Dynamical Models and Anisotropy of the Velocity Dispersions in Elliptical Galaxies

Аннотация

Models for 12 elliptical galaxies are constructed based on the second-order tensor virial theorem. This method takes into account the spatial shape and structure of the internal density layers for each galaxy. New data for the surface brightness and isophote structure of the E galaxies derived from deep photometric observations are used. A system of equations is used to find the components of the gravitational-energy, rotational-energy, and velocity-dispersion tensors. This makes it possible to calculate the anisotropy index β of the velocity dispersion of each galaxy. The values for the entire sample lie in the range 0.012 ⩽ β ⩽ 0.246. It is shown that taking into account variations in the mass-to-light ratio M/L (for the stellar component) can reduce the value of β by roughly 20%. The results are compared with those from other studies. Our values of β for small E galaxies (rapid rotators) agree with those found in the ATLAS^3D project based on Jeans anisotropy models. However, our models for giant E galaxies (slow rotators) taking into account the triaxial shape and realistic structure of the density layers provide a much better agreement with observations than the simple axially symmetrical models from the SAURON project.