On the fragility of nuclear stellar discs against galaxy mergers:
  surviving photometric and kinematic signatures of nuclear discs
  Nuclear stellar discs (NSDs) can help to constrain the assembly history of
their host galaxies, as long as we can assume them to be fragile structures
that are disrupted during merger events. In this work we investigate the
fragility of NSDs by means of N-body simulations reproducing the last phases of
a galaxy encounter, when the nuclear regions of the two galaxies merge. For
this, we exposed a NSD set in the gravitational potential of the bulge and
supermassive black hole of a primary galaxy to the impact of the supermassive
black hole from a secondary galaxy. We explored merger events of different mass
ratios, from major mergers with a 1:1 mass ratio to intermediate and minor
interactions with 1:5 and 1:10 ratios, while considering various impact
geometries. We analyse the end results of such mergers from different viewing
angles and looked for possible photometric and kinematic signatures of the
presence of a disc in the remnant surface density and velocity maps, while
adopting detection limits from real observations. Our simulations show that
indeed NSDs are fragile against major mergers, which leave little trace of NSDs
both in images and velocity maps, while signatures of a disc can be found in
the majority of the intermediate to minor-merger remnants and in particular
when looking at their kinematics. These results show that NSDs could allow to
distinguish between these two modes of galaxy assembly, which may indeed
pertain to different kinds of galaxies or galactic environments.
