Lens Model and Source Reconstruction Reveal the Morphology and Star
  Formation Distribution in the Cool Spiral LIRG SGAS J143845.1$+$145407
  We present $Hubble\ Space\ Telescope$ ($HST$) imaging and grism spectroscopy
of a strongly lensed LIRG at $z=0.816$, SGAS 143845.1$+$145407, and use the
magnification boost of gravitational lensing to study the distribution of star
formation throughout this galaxy. Based on the $HST$ imaging data, we create a
lens model for this system; we compute the mass distribution and magnification
map of the $z=0.237$ foreground lens. We find that the magnification of the
lensed galaxy ranges between $2$ and $10$, with a total magnification (measured
over all the images of the source) of $\mu=11.8^{+4.6}_{-2.4}$. We find that
the total projected mass density within $\sim34$ kpc of the brightest cluster
galaxy is $6.0^{+0.3}_{-0.7}\times10^{12}\,M_{\odot}$. Using the lens model we
create a source reconstruction for SGAS 143845.1$+$145407, which paired with a
faint detection of H$\alpha$ in the grism spectroscopy, allows us to finally
comment directly on the distribution of star formation in a $z\sim1$ LIRG. We
find widespread star formation across this galaxy, in agreement with the
current understanding of these objects. However, we note a deficit of H$\alpha$
emission in the nucleus of SGAS 143845.1$+$145407, likely due to dust
extinction.
