Testing MOND gravity in the shell galaxy NGC 3923
  Context. The elliptical galaxy NGC 3923 is surrounded by numerous stellar
shells that are concentric arcs centered on the galactic core. They are very
likely a result of a minor merger and they consist of stars in nearly radial
orbits. For a given potential, the shell radii at a given time after the merger
can be calculated and compared to observations. The Modified Newtonian Dynamics
(MOND) is a theory that aims to solve the missing mass problem by modifying the
laws of classical dynamics in the limit of small accelerations. Hernquist &
Quinn(1987) claimed that the shell distribution of NGC 3923 contradicted MOND,
but Milgrom(1988) found several substantial insufficiencies in their work.
  Aims. We test whether the observed shell distribution in NGC 3923 is
consistent with MOND using the current observational knowledge of the shell
number and positions and of the host galaxy surface brightness profile, which
supersede the data available in the 1980s when the last (and negative) tests of
MOND viability were performed on NGC 3923.
  Methods. Using the 3.6 um bandpass image of NGC 3923 from the Spitzer space
telescope we construct the mass profile of the galaxy. The evolution of shell
radii in MOND is then computed using analytical formulae. We use 27 currently
observed shells and allow for their multi-generation formation, unlike the
Hernquist & Quinn one-generation model that used the 18 shells known at the
time.
  Results. Our model reproduces the observed shell radii with a maximum
deviation of 5% for 25 out of 27 known shells while keeping a reasonable
formation scenario. A multi-generation nature of the shell system, resulting
from successive passages of the surviving core of the tidally disrupted dwarf
galaxy, is one of key ingredients of our scenario supported by the extreme
shell radial range. The 25 reproduced shells are interpreted as belonging to
three generations.
