The Frequency of Tidal Features Associated with Nearby Luminous
  Elliptical Galaxies from a Statistically Complete Sample
  We present a deep broadband optical imaging study of a complete sample of
luminous elliptical galaxies (M_B<-20) at distances 15 Mpc - 50 Mpc, selected
from the Tully catalog of nearby galaxies. The images are flat to ~0.35% across
the 20' field and reach a V band depth of 27.7 mag arcsec^-2. We derive an
objective tidal interaction parameter for all galaxies and find that 73% of
them show tidal disturbance signatures in their stellar bodies. This is the
first time that such an analysis is done on a statistically complete sample and
it confirms that tidal features in ellipticals are common even in the local
Universe. From the dynamical time of the sample galaxies at the innermost
radius where tidal features are detected we estimate the mass assembly rate of
nearby ellipticals to be dM/M 0.2 per Gyr with large uncertainty. We explore
the relation between gravitational interaction signatures and the galaxy
environment and find that galaxies in clusters are less disturbed than group
and field galaxies. We also study how these interactions affect the broadband
colors of ellipticals and find a moderate correlation, suggesting that the
mergers are not accompanied by significant star-formation. Lastly, we find no
correlation between AGN activity, as measured by 6cm radio emission, and large
scale tidal distortions. This implies that gravitational interactions are not
the only, and perhaps not the most important, trigger of nuclear activity. In
summary, we find that elliptical galaxies in groups and low density
environments continue to grow at the present day through mostly "dry" mergers
involving little star formation.
