direction. We suggest that the
bimodal mass taken in combination with the weak X-ray flux and low SZ decrement
may be explained as a pre-merger for which the intracluster gas is diluted
along the line of sight, while the integrated surface mass density is
supercritical to strong-lensing effects.
