Dynamical evidence for a central mass concentration in the galaxy M87

Abstract

An image photon-counting system operating in a fully two-dimensional mode has been used to determine the radial variation of radial velocity, line strength, and velocity dispersion in the elliptical galaxies M87 and NGC 3379. Values of these parameters are derived by an application of the Fourier method due to Sargent et al. (1977). Extensive tests of the Fourier method are performed, the measurements are compared with models, and a model-independent analysis is described along with a model-independent procedure for obtaining the M/L ratio as a function of radius. The results show that the two galaxies behave quite similarly in their outer regions but exhibit quite different properties in their central regions and that a dark central mass estimated to be 5 billion solar masses must be concentrated in M87 in a volume with a radius (in parsecs) of 110 times a distance factor. It is concluded that the presence of a central supermassive black hole on M87 must be a serious possibility.