Do Nuclear Star Clusters and Supermassive Black Holes Follow the Same Host-Galaxy Correlations?

Recent studies have suggested a strong correlation between the masses of nuclear star clusters and their host galaxies, an extension of the known correlations between supermassive black holes (SMBHs) and their host galaxies. By focusing on disk galaxies with well-determined black hole and nuclear cluster masses, we argue that there is not a universal "central massive object" correlation after all: careful analysis shows that while SMBHs correlate better with the stellar masses of the bulge components, nuclear star clusters clearly correlate better with total galaxy stellar mass.