Searching for nuclear stellar discs in simulations of star cluster
  mergers
  The nuclei of galaxies often host small stellar discs with scale-lengths of a
few tens of parsecs and luminosities up to 10^7 Lsun. To investigate the
formation and properties of nuclear stellar discs (NSDs), we look for their
presence in a set of N-body simulations studying the dissipationless merging of
multiple star clusters in galactic nuclei. A few tens of star clusters with
sizes and masses comparable to those of globular clusters observed in the Milky
Way are accreted onto a pre-existing nuclear stellar component: either a
massive super star cluster or a rapidly rotating, compact disc with a
scale-length of a few parsecs, mimicing the variety of observed nuclear
structures. Images and kinematic maps of the simulation time-steps are then
built and analysed as if they were real and at the distance of the Virgo
cluster. We use the Scorza-Bender method to search for the presence of disc
structures via photometric decomposition. In one case the merger remnant has
all the observed photometric and kinematic properties of NSDs observed in real
galaxies. This shows that current observations are consistent with most of the
NSD mass being assembled from the migration and accretion of star clusters into
the galactic centre. In the other simulation instead, we detect an elongated
structure from the unsharp masked image, that does not develop the photometric
or kinematic signature of a NSD. Thus, in the context of searches for a disc
structure, the Scorza-Bender method is a robust and necessary tool.
