Stellar populations and star formation histories of the nuclear star
  clusters in six nearby galaxies
  The majority of spiral and elliptical galaxies in the Universe host very
dense and compact stellar systems at their centres known as nuclear star
clusters (NSCs). In this work we study the stellar populations and star
formation histories (SFH) of the NSCs of six nearby galaxies with stellar
masses ranging between $2$ and $8\times10^9~{\rm M_{\odot}}$ (four late-type
spirals and two early-types) with high resolution spectroscopy. Our
observations are taken with the X-Shooter spectrograph at the VLT. We make use
of an empirical simple stellar population (SSP) model grid to fit composite
stellar populations to the data and recover the SFHs of the nuclei. We find
that the nuclei of all late-type galaxies experienced a prolonged SFH, while
the NSCs of the two early-types are consistent with SSPs. The NSCs in the
late-type galaxies sample appear to have formed a significant fraction of their
stellar mass already more than $10$ Gyr ago, while the NSCs in the two
early-type galaxies are surprisingly younger. Stars younger than $100$ Myr are
present in at least two nuclei: NGC 247 and NGC 7793, with some evidence for
young star formation in NGC 300's NSC. The NSCs of the spirals NGC 247 and NGC
300 are consistent with prolonged \in situ star formation with a gradual
metallicity enrichment from $\sim-1.5$ dex more than $10$ Gyr ago, reaching
super-Solar values few hundred Myr ago. NGC 3621 appears to be very metal rich
already in the early Universe and NGC 7793 presents us with a very complex SFH,
likely dominated by merging of various massive star clusters coming from
different environments.
