Correlations between Central Massive Objects and Their Host Galaxies: From Bulgeless Spirals to Ellipticals

Recent observations by Ferrarese et al. (2006) and Wehner et al. (2006)reveal that a majority of galaxies contain a central massive object (CMO),either a supermassive black hole (SMBH) or a compact stellar nucleus,regardless of the galaxy mass or morphological type, and that there is a tightrelation between the masses of CMOs and those of the host galaxies. Severalrecent studies show that feedback from black holes can successfully explain the$\msigma$ correlation in massive elliptical galaxies that contain SMBHs.However, puzzles remain in spirals or dwarf spheroids that do not appear tohave black holes but instead harbor a compact central stellar cluster. Here weuse three-dimensional, smoothed particle hydrodynamics simulations of isolatedgalaxies to study the formation and evolution of CMOs in bulgeless diskgalaxies, and simulations of merging galaxies to study the transition of theCMO--host mass relation from late-type bulgeless spirals to early-typeellipticals. Our results suggest that the observed correlations may beestablished primarily by the depletion of gas in the central region byaccretion and star-formation, and may hold for all galaxy types. A systematicsearch for CMOs in the nuclei of bulgeless disk galaxies would offer a test ofthis conclusion. (Abridged)Comment: 11 pages, 8 figures, accepted to Ap