The influence of dark matter halos on dynamical estimates of black hole mass: 10 new measurements for high-σ early-type galaxies

Adaptive optics assisted SINFONI observations of the central regions of 10 early-type galaxies are presented. Based primarily on the SINFONI kinematics, 10 black hole (BH) masses occupying the high-mass regime of the M _⊙BH-σ relation are derived using three-integral Schwarzschild models. The effect of dark matter (DM) inclusion on the BH mass is explored. The omission of a DM halo in the model results in a higher stellar mass-to-light ratio, especially when extensive kinematic data are used in the model. However, when the diameter of the sphere of influence - computed using the BH mass derived without a dark halo - is at least 10 times the point-spread function FWHM during the observations, it is safe to exclude a DM component in the dynamical modeling, i.e., the change in BH mass is negligible. When the spatial resolution is marginal, restricting the mass-to-light ratio to the right value returns the correct M_⊙BH although a dark halo is not present in the model. Compared to the M_⊙BH-σ and M M _⊙BH-L relations of McConnell et al., the 10 BHs are all more massive than expected from the luminosities and 7 BH masses are higher than expected from the stellar velocity dispersions of the host bulges. Using new fitted relations, which include the 10 galaxies, we find that the space density of the most massive BHs (M_⊙BH ≳ 10⁹ M _⊙) estimated from the M_⊙BH-L relation is higher than the estimate based on the M_⊙BH-σ relation and the latter is higher than model predictions based on quasar counts, each by about an order of magnitude.