Detecting Thin Stellar Streams in External Galaxies: Resolved Stars &
  Integrated Light
  The morphology of thin stellar streams can be used to test the nature of dark
matter. It is therefore crucial to extend searches for globular cluster streams
to other galaxies than the Milky Way. In this paper, we investigate the current
and future prospects of detecting globular cluster streams in external galaxies
in resolved stars (e.g. with WFIRST) and using integrated light (e.g. with HSC,
LSST and Euclid). In particular, we inject mock-streams to data from the PAndAS
M31 survey, and produce simulated M31 backgrounds mimicking what WFIRST will
observe in M31. Additionally, we estimate the distance limit to which globular
cluster streams will be observable. Our results demonstrate that for a 1 hour
(1000 sec.) exposure, using conservative estimates, WFIRST should detect
globular cluster streams in resolved stars in galaxies out to distances of ~3.5
Mpc (~2 Mpc). This volume contains 199 (122) galaxies of which >90% are dwarfs.
With integrated light, thin streams can be resolved out to ~100 Mpc with HSC
and LSST and to ~600 Mpc with WFIRST and Euclid. The low surface brightness of
the streams (typically >30 mag/arcsec$^2$), however, will make them difficult
to detect, unless the streams originate from very young clusters. We emphasize
that if the external galaxies do not host spiral arms or galactic bars, gaps in
their stellar streams provide an ideal test case for evidence of interactions
with dark matter subhalos. Furthermore, obtaining a large samples of thin
stellar streams can help constrain the orbital structure and hence the
potentials of external halos.
