2000ApJ...536..319C

We present direct observational constraints on the orbital distribution of the stars in the giant elliptical NGC 2320. Long-slit spectra along multiple position angles are used to derive the stellar line-of-sight velocity distribution within one effective radius, R_eff. In addition, the rotation curve and dispersion profile of an ionized gas disk are measured from the [O III] emission lines. After correcting for the asymmetric drift, we derive the circular velocity of the gas, which provides an independent constraint on the gravitational potential. To interpret the stellar motions, we build axisymmetric three-integral dynamical models based on an extension of the Schwarzschild orbit-superposition technique. We consider two families of gravitational potential, one in which the mass follows the light (i.e., no dark matter) and one with a logarithmic gravitational potential. Using χ² statistics, we compare our models to both the stellar and gas data to constrain the value of the V-band mass-to-light ratio, Υ_V. We find Υ_V=15.0±0.6 h₇₅ for the mass-follows-light models and Υ_V=17.0±0.7 h₇₅ for the logarithmic models. For the latter, Υ_V is defined within a sphere of 15'' radii. Models with radially constant Υ_V and logarithmic models with dark matter provide comparably good fits to the data and possess similar dynamical structure. Across the full range of Υ_V permitted by the observational constraints, the models are radially anisotropic in the equatorial plane over the radial range of our kinematical data (1''≲r≲40''). Along the true minor axis, they are more nearly isotropic. The best fitting model has σ_r/σ_total≃0.7, σ_φ/σ_total≃0.5-0.6, and σ_θ/σ_total≃0.5 in the equatorial plane.