John Magorrian

Abstract:

Black hole (BH) masses predicted from the Ṁ-σ relationship conflict with predictions from the Ṁ-L relationship for high-luminosity galaxies, such as brightest cluster galaxies (BCGs). The Ṁ-L relationship predicts that some BCGs may harbor BHs with M approaching 1010 M⊙, while the Ṁ- σ relationship always predicts Ṁ < 3 × 10 9 M⊙. We argue that the Ṁ-L relationship is a plausible description for galaxies of high luminosity. If the cores in central stellar density are formed by binary BHs, the inner core cusp radius, rγ, may be an independent witness of Ṁ. Using central structural parameters derived from a large sample of early-type galaxies observed by HST, we argue that L is superior to σ as an indicator of rγ. Further, the rγ-Ṁ relationship for 11 core galaxies with measured Ṁ appears to be consistent with the Ṁ-L relationship for BCGs. BCGs have large cores appropriate for their large luminosities that may be difficult to generate with the more modest BH masses inferred from the Ṁ-σ relationship. Ṁ ∼ M would be expected for BCGs, if they were formed in dissipationless mergers, which should preserve the ratio of BH to stellar mass, M. This scenario appears to be consistent with the slow increase in a with L and the more rapid increase in effective radii with L seen in BCGs as compared to less luminous galaxies. If BCGs have large BHs commensurate with their luminosities, then the local BH mass function for Ṁ > 3 × 109 M⊙ ould be nearly an order of magnitude richer than that inferred from the Ṁ-σ relationship. The volume density of the most luminous QSOs may favor the Ṁ-L relationship. © 2007. The American Astronomical Society. All rights reserved.

Abstract:

Dynamical models for 17 early-type galaxies in the Coma cluster are presented. The galaxy sample consists of flattened, rotating as well as non-rotating early-types including cD and S0 galaxies with luminosities between MB = -18.79 and -22.56. Kinematical long-slit observations cover at least the major-axis and minor-axis and extend to 1-4reff. Axisymmetric Schwarzschild models are used to derive stellar mass-to-light ratios and dark halo parameters. In every galaxy, the best fit with dark matter matches the data better than the best fit without. The statistical significance is over 95 per cent for eight galaxies, around 90 per cent for five galaxies and for four galaxies it is not significant. For the highly significant cases, systematic deviations between models without dark matter and the observed kinematics are clearly seen; for the remaining galaxies, differences are more statistical in nature. Best-fitting models contain 10-50 per cent dark matter inside the half-light radius. The central dark matter density is at least one order of magnitude lower than the luminous mass density, independent of the assumed dark matter density profile. The central phase-space density of dark matter is often orders of magnitude lower than that in the luminous component, especially when the halo core radius is large. The orbital system of the stars along the major-axis is slightly dominated by radial motions. Some galaxies show tangential anisotropy along the minor-axis, which is correlated with the minor-axis Gauss-Hermite coefficient H4. Changing the balance between data-fit and regularization constraints does not change the reconstructed mass structure significantly: model anisotropies tend to strengthen if the weight on regularization is reduced, but the general property of a galaxy to be radially or tangentially anisotropic does not change. This paper is aimed to set the basis for a subsequent detailed analysis of luminous and dark matter scaling relations, orbital dynamics and stellar populations. © 2007 The Authors.