Constraining nuclear star cluster formation using MUSE-AO observations
  of the early-type galaxy FCC47
  Nuclear star clusters (NSCs) are found in at least 70% of all galaxies, but
their formation path is still unclear. In the most common scenarios, NSCs form
in-situ from the galaxy's central gas reservoir, through merging of globular
clusters (GCs), or through a combination of the two. As the scenarios pose
different expectations for angular momentum and stellar population properties
of the NSC in comparison to the host galaxy and the GC system, it is necessary
to characterise the stellar light, NSC and GCs simultaneously. The large NSC
(r$_\rm{eff} = 66$ pc) and rich GC system of the early-type Fornax cluster
galaxy FCC47 (NGC1336) render this galaxy an ideal laboratory to constrain NSC
formation. Using MUSE science verification data assisted by adaptive optics, we
obtained maps for the stellar kinematics and for stellar-population properties
of FCC47. We extracted the spectra of the central NSC and determined
line-of-sight velocities of 24 GCs and metallicities of five. FCC47 shows two
decoupled components (KDCs): a rotating disk and the NSC. Our orbit-based
dynamical Schwarzschild model revealed that the NSC is a distinct kinematic
feature and it constitutes the peak of metallicity and old ages in the galaxy.
The main body consists of two counter-rotating populations and is dominated by
a more metal-poor population. The GC system is bimodal with a dominant
metal-poor population and the total GC system mass is $\sim 17\%$ of the NSC
mass ($\sim$ 7 $\times$ $10^8 M_\odot$). The rotation, high metallicity and
high mass of the NSC cannot be uniquely explained by GC-inspiral and most
likely requires additional, but quickly quenched, in-situ formation. The
presence of two KDCs most probably are evidence of a major merger that has
altered the structure of FCC47 significantly, indicating the important role of
galaxy mergers in forming the complex kinematics in the galaxy-NSC system.
