Isotropic dynamical models of NGC 4472 (M 49)

Context. The existence of dark matter in some early-type galaxies is well-established. We address one such case and study dynamical models of NGC 4472 by means of using both Newtonian and MOdified Newtonian Dynamics (MOND) approaches with particular emphasis on the latter. Aims. We use the measurements of the radial velocities of globular clusters in NGC 4472 to test the predictions of dynamical models to fit a high and approximately constant value the velocity dispersion with radius for this galaxy. Methods. The globular clusters of NGC 4472 are used as a tracer of the galaxy's gravitational potential. We calculate the Jeans equation for both the Newtonian (mass-follows-light and dark-matter models) and the MOND approaches assuming spherical symmetry and isotropic orbits. Results. We solve the isotropic Jeans equation for a spherical approximation and find, assuming a rotational velocity of 50 km s(-1), that the isotropic Newtonian mass-follows-light models without dark matter cannot provide successful fits at radii larger than similar to 2 R-e and that in the Newtonian approach dark matter is needed. Of the four different MOND models that we tested, two models can provide a successful fit to the velocity dispersion throughout the whole galaxy without assuming any anisotropy (again assuming a rotational velocity of 50 km s(-1)), thus showing that in the case of NGC 4472 MOND can describe the dynamics of a massive early-type galaxy with high values of velocity dispersion.