Finding the One: Identifying the Host Galaxies of Gravitational-Wave
  Sources
  We explore the localization of compact binary coalescences with ground-based
gravitational-wave detector networks. We simulate tens of thousands of binary
events, and present the distributions of localization sky areas and
localization volumes for a range of sources and network configurations. We show
that generically there exists a tail of particularly well-localized events,
with 2D and 3D localizations of $<10\,\mbox{deg}^2$ and $<1000\,\mbox{Mpc}^3$
achievable, respectively, starting in LIGO/Virgo's third observing run.
Incorporating estimates for the galaxy density and the binary event rates, we
argue that future gravitational-wave detector networks will localize a small
number of binary systems per year to a sufficiently small volume that the
unique host galaxy might be identified. For these golden events, which are
generally the closest and loudest ones, the gravitational-wave detector
networks will point (in 3D; the length of the finger matters) directly at the
source. This will allow for studies of the properties of the host galaxies of
compact binary mergers, which may be an important component in exploring the
formation channels of these sources. In addition, since the host will provide
an independent measurement of the redshift, this will allow the use of the
event as a standard siren to measure cosmology. Furthermore, identification of
a small number of host galaxies can enable deep follow-up searches for
associated electromagnetic transients.
