  Using a combination of numerical simulation and synthesized Hubble Space
Telescope Wide Field Camera 2 (HST WFC2) images, we follow the detectability of
morphological signatures of disk galaxy mergers at intermediate redshifts z=0.4
and z=1.0. Rapid evolution in the surface brightness of tidal tails makes their
use as an interaction signature limited; long tidal tails will only be
detectable relatively early in the encounter, before the galaxies actually
merge. Violent relaxation rapidly smooths isophotal irregularities after the
galaxies merge, leaving the very low surface brightness tidal debris
surrounding the remnant as the only sign of peculiarity after a few hundred
Myr. This debris becomes indistinguishable from the main body of the remnant
after 0.5 (z=1.0) to 1 (z=0.4) Gyr, leaving a morphologically normal elliptical
galaxy behind. Using WFC1, all signatures become undetectable almost
immediately once the galaxies merge, due to the aberrated PSF. We interpret
these results in light of recent HST programs investigating the nature of
starburst and E+A galaxies in moderate redshift clusters.
