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Given the recently deduced relationship between X-ray temperatures and stellar velocity dispersions (the T-sigma relation) in an optically complete sample of elliptical galaxies (Davis & White 1996), we demonstrate that L>L_* ellipticals contain substantial amounts of dark matter in general. We present constraints on the dark matter scale length and on the dark-to-luminous mass ratio within the optical half-light radius and within the entire galaxy. For example, we find that minimum values of dark matter core radii scale as r_dm > 4(L_V/3L_*)^{3/4}h^{-1}_80 kpc and that the minimum dark matter mass fraction is >~20% within one optical effective radius r_e and is >~39-85% within 6r_e, depending on the stellar density profile and observed value of beta_spec. We also confirm the prediction of Davis & White (1996) that the dark matter is characterized by velocity dispersions that are greater than those of the luminous stars: sigma_dm^2 ~ 1.4-2 sigma_*^2. The T-sigma relation implies a nearly constant mass-to-light ratio within six half-light radii: M/L_V ~ 25h_80 M_sun/L_V_sun. This conflicts with the simplest extension of CDM theories of large scale structure formation to galactic scales; we consider a couple of modifications which can better account for the observed T-sigma relation.
We review X-ray constraints on dark matter in giant elliptical galaxies (10^{12} M_sun <~ M_vir <~ 10^{13} M_sun) obtained using the current generation of X-ray satellites, beginning with an overview of the physics of the hot interstellar medium and
There is strong evidence that the mass in the Universe is dominated by dark matter, which exerts gravitational attraction but whose exact nature is unknown. In particular, all galaxies are believed to be embedded in massive haloes of dark matter. Thi
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