Dynamical modelling of luminous and dark matter in 17 Coma early-type galaxies
Monthly Notices of the Royal Astronomical Society 382:2 (2007) 657-684
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.Constraining black hole masses from stellar kinematics by summing over all possible distribution functions
Monthly Notices of the Royal Astronomical Society 373 (2006) 425-434
The central kinematics of NGC 1399 measured with 14 pc resolution
Monthly Notices of the Royal Astronomical Society 367 (2006) 2-18
Regularized orbit models unveiling the stellar structure and dark matter halo of the Coma elliptical NGC 4807
Monthly Notices of the Royal Astronomical Society 360:4 (2005) 1355-1372
Abstract:
This is the second in a series of papers dedicated to unveiling the mass structure and orbital content of a sample of flattened early-type galaxies in the Coma cluster. The ability of our orbit libraries to reconstruct internal stellar motions and the mass composition of a typical elliptical in the sample is investigated by means of Monte Carlo simulations of isotropic rotator models. The simulations allow a determination of the optimal amount of regularization needed in the orbit superpositions. It is shown that under realistic observational conditions and with the appropriate regularization, internal velocity moments can be reconstructed to an accuracy of ≈15 per cent; the same accuracy can be achieved for the circular velocity and dark matter fraction. In contrast, the flattening of the halo remains unconstrained. Regularized orbit superpositions are applied to a first galaxy in our sample, NGC 4807, for which stellar kinematical observations extend to 3 r eff. The galaxy seems dark-matter dominated outside r > 2 r eff. Logarithmic dark matter potentials are consistent with the data, as well as NFW profiles, mimicking logarithmic potentials over the observationally sampled radial range. In both cases, the derived stellar mass-to-light ratio Υ agrees well with independently obtained mass-to-light ratios from stellar population analysis. The achieved accuracy is ΔΥ ≈ 0.5. Kinematically, NGC 4807 is characterized by mild radial anisotropy outside r > 0.5 r eff, becoming isotropic towards the centre. Our orbit models hint at either a distinct stellar component or weak triaxiality in the outer parts of the galaxy. © 2005 RAS.The centers of early-type galaxies with Hubble Space Telescope. V. New WFPC2 photometry
Astronomical Journal 129:5 (2005) 2138-2185