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 roughly50-80% of low- and intermediate-luminosity galaxies contain a compact stellarnucleus at their center, regardless of host galaxy morphological type. Wecombine HST imaging for early-type galaxies from the ACS Virgo Cluster Surveywith ground-based long-slit spectra from KPNO to show that the masses ofcompact stellar nuclei in Virgo Cluster galaxies obey a tight correlation withthe masses of the host galaxies. The same correlation is obeyed by thesupermassive black holes (SBHs) found in predominantly massive galaxies. Thecompact stellar nuclei in the Local Group galaxies M33 and NGC205 are alsofound to fall along this same scaling relation. These results indicate that ageneric by-product of galaxy formation is the creation of a Central MassiveObject (CMO) -- either a SBH or a compact stellar nucleus -- that contains amean fraction, ~ 0.2%, of the total galactic mass. In galaxies with massesgreater than a few times 10^10 solar masses, SBHs appear to be the dominantmode of CMO formation.