Orbital structure and mass distribution in elliptical galaxies

We report on a homogeneous dynamical analysis of a sample of 21 round (17 E0/E1, 4 E2) elliptical galaxies. We present new kinematic data for eight of these galaxies and new photometry for one object. The remaining kinematic and photometric data and the required distance information are taken from the literature. The analysis uses non-parametric spherical models and takes into account line profile information as well as velocity dispersions. We present model fits to the kinematic data and the derived radial profiles of orbital anisotropy and B-band mass-to-light ratio, including confidence intervals. The circular velocity curves resulting from our model fits are all consistent with being flat outside $R\approx 0.3 R_{\rm e}$. Generally, the $M/L$ ratio profiles show an outward increase, although models based on luminous matter are ruled out at 95% confidence only for three galaxies (NGC 2434, NGC 7507, NGC 7626). For NGC 1399, NGC 4472, NGC 4486, and NGC 4636, where X-ray observations are available, the mass profiles of the best fit models match the ones derived from the X-ray analysis. The best models for most galaxies are isotropic to slightly radially anisotropic, with typical $\beta\,\raisebox{0.4ex}{$<$}\raisebox{-0.4ex}{$\!\!\!\!\!\!\;\sim$}\,0.3$, in a few cases $\beta\,\raisebox{0.4ex}{$<$}\raisebox{-0.4ex}{$\!\!\!\!\!\!\;\sim$}\,0.5$ at $R_{\rm e}/2$. We discuss the generally small effects of flattening along the line-of-sight (the expected $\!$ = 0.79 for this sample of luminous ellipticals) and of small embedded disks. Our results suggest that elliptical galaxies have surprisingly uniform dynamical properties.