# Study of central light distribution in nearby early-type galaxies hosting nuclear star clusters

## TL;DR

This study analyzes the central light distribution in nearby early-type galaxies with nuclear star clusters using the CIR$_I$ parameter, revealing distinct galaxy classes and correlations with galaxy properties and color.

## Contribution

Introduces the use of the Central Intensity Ratio (CIR$_I$) from Spitzer IR data to classify and analyze nuclear star clusters in early-type galaxies, identifying two galaxy classes and their properties.

## Key findings

- CIR$_I$ correlates with galaxy mass and color, indicating different nuclear star cluster characteristics.
- Redder galaxies tend to be black-hole dominated, while bluer galaxies are more likely to host nuclear star clusters.
- Distinct trends in nuclear star cluster properties are observed between low-mass, blue and high-mass, red galaxies.

## Abstract

We present analysis of 63 nearby ($<$ 44 Mpc) early-type galaxies hosting nuclear star clusters using the recently discovered parameter Central Intensity Ratio (CIR$_I$) determined from near-infra-red (3.6 $\mu$m) observations with the Infra-red-array-camera of \emph{Spitzer} space telescope. The CIR$_I$, when combined with filters involving age and $B-K$ colour of host galaxies, helps identify two distinct classes of galaxies hosting nuclear star clusters. This is independently verified using Gaussian Mixture Model. CIR shows a positive trend with faint, low mass, and blue galaxies in the sample, while the opposite is true for bright, high mass, and red galaxies, albeit with large scatter. The variation of CIR$_I$ with central velocity dispersion, absolute B band magnitude, dynamical mass, and stellar mass of host galaxies suggests that the mass of nuclear star clusters increases with that of host galaxies, for faint, low mass, young and blue galaxies in the sample. In bright, high-mass, old and red galaxies, on the other hand, the evolution of nuclear star clusters appears complex, with no apparent trends.The analysis also reveals that redder galaxies ($B-K > 3.76$) are more likely to be dominated by the central black-hole than the nuclear star clusters, while for bluer galaxies ($B-K < 3.76$) in the sample the situation is quite opposite.