Missing Lensed Images and the Galaxy Disk Mass in CXOCY J220132.8-320144
  The CXOCY J220132.8-320144 system consists of an edge-on spiral galaxy
lensing a background quasar into two bright images. Previous efforts to
constrain the mass distribution in the galaxy have suggested that at least one
additional image must be present (Castander et al. 2006). These extra images
may be hidden behind the disk which features a prominent dust lane. We present
and analyze Hubble Space Telescope (HST) observations of the system. We do not
detect any extra images, but the observations further narrow the observable
parameters of the lens system. We explore a range of models to describe the
mass distribution in the system and find that a variety of acceptable model
fits exist. All plausible models require 2 magnitudes of dust extinction in
order to obscure extra images from detection, and some models may require an
offset between the center of the galaxy and the center of the dark matter halo
of 1 kiloparsec. Currently unobserved images will be detectable by future James
Webb Space Telescope (JWST) observations and will provide strict constraints on
the fraction of mass in the disk.
