Deep imaging of the shell elliptical galaxy NGC3923 with MegaCam
  Context. The elliptical galaxy NGC 3923 is known to be surrounded by a number
of stellar shells, probable remnants of an accreted galaxy. Despite its
uniqueness, the deepest images of its outskirts come from the 1980s. On the
basis of the modified Newtonian dynamics (MOND), it has recently been predicted
that a new shell lies in this region.
  Aims. We obtain the deepest image ever of the galaxy, map the tidal features
in it, and search for the predicted shell.
  Methods. The image of the galaxy was taken by the MegaCam camera at the
Canada-France-Hawaii Telescope in the g' band. It reached the
surface-brightness limit of 29 mag/arcsec2. In addition, we reanalyzed an
archival HST image of the galaxy.
  Results. We detected up to 42 shells in NGC 3923. This is by far the highest
number among all shell galaxies. We present the description of the shells and
other tidal features in the galaxy. A probable progenitor of some of these
features was discovered. The shell system likely originates from two or more
progenitors. The predicted shell was not detected, but the new image revealed
that the prediction was based on incorrect assumptions and poor data.
