Supermassive black holes: Their masses, host galaxy relationships, and cosmic distribution

An investigation of four fundamental issues related to the ubiquitous supermassive black holes (SMBHs), found in the centers of all bulge-galaxies, is presented. (1) Using physically-different probes (stellar dynamical and water maser kinematical measurements), consistent SMBH masses are found for the test galaxy NGC 4258. (2) It was examined whether the SMBH mass is best-predicted by a single host galaxy property or by a combination of host galaxy properties (a multivariate predictor). (3) A related question of whether there exists a previously-unidentified, physical, host galaxy property which is at least as good as, or better than, established predictors of SMBH mass was also addressed. This investigation used a sample of 23 galaxies with both SMBH masses and host galaxy data taken from the literature. For the (15) elliptical galaxies in the sample, the answer to both host-galaxy-property-predictor questions is found to be a new predictor: the gravitational binding energy, as traced by the stellar light profile, M• ∝ E0.6g . For the (8) spiral/lenticular galaxies in the sample, the bulge gravitational binding energy is a good predictor, but the bulge mass may be a better predictor; spiral/lenticular galaxy bulges may not be as similar to elliptical galaxies as is often assumed in the literature and in models of SMBH-host galaxy evolution. Finally, (4) using a combination of galaxy luminosity functions and the M•(sigma) relationship, the cosmic mass density and mass distribution of SMBHs in the local universe is calculated. The cosmic mass density is found to be (4.8 +/- 1.6)h2 x 105 M⊙ Mpc-3, with the contribution from lenticular galaxies dominating the total mass density at low SMBH masses, and the contribution from elliptical galaxies dominating at high SMBH masses.