The Fundamental Plane of Ellipticals: I. The Dark Matter Connection
Abstract
In spiral galaxies the stellar disk dominates the inner mass distribution. By using the Fundamental Plane (FP) as a powerful tool to derive the properties of the dark and the luminous matter, we find that the above claim holds also for Ellipticals. This result enlightens the issue of dark and luminous matter in spheroids. We show that the `central velocity dispersion' appearing in (e.g.) the Fundamental Plane, is linked, in a complex, but predictable way, to photometric, dynamical and geometrical quantities of both luminous and dark matter. Then, the very existence of the Fundamental Plane strongly constraints the mass models. In particular,it implies i) an average value for the dark-to-luminous mass ratio (inside the galaxy effective radius) of about 0.3 ii) a stellar mass-to-light increasing with spheroid luminosity as L^(0.2) in Gunn-r band, with a value of ~ 5.3 at L_(star) and iii) cored dark matter halos around ellipticals, as found for both dwarf and spiral galaxies. On the other hand, we find that Lambda CDM is unable to explain the very existence of the FP: this theory has structural properties of dark and luminous matter so interwoven that, in the space (sigma_0, r_e, L), it predicts a curved surface, rather than a plane.Keywords
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