| Abstract : | Nuclear star clusters are known to be the densest stellar systems in the universe with millions of solar masses packed within the central few parsecs of a galaxy and therefore host unique stellar dynamics. Studying how NSCs form and how they are related to the growth of central massive black holes and their host galaxies is crucial for our understanding of the evolution of galaxies and the physics that have shaped their central components. We present the analysis of 63 nearby ($<$ 44 Mpc) early-type galaxies hosting nuclear star clusters using the newly discovered parameter Central Intensity Ratio (CIR$_I$) obtained from near-infra-red (3.6 $\mu$m) observations with the Infra-red-array-camera of the Spitzer space telescope. Combining the CIR$_I$ with filters such as age and B-K colour helps identify two distinct classes of galaxies hosting nuclear star clusters. With faint, low-mass, blue galaxies in the sample, CIR$_I$ shows a positive trend, while bright, high-mass, red galaxies show the opposite trend, although with large scatters. The CIR$_I$ distribution varies with central velocity dispersion, the absolute magnitude of the B band, dynamical mass, and stellar mass of the host galaxies, indicating that the mass of the nuclear star clusters increases with the mass of the host galaxies, for faint, low mass, young, and blue galaxies. Nuclear star clusters appear to evolve complexly in galaxies with high mass, old, and red colours, where no trends seem to be evident. |
