The SAURON project--IV. The mass-to-light ratio, the virial mass estimator and the Fundamental Plane of elliptical and lenticular galaxies

Abstract

We investigate with unprecedented accuracy the correlations between the\ndynamical mass-to-light ratio M/L and other global observables of E and S0\ngalaxies. We construct two-integral Jeans and three-integral Schwarzschild\ndynamical models for a sample of 25 E/S0 galaxies with SAURON integral-field\nstellar kinematics. We find a tight correlation of the form\n(M/L)=(3.80+/-0.14)*(sigma/200 km/s)^(0.84+/-0.07) between the dynamical M/L\n(in the I-band) and the luminosity-weighted second moment (sigma) of the\nline-of-sight velocity-distribution within Re. The observed rms scatter in M/L\nfor our sample is 18%, while the inferred intrinsic scatter is ~13%. The\n(M/L)-sigma relation can be included in the remarkable series of tight\ncorrelations between sigma and other galaxy global observables. The comparison\nof the observed correlations with the predictions of the Fundamental Plane\n(FP), and with simple virial estimates, shows that the `tilt' of the FP of\nearly-type galaxies, is due to a real M/L variation, while structural and\norbital non-homology have a negligible effect. The virial mass is a reliable\nestimator of the mass in the central regions of galaxies. The best-fitting\nvirial relation has the form (M/L)_vir=(5.0+/-0.1)*Re*sigma^2/(L*G). The\ncomparison of the dynamical M/L with the (M/L)_pop inferred from the analysis\nof the stellar population, indicates a median dark matter fraction in\nearly-type galaxies of ~30% of the total mass inside one Re. (Abridged)\n