A Fundamental Relation between Compact Stellar Nuclei, Supermassive Black Holes, and Their Host Galaxies

Imaging surveys with the Hubble Space Telescope (HST) have shown that ≈50%-80% of low- and intermediate-luminosity galaxies contain a compact stellar nucleus at their center, regardless of host galaxy morphological type. We combine HST imaging for early-type galaxies from the ACS Virgo Cluster Survey with ground-based long-slit spectra from KPNO to show that the masses of compact stellar nuclei in Virgo Cluster galaxies obey a tight correlation with the masses of the host galaxies. The same correlation is obeyed by the supermassive black holes (SBHs) found in predominantly massive galaxies. The compact stellar nuclei in the Local Group galaxies M33 and NGC 205 are also found to fall along this same scaling relation. These results indicate that a generic by-product of galaxy formation is the creation of a central massive object (CMO)—either an SBH or a compact stellar nucleus—that contains a mean fraction, ≈0.2%, of the total galactic mass. In galaxies with masses greater than ℳgal ~ a few × 1010 ℳ☉, SBHs appear to be the dominant mode of CMO formation.