Halo Retention and Evolution of Coalescing Compact Binaries in
  Cosmological Simulations of Structure Formation: Implications for Short
  Gamma-Ray Bursts
  Merging compact binaries are the one source of gravitational radiation so far
identified. Because short-period systems which will merge in less than a Hubble
time have already been observed as binary pulsars, they are important both as
gravitational wave sources for observatories such as LIGO but also as
progenitors for short gamma-ray bursts (SGRBs). The fact that these systems
must have large systemic velocities implies that by the time they merge, they
will be far from their formation site. The locations of merging sites depend
sensitively on the gravitational potential of the galaxy host, which until now
has been assumed to be static. Here we refine such calculations to incorporate
the temporal evolution of the host's gravitational potential as well as that of
its nearby neighbors using cosmological simulations of structure formation.
This results in merger site distributions that are more diffusively distributed
with respect to their putative hosts, with locations extending out to distances
of a few Mpc for lighter halos. The degree of mixing between neighboring
compact binary populations computed in this way is severely enhanced in
environments with a high number density of galaxies. We find that SGRB redshift
estimates based solely on the nearest galaxy in projection can be very
inaccurate, if progenitor systems inhere large systematic kicks at birth.
