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

Abstract

ABSTRACTWe present analysis of 63 nearby (<44 Mpc) early-type galaxies hosting nuclear star clusters using the recently discovered parameter central intensity ratio (CIRI) determined from near-infrared (3.6 $\mu$m) observations with the Infrared Array Camera of Spitzer Space Telescope. The CIRI, 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 CIRI 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.