ELLIPTIC GALAXIES WITH DARK MATTER .2. OPTIMAL LUMINOUS DARK MATTER DECOMPOSITION FOR A SAMPLE OF BRIGHT OBJECTS

A procedure for the analysis of photometric and kinematical profiles of elliptical galaxies based on a family of spherical, pressure supported, self-consistent two-component models described in a previous paper is developed as a tool to study the presence of dark halos in such systems. Several tests on simulated objects are performed in order to show that this procedure is able to recognize the presence of dark matter, when sufficiently accurate and extended profiles are available; some of these tests have been carried out on flattened objects (E4 and E6), in order to establish how geometry can affect our conclusions. Then we have fitted the most accurate and extended data available for a set of 10 bright nearly round ellipticals. Very good photometric and kinematical fits are obtained; in some of these cases, the preferred models have a massive and diffuse dark component. In general, the amount of dark matter found inside R(e) is not too large, of the order of the luminous mass. Typically, the mass-to-light ratio that we derive inside R(e) is M(L)/L(B) approximately 7 M./L. for the stellar component, and (M/L(B))(R(e)) approximately 12 M./L. for the sum of the two components. For NGC 4472 the velocity dispersion profile of the best-fit model is found to be well in agreement with the observed kinematics of the globular cluster system; in addition, an analysis devised to assess the statistical significance of the results obtained indicates that the amount of dark matter present in this galaxy exceeds that of the luminous component at a 3 sigma confidence level.